Bibliography

Bibliography in endnote format

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Marble, D. F. (1980). Computer software for spatial data handling. [Reston, Va., U.S. Geological Survey, 1980?] 3 v. (viii, 1042 p.) : ill.

Redondo, F. (1981). The Use of remotely sensed data and geographic information systems as tools for crop production forecasting : a training report. Brookings, S.D., U.S.A., Remote Sensing Institute, South Dakota State University, [1981] viii, 64 leaves : ill.

Hedman, V. (1985). "GPS satellite control for photogrammetric cadastral surveys." Eng Field Notes U S For Serv Eng Staff 17: 39-54.

Antenucci, J. (1986). "Geographic information systems and implementation considerations."

Berry, J. K. (1986). "Geographic information systems. III. Learning computer-assisted map analysis." J For 84(10): 39-43.

Devine, H. A. and R. C. Field (1986). "The gist of GIS." J For 84(8): 17-22.

Brown, D. A. and P. Gersmehl (1987). File structure design and data specifications for water resources geographic information systems. St. Paul, MN, Water Resources Research Center, University of Minnesota, [1987] 1 v. (various pagings) : ill. (some col.), maps.

Dillaha, T. A., R. K. Byler, et al. (1987). "Estimating sediment delivery ratios using geographic information systems." Am Soc Agric Eng Microfiche Collect(fiche no. 87-2106): 17.

MacDougall, E. B., M. Gross, et al. (1987). The feasibility of geographic information systems : a model study. Amherst, Mass., Massachusetts Agricultural Experiment Station, College of Food and Natural Resources, Univ. of Massachusetts, 1987. iv, 51 p.

Mouland, D. J. (1987). "Valle Vidal Global Positioning System (GPS) demonstration project." Eng Field Notes U S For Serv Eng Staff 19: 9-12.

Robinson, V. B., A. U. Frank, et al. (1987). "Expert systems for geographic information systems in resource management." AI Appl Nat Resour Manage 1(1): 47-56.

(1988). National GIS plan : geographic information system. Washington, D.C., U.S. Dept. of State, Forest Service, Information Systems, [1988] 14 p.

Barker, G. R. (1988). "Remote sensing: the unheralded component of geographic information systems." Photogramm Eng Remote Sensing 54(2): 195-199.

Becker, F. and B. J. Choudhury (1988). "Relative sensitivity of normalized difference vegetation index (NDVI) and microwave polarization difference index (MPDI) for vegetation and desertification monitoring." Remote Sens Environ 24: 297-311.

Borgelt, S. C. (1988). "Geographic information systems for on-farm use." Am Soc Agric Eng Microfiche Collect(fiche no. 88-1606): 36.

Corwin, D. L. and J. D. Rhoades (1988). "The use of computer-assisted mapping techniques to delineate potential areas of salinity development in soils. II. Field verification of the threshold model approach." Hilgardia J Agric Sci 56(2): 18-32.

Friedl, M. A., J. E. Estes, et al. (1988). "Advanced information-extraction tools in remote sensing for earth science applications: AI and GIS." AI Appl Nat Resour Manage 2(2/3): 17-31.

Gage, S. H., G. A. Simmons, et al. (1988). "Computer based geographic information systems for regional decisions in pest management." Ext Bull E Coop Ext Serv Mich State Univ(2142): 52-58.

Hedman, V. (1988). "Four years of using GPS." Eng Field Notes U S Dep Agric For Serv Eng Staff 20: 33-48.

Johnston, C. A., N. E. Detenbeck, et al. (1988). "Geographic information systems for cumulative impact assessment." Photogramm Eng Remote Sensing 54(11): 1609-1615.

Larsen, W. E., D. A. Tyler, et al. (1988). "Field navigation using the global positioning system (GPS)." Am Soc Agric Eng Microfiche Collect(fiche no. 88-1604): 10.

McLemore, W. H. and S. J. Alhadeff (1988). Using geographic information systems for environmental decision making. [Atlanta], Dept. of Natural Resources, Environmental Protection Division, Georgia Geologic Survey, 1988. vi, 95 leaves : ill. (some col.).

Miller Weeks, M., J. Spruce, et al. (1988). "Utilizing color infrared aerial photography and GIS technology to map red spruce and balsam fir mortality in New York, Vermont, New Hampshire, and western Maine."

(1989). The potential for geographic information systems in agricultural economics : proceedings of a symposium at the annual meeting of the American Agricultural Economics Association, July 30-August 2, Louisiana State University, Baton Rouge, Louisiana. [S.l., American Agricultural Economics Association, 1989] 40 leaves : ill.

Biggs, P. H., C. J. Pearce, et al. (1989). "GPS navigation for large-scale photography." Photogramm Eng Remote Sensing 55(12): 1737-1741.

Brown, D. A. and P. J. Gersmehl (1989). "Geographic information systems, data, and water resources." J Minn Acad Sci 55(1): 14-17.

Chuvieco, E. and R. G. Congalton (1989). "Application of remote sensing and geographic information systems to forest fire hazard mapping." Remote Sensing Environ 29(2): 147-159.

Coulson, R. N., L. A. Graham, et al. (1989). "Intelligent geographic information systems and landscape management." AI Appl Nat Resour Manage 3(3): 70.

Diehl, K. (1989). "Streamlining the NRI." Soil Water Conserv U S Dep Agric Soil Conserv Serv 10(6): 7-8.

Liang, T. and Q. L. Meng (1989). "Ecological variables in harvesting system optimization." Pap Amer Soc Agric Eng(89-7022): 16.

Luloff, A. E. and W. A. Befort (1989). "Land use change and aerial photography: lessons for applied sociology." Rural Sociol 54(1): 92-105.

Mausbach, M. J., D. L. Anderson, et al. (1989). "Soil survey databases and their uses."
The Soil Conservation Service (SCS) through the National Cooperative Soil Survey (NCSS) maintains databases at three levels; national, state, and field (local). They contain information on properties of the soil series of the United States and for the map units of individual project soil surveys. An overall soil information system is currently being designed with the goal to develop, support, and maintain a coordinated (integrated), distributive system. The national databases include the Official Soil Series Description (OSED), Soil Interpretations Record (SIR, SOI-5), Map Unit Use File (MUUF), Soil Classification File (SC), and National Soil Survey Area Database (NSSAD). They contain the definitions or descriptions for soil series and map units of the NCSS. These databases are used in quality assurance and quality control; in developing predictive models; to provide attribute data for geographic information systems; and for national queries of soil properties. Analytical data will be stored in the National Soil Characterization Database (NSCDB). It will contain site specific morphological and analytical data used in developing series definitions and soil parameter relationships. Other national databases include soil performance data and the National Soil Geographic data (NATSGO). State databases include State Soil Survey Database (SSSD) and State Geographic data (STATSGO). The SSSD contains information on map unit properties and interpretations for individual surveys and STATSGO is the digitized general soil map for the state. Local or field soil databases are the Map Unit Interpretations Record (MUIR) and the geographic soil map data (SSURGO) for a soil survey area. These databases together form the core of the local Geographic Information System.

Turbak, G. (1989). "A new way to find your way." Am For 95(7/8): 10-11, 48.

Wilkie, D. S. (1989). "Performance of a backpack GPS in a tropical rain forest." Photogramm Eng Remote Sensing 55(12): 1747-1749.

Winn, D. S., R. E. Beverly, et al. (1989). Proceedings : Geographic Information Systems Awareness Seminar. [Ogden, Utah?], U.S. Dept. of Agriculture, Forest Service, Intermountain Region, [1989?]] 84 p. : ill.

(1990). GIS application note. Atlanta, GA, United States Dept. of Agriculture, Forest Service, Southern Region, [1990?- v. : maps.

(1990). Understanding GIS : the ARC/INFO method. Redlands, CA, Environmental Systems Research Institute, c1990. 1 v. (various pagings) : ill., maps.

(1990). A Study of land information. [Washington, D.C.?, The Dept., 1990] 1 v. (various pagings) : ill.

Barker, G. R. (1990). "Information resource management--the promise and the challenge."

Engel, B. A. and L. D. Gaultney (1990). "Environmentally sound agricultural production systems through site-specific farming." Pap Amer Soc Agric Eng(90-2566): 7.

Gerlach, F. L. (1990). "Global position system--input to GIS."

Gerlach, F. L. and A. E. Jasumback (1990). "Status and projections for implementation of GPS."

Gerlach, F. L. (1990). "Returning space to earth using the global positioning system."

Herrington, L. P. (1990). "Geographic information systems: where do we stand." U S D A For Serv Gen Tech Rep PNW GTR Pac Northwest Res Stn(263): 391-396.

Larson, K. M. (1990). Precision, accuracy, and tectonics from the Global Positioning System. 1990. xv, 269 leaves, ill., maps.

Li, Z. L. and F. Becker (1990). "Properties and comparison of temperature-independent thermal infrared spectral indices with NDVI for HAPEX data." Remote Sensing Environ 33(3): 165-182.

Mason, J. P. (1990). Application of geographic information systems, simulation models, and knowledge-based systems for landuse management : proceedings, November 12-14, 1990, Donaldson Brown Center for Continuing Education. Blacksburg, Va., The Dept. 28 cm. ix, 555 p. : ill., maps.

Myhre, B. E. and S. F. Shih (1990). "Use of geographic information systems for a well monitoring program." Proc Soil Crop Sci Soc Fla 49: 18-20.

Nellis, M. D., K. Lulla, et al. (1990). "Interfacing geographic information systems and remote sensing for rural land-use analysis." Photogramm Eng Remote Sensing 56(3): 329-331.

Osborne, S. (1990). "Growth models and geographic information systems." U S D A For Serv Gen Tech Rep PNW GTR Pac Northwest Res Stn(263): 397-402.

Sage, R. J. (1990). "Geographic Information Systems: the marriage of mapping and computer graphics." Eng Ext Ser Purdue Univ(161): 38-42.

Sucksdorff, Y. and C. Ottle (1990). "Application of satellite remote sensing to estimate areal evapotranspiration over a watershed." J Hydrol 121(1/4): 321-333.
A method for estimating areal evapotranspiration by using synoptical weather data and satellite imagery is presented. Recent studies have shown that if atmospheric and surface parameters are known, the energy and hydraulic budgets at the soil/vegetation/atmosphere interface can be simulated. Then, soil temperature estimated by thermal infrared remote sensing can be used to derive the energy fluxes as far as they are the equilibrium term of the energy budget. This methodology has been applied in southwestern Finland over the Eurajoki River basin. The model was first calibrated with ground measurements and satellite data. The NDVI and the surface temperature estimated from NOAA/AVHRR data have been used to calibrate the leaf area index and the minimum resistance to evapotranspiration. The different land use classes over the river basin were interpreted from LANDSAT/TM images, and the model was then run over the whole month of July 1988 for all the most important soil and vegetation types of the river basin. Finally, the total derived evaporation was compared with the one estimated by a water balance method applied over the month of July.

(1991). U.S. Department of Agriculture Geographic Information Systems Work Group : report to the Secretary. [Washington, D.C.?, U.S. Dept. of Agriculture, 1991] [24] p. : ill.

(1991). Remote sensing and GIS applications to nonpoint source planning : workshop proceedings, Quality Inn Downtown, Chicago, Illinois, October 1-3, 1990. Washington, D.C., Terrene Institute, [1991] iv, 124 p. : ill., maps.

(1991). National geographic information structure. Washington, D.C., U.S. Dept. of Agriculture, Forest Service, Computer Sciences & Telecommunications, [1991] 11 p.

(1991). The Local government guide to geographic information systems : planning and implementation. Washington, D.C., PTI (Public Technology, Inc.) : International City Management Association, c 1991. 126 p. : ill., maps.

(1991). A Geographic information systems guidebook : for use in the Integrated Resource Management process. [Albuquerque, N.M.?], U.S. Dept. of Agriculture, Forest Service, Southwestern Region, 1991. 73 p. : col. ill., maps (some col.).

Arthaud, G. J. (1991). "Implementing and integrating multi-resource models in geographic information systems."

Auernhammer, H. and T. Muhr (1991). "GPS in a basic rule for environmental protection in agriculture."

Dangermond, J. (1991). "Where is the technology leading us." For Chron 67(6): 599-603.
With GIS technology now about 25 years old, it is appropriate to consider where GIS use may he leading us, with special reference to natural resource management uses and considering forest management in particular. After beginning with a consideration of where GIS technology is going, and with mention of several important related technologies, the paper considers the range of problems and of possible immediate futures for natural resource management generally, and for forest management in particular. The role of GIS in natural resource management is taken up next. Some comments on who determines where GIS technology will go in the future are offered. The paper concludes with a consideration of where GIS technology may lead natural resource management in the next decade and just after the turn of the century.

Dowman, I. (1991). Spatial data 2000 : proceedings of a joint conference of the Photogrammetric Society, the Remote Sensing Society, the American Society for Photogrammetry and Remote Sensing : Christ Church, Oxford, 17th-20th September 1991. London, Dept. of Photogrammetry and Surveying, University College London, [1991] ix, 325 p. : ill.

Falbo, D. L., L. P. Queen, et al. (1991). Introduction to data analysis using geographic information systems. Saint Paul, MN, Minnesota Extension Service, University of Minnesota, 1991. 11 p. : ill.

Fletcher, J. J. and T. T. Phipps (1991). "Data needs to assess environmental quality issues related to agriculture and rural areas." Am J Agric Econ 73(3): 926-932.

Hammer, R. D., J. H. Astroth, Jr., et al. (1991). "Geographic information systems for soil survey and land-use planning." SSSA Spec Publ Ser(28): 243-270.

Hunsaker, C. T. (1991). Spatial models of ecological systems and processes : the role of GIS : International Conference/Workshop on Integrating Geographic Information Systems and Environmental Modeling, 15-18 September 1991, Boulder, Colorado. [S.l., s.n. 1991?] 36 p.

Karlen, D. L. and T. E. Fenton (1991). "Soil map units: basis for agrochemical-residue sampling." A C S Symp Ser Am Chem Soc(465): 182-194.
Representative sample collection is the most critical step in any program designed to determine how soil and crop management affects the presence of agrochemical residues such as nitrate nitrogen or pesticides. Soil map units within the soil classification system, can be used to develop sampling plans with comparable soil bodies despite natural soil diversity. Soil map unit data can be analyzed statistically and used to provide information for geographic information systems (GIS). Use of soil map units for selecting sampling sites to evaluate current and alternate management practices on agrochemical residues is recommended.

Klock, G. O. (1991). "Potential use of geographic information systems to enhance forest soil management." Gen Tech Rep INT U S Dep Agric For Serv Intermt Res Stn(280): 180-182.

Lai, P. (1991). "Issues concerning the technology transfer of geographic information systems." Environ Manage 15(5): 595-601.

Lam, D. C. L. (1991). "Integrating database, spreadsheet, graphics, GIS, statistics, simulation models and expert systems: experiences with the RAISON system on microcomputers." NATO ASI Ser Ser G Ecol Sci 26: 429-459.

Larsen, W. E., D. A. Tyler, et al. (1991). "Using the GPS satellites for precision navigation."

Lees, B. G. and K. Ritman (1991). "Decision-tree and rule-induction approach to integration of remotely sensed and GIS data in mapping vegetation in disturbed or hilly environments." Environ Manage 15(6): 823-831.

Long, D. S., S. D. DeGloria, et al. (1991). "Use of the global positioning system in soil survey." J soil water conserv 46(4): 293-297.

Mahey, R. K., R. Singh, et al. (1991). "The use of remote sensing to assess the effects of water stress on wheat." Exp Agric 27(4): 423-430.

Masser, I. and M. Blakemore (1991). Handling geographical information : methodology and potential applications. Harlow, Essex, England, Longman Scientific & Technical ; New York : Wiley, 1991. xii, 317 p., [8] p. of plates : ill. (some col.), maps.

Myhre, B. E. and S. F. Shih (1991). "Using geographic information systems in a well permitting program." Proc Soil Crop Sci Soc Fla 50: 102-105.

Olimpio, J. C. (1991). Use of a geographic information system to assess risk to ground-water quality at public-supply wells, Cape Cod, Massachusetts. Boston, Mass., U.S. Dept. of the Interior, U.S. Geological Survey ; Denver, CO : Books and Open-File Reports Section [distributor], 1991. v, 35, 10 p. : ill., maps (some col.).

Persson, J. and E. Jungert (1991). Generation of multi-resolution maps. Linkoping, Sweden, National Defence Research Establishment, Dept. of Information Technology, [1992] 66 p. : ill., maps.

Petersen, G. W. (1991). Evaluation of agricultural nonpoint pollution potential in Pennsylvania using a geographic information system. University Park, PA, Penn State Environmental Resources Research Institute, [1991?] iv, 60 p. : ill., maps.

Shaw, R. R. (1991). "Managing the land: a technology perspective." J Soil Water Conserv 46(6): 406-408.

Shultz, S. and J. Regan (1991). "The 1990 census, GIS technology, and rural data needs." Rural Sociol 11(1): 23-29.

Smith, J. L. (1991). "Dynamic digital databases: the key to practical land classification systems." Gen Tech Rep SE U S Dep Agric For Serv Southeast For Exp Stn(68): 105-109.

Srinivasan, R. and B. A. Engel (1991). "Effect of slope prediction methods on slope and erosion estimates." Appl Eng Agric 7(6): 779-783.
Geographic Information Systems (GIS) can be used to reduce data collection demands by extracting valuable information from existing data bases. One important application is in estimating slope steepness, which is a critical factor in estimating soil loss and chemical movement. Four algorithms/techniques that have been widely used to predict slope from elevation data sets, such as those found in raster-based GIS, are described. Using two 10x10 cell data sets, the slope and USLE LS-factor were estimated for each grid cell using each method and then compared. Estimates of slopes for these areas were also obtained from topographic maps and site observation. Significant differences in the estimated slopes between methods were found. The effects of slope estimation techniques on non-point source models are demonstrated and discussed.

Starr, J. L. (1991). The integration of remote sensing and geographic information systems : Proceedings of a special session held at the Baltimore 1991 ACSM-ASPRS Annual Convention. Bethesda, Md., American Society for Photogrammetry and Remote Sensing. c1991 vi, 195 p. : ill.

TeSelle, G. W. (1991). "Geographic information systems for managing resources."

Wallis, J. R. (1991). "The interface between GIS and hydrology." NATO ASI Ser Ser G Ecol Sci 26: 189-197.

Wiggins, L. L. and S. P. French (1991). GIS : assessing your needs and choosing a system. Chicago, IL (1313 E. 60th St., Chicago 60637), American Planning Association, c1991. 26 p. : ill., maps.

Assad, E. D. (1992). Description of native areas by means of remote sensing and geographic information systems. Planaltina, DF, Empresa Brasileira de Pesquisa Agropecuaria, Centro de Pesquisa Agropecuaria dos Cerrados, 1992. 23 p. : maps (1 col.).

Barrett, G. W. (1992). "Landscape ecology: designing sustainable agricultural landscapes." J Sustainable Agric 2(3): 83-103.

Becker, H. and D. Senft (1992). "Satellites key to new farming aids." Agric Res U S Dep Agric Res Serv 40(2): 4-8.

Bolstad, P. V. and J. L. Smith (1992). "Errors in GIS." J For 90(11): 21-29.

Bolstad, P. V. (1992). "Geometric errors in natural resources GIS data: tilt and terrain effects in aerial photographs." For Sci 38(2): 367-380.
Simulation studies were performed to estimate geometric errors in spatial data from monoscopic interpretation of large format aerial photographs. Positional and area error were simulated for a range of photo scales (1:10,000 to 1:40,000), camera tilts (0 degrees to 4.2 degrees), and relief (vertical range from 0 m to 750 m). Average positional errors were observed between 4 m and 104 m and varied positively with tilt and terrain range and inversely with scale. Area errors were observed over a range of polygon sizes, from 40 to 600 ha. Average area error ranged from 0.0 to 10.7% and was positively related to tilt and terrain range and not related to scale or polygon size. The magnitude of these errors and the availability and low cost of requisite correction technologies suggest analytical methods for removing relief and tilt distortion should be employed under most circumstances.

Congalton, R. G. and K. Green (1992). "The ABCs of GIS." J For 90(11): 13-20.

Coulson, R. N. (1992). "Intelligent geographic information systems and integrated pest management." Crop Prot 11(6): 507-516.

Deichert, L. A. and J. M. Hamlett (1992). "Nonpoint ground-water pollution potential in Pennsylvania." Pap Am Soc Agric Eng(922531): 25.

Dwyer, J. L. and J. T. Nash (1992). Spatial analysis of geochemical and geologic information from the Tonopah 10 x 20 quadrangle, Nevada. Washington [D.C], b U.S. G.P.O. ; Denver, CO : For Sale by the Books and Open-File Reports Section, U.S. Geological Survey [distributor], 1992. iv, 21 p. : ill., maps (some col.).

Flowers, C., D. W. Parvin, Jr., et al. (1992). "The economic impact of boll weevils in Mississippi: a GIS perspective." Proc Beltwide Cotton Prod Res Conf 1: 386-388.

Green, K. (1992). "Spatial imagery and GIS." J For 90(11): 32-36.

Harrison, J. D., S. J. Birrell, et al. (1992). "Global positioning system applications for site-specific farming research." Pap Am Soc Agric Eng(923615): 14.

Jasumback, T. and J. Tour (1992). Engineering tech tips. [United States], U.S. Dept. of Agriculture, Forest Service, Technology & Development Program?, 1992- v. : ill.

Jensen, J. R., S. Narumalani, et al. (1992). "Predictive modeling of cattail and waterlily distribution in a South Carolina reservoir using GIS." Photogramm Eng Remote Sensing 58(11): 1561-1568.

Johnson, A. I., C. B. Pettersson, et al. (1992). Geographic Information Systems (GIS) and mapping : practices and standards. Philadelphia, ASTM, c1992. 346 p. : ill.

Kessler, B. L. (1992). "Glossary of GIS terms." J For 90(11): 37-45.

Lachowski, H., P. Maus, et al. (1992). "Integrating remote sensing with GIS." J For 90(12): 16-21.

Lee, J. K., R. A. Park, et al. (1992). "Application of geoprocessing and simulation modeling to estimate impacts of sea level rise on the northeast coast of Florida." Photogramm Eng Remote Sensing 58(11): 1579-1586.

Loh, D. K. and E. J. Rykiel, Jr. (1992). "Integrated resource management systems: coupling expert systems with data-base management and geographic information systems." Environ Manage 16(2): 167-177.

Martz, E. (1992). "Information flows."

Miller, B. M. (1992). Guide to the development and application of geographic information systems for sedimentary basin analysis : case study for the San Juan Basin, New Mexico and Colorado. Washington, D.C., U.S. G.P.O. ; Denver, CO : For sale by Book and Open-File Report Sales, U.S. Geological Survey, 1992. iv, 37 p. : ill. (some col.), maps (some col.).

Parker, W. H. (1992). "Focal point seed zones: site-specific seed zone delineation using geographic information systems." Can J For Res J Can Rech For 22(2): 267-271.
A new site-specific approach to defining seed zones in North American conifers is described. Using focal point seed zones, an individual site to be reforested becomes the focal point, and a unique seed zone is established for that site as needed. This approach depends upon (i) obtaining good comparative data in adaptive characteristics from throughout the range to be regenerated based upon a series of short-term growth tests in a common garden and (or) greenhouse and (ii) graphic analysis of multivariate summary scores by geographic information systems software to delimit boundaries of unique seed zones for any location to be reforested. A sample focal point seed zone is delineated for jack pine (Pinus banksiana Lamb.) reforestation of a site in northern Ontario. This approach has considerable potential to help prevent decreased growth and yield due to the planting of maladapted seed.

Price, K. P., D. A. Pyke, et al. (1992). "Shrub dieback in a semiarid ecosystem: the integration of remote sensing and geographic information systems for detecting vegetation change." Photogramm Eng Remote Sensing 58(4): 455-463.

Reinhardt, R. D. (1992). Geographic information systems (GIS)--a global perspective. Arlington, MA, Cutter Information Corp., c1992. 109 p. : ill.

Schueller, J. K. (1992). "A review and integrating analysis of spatially-variable control of crop production." Fertil res 33(1): 1-34.
The variability of crops, soils, and pests within crop production fields has led to attempts to understand those variations and to manage crop production accordingly. The rapidly expanding research and development on the management and control of crop production according to in-field variations is reviewed. The various stages and components of this spatially-variable control are classified and presented along with a proposed terminology and notation. Advances in component technologies (sensors, actuators, locators, geostatistics, geographic information systems) and their integration should reduce crop production costs and be environmentally advantageous.

Smith, J. L., J. A. Logan, et al. (1992). "Using aerial photography and geographic information systems to develop databases for pesticide evaluations." Photogramm Eng Remote Sensing 58(10): 1447-1452.

Svoboda, M. D. (1992). A spatial and temporal analysis of the relationship between precipitation and NDVI as calculated from AVHRR data. 1992. vii, 85 leaves, ill.

Tauer, W. and G. Humborg (1992). Runoff irrigation in the Sahel zone : remote sensing and geographical information systems for determining potential sites. Ede, Netherlands, CTA ; Weikersheim, FR Germany : Verlag Josef Margraf Scientific Books [distributor], c1992. 192 p. : ill. (some col.).

Thenkabail, P. S., A. D. Ward, et al. (1992). "Landsat Thematic Mapper indices for evaluating management and growth characteristics of soybeans and corn." Trans A S A E 35(5): 1441-1448.
Landsat satellite Thematic Mapper (TM) data from 25 August 19.88 were used to extract information on corn and soybean crops in Seneca County, Ohio. Specific objectives included the evaluation of satellite TM data indices to: (a) quantify field differences in corn and soybean crop parameters at critical and senescing growth stages; (b) determine if the ground truth and satellite TM data could be used to identify and quantify soil type and agricultural management practice influences on crop development; and (c) evaluate the suitability of the ground truth data and identify data collection modifications that would improve the practicality of using satellite data. The TM data were evaluated in terms of brightness values and vegetation indices for each farm at a spatial scale of 10 pixels. Discrete ranges of the normalized difference vegetation index, NDVI, and the stress-related vegetation index, STVI, were used to identify crop management and soil differences. A comparison was made between using the following methods for quantifying ground truth crop parameters and then correlating them to satellite data: (a) measured data on the day of the satellite overpass; (b) estimates of crop characteristics based on fitting polynomial equations to data collected throughout the growing season; and (c) estimates based on a 3-point mean of data from the day of the overpass and the sampling episodes prior to and following the overpass. NDVI and STVI data correlated best to the polynomial equation estimates of crop variables. The correlation of individual indices with crop variables was generally poor but combinations of bands and indices can be used to describe between 50 and 70% of the between field variability in leaf area index, plant biomass, and crop yield. Generally, TM vegetation indices can be used to identify significant differences in crop responses to different management systems. These differences were mainly a function of plant density, management problems associated with drought conditions, and tillage.

Tim, U. S., M. Milner, et al. (1992). "Geographic Information Systems Simulation Model Linkage: Processes, problems and opportunities." Pap Am Soc Agric Eng(92-3610): 20.

Van Sickle, G. A. (1992). "A review of innovations in disease and insect management and control." For Chron 68(6): 742-746.
Insects, diseases and fire annually cause losses equal to one-third of the allowable annual cut in British Columbia and can directly affect exports and movement of forest products. While salvage, at least partial, of the merchantable mortality has been the traditional practice, innovations in forecasting, detection and control are increasing forest management options. Examples are given of technological advances in nursery production, data analysis and interpretation using geographic information systems (GIS) and models, insect pheromones and biological controls, and quarantine requirements imposed by concerns for potential pests.

Wallace, A. (1992). "Professional schools for agriculture." HortScience 27(1): 10.

Wessman, C. A. (1992). "Spatial scales and global change: bridging the gap for plots to GCM grid cells." Annu Rev Ecol Syst 23: 175-200.

Whitmill, L. and P. Floor (1992). "Joint Global Positioning System--aerial triangulation project final project report." Eng Field Notes U S Dep Agric For Serv Eng Staff 24: 35-44.

Wolfe, M. L. (1992). "GIS-assisted input data set development for the Finite Element Storm Hydrograph Model (FESHM)." Appl Eng Agric 8(2): 221-227.
A study was conducted to develop an automated proceedings to assist in the development of input data sets for the FESHM hydrologic model using the GRASS geographic information system. Shell scripts (executable sequences of commands in the UNIX operating system) were developed to overlay soils and land use maps to generate hydrologic response unit (HRU) maps and to compute the fractional areas of HRUs in overland flow elements. The automated procedures decreased the input data set development time significantly, by approximately 250% (from five to two hours) for a 122 ha (303 ac) watershed. The time savings on larger, more variable watersheds would be even greater. The input data set development procedure provides an efficient manner for considering alternative land use and management scenarios.

Yarie, J. A. (1992). "Geographic Information Systems (GIS)." Agroborealis Alaska Agric For Exp Stn Univ Alaska Fairbanks 24(1): 49.

Zeiler, M. N. (1992). "Integrating GIS and GPS for mapping and analysis of electric distribution circuits." Pap Presented Annu Conf Rural Electr Power Conf(36): D2/1-D2/10.

(1993). Proceedings of the Twenty-Fifth International Symposium on Remote Sensing and Global Environmental Change : tools for sustainable development, 4-8 April 1993, Graz, Austria. Ann Arbor, Mich., Environmental Research Institute of Michigan, c1993 2 v. (xxi, 773; xxi, 929 p.) : ill.

(1993). Estimated potential yield of water wells, Sierra and Socorro counties, New Mexico : February 1993. Fort Worth, TX, USDA, SCS, National Cartography & GIS Center ; [Albuquerque, N.M. : State Conservationist, distributor], 1993. 1 map : col.

Bashford, L. L. (1993). "External flute seed metering evaluation related to site specific farming." Pap Am Soc Agric Eng(93-8517): 15.

Benedetti, R. and P. Rossini (1993). "On the use of NDVI profiles as a tool for agricultural statistics: the case study of wheat yield estimate and forecast in Emilia Romagna." Remote Sensing Environ 45(3): 311-326.

Blinn, C. R., L. P. Queen, et al. (1993). Geographic information systems : a glossary. St. Paul, MN, Minnesota Extension Service, University of Minnesota, 1993. 12 p. : ill., maps.

Brewer, C. D. (1993). The use of Landsat Thematic Mapper and geographic information systems in the detection and assessment of forest damage occurring in the Krkonse National Park. 1993. x, 85 leaves, ill. (some col.), maps.

Chu, Y. T., S. R. Archer, et al. (1993). "Spatial modeling of succession in a subtropical savanna." PR Tex Agric Exp Sta(5047): 27.

Confer, J. J., A. R. Graefe, et al. (1993). "A geographic information systems approach to analysis of the spatial relationships between recreational boating uses and perceived impacts." Gen tech rep NE(176): 103-110.

Creech, D. L. and D. McDonald (1993). "Geographic information systems: a conservation tool." Public gard 8(6): 18-20, 36.

Engel, B. A., R. Srinivasan, et al. (1993). "Nonpoint source (NPS) pollution modeling using models integrated with geographic information systems (GIS)." Water sci technol 28(3/5): 685-690.

Everitt, J. H., D. E. Escobar, et al. (1993). "Integration of airborne video, global positioning system and geographic information system technologies for detecting and mapping two woody legumes on rangelands." Weed technol 7(4): 981-987.

Falconer, A. (1993). Mapping tomorrow's resources : a symposium on the uses of remote sensing, geographic information systems (GIS) and global positioning systems (GPS) for natural resources management. Logan, Utah, Utah State University, College of Natural Resources, 1993. vii, 87 p. : ill., maps.

Gagnon, P. A., J. P. Agnard, et al. (1993). "Evaluation of a soft-copy photogrammetry system for tree-plot measurements." Can j for res 23(9): 1781-1785.
This article describes and evaluates the application of a soft-copy photogrammetry system to large-scale forest inventories. A specially designed software, developed by the authors, has been investigated in terms of accuracy and general operability. Tests based on 1:1100 color aerial photographs, taken with a 10-m cross-boom system and digitized at resolutions of 300, 450, and 600 dots per inch, confirmed the expected tree-height accuracies of 48, 32, and 24 cm, respectively. This indicates that a photographic scale of 1:800 and a scanning resolution of 800 dots per inch could produce a tree-height precision of the order of 10 cm. The tests have shown that model orientation takes about 15 min; for a tree plot of 24 trees, measurements (height and crown diameter) and observations (species and condition) also take about 15 min. As the important problem of positioning a helicopter over a tree plot has now been solved using global positioning system receivers. the results and information presented in this paper indicate that the existing technology can provide a rigorous and operational photogrammetric system for large-scale forest inventories and regeneration monitoring.

Ghabour, T. K. and M. Antrop (1993). "Low-cost geographic information systems (GIS) for land use evaluation."

Goodchild, M. F., B. O. Parks, et al. (1993). Environmental modeling with GIS. New York, Oxford University Press, 1993. xxiii, 488 p., [8] p. of plates : ill., maps.

Graham, L. A. (1993). "Airborne video for near-real-time vegetation mapping." J For 91(8): 28-32.

Haines Young, R. H., D. R. Green, et al. (1993). Landscape ecology and geographic information systems. London ; New York, Taylor & Francis, 1993. ix, 288 p. : ill., maps.

Harlin, J. M. and K. J. Lanfear (1993). Proceedings of the Symposium on Geographic Information Systems and Water Resources. Bethesda, Md., American Water Resources Association, c1993. xvi, 640 p. : ill. (some col.), maps (some col.).

Harrison, J. D., S. C. Borgelt, et al. (1993). "Applications of global positioning system technology at the Missouri MSEA."

He, C., J. F. Riggs, et al. (1993). "Integration of geographic information systems and a computer model to evaluate impacts of agricultural runoff on water quality." Water resour bull 29(6): 891-900.
This study integrates an Agricultural Non-Point Source Pollution Model (AGNPS), the Geographic Resource Analysis Support System (GRASS) (U.S. Army Corps of Engineers, 1987), and GRASS WATERWORKS (a hydrologic modeling tool box being developed at the Michigan State University Center for Remote Sensing) to evaluate the impact of agricultural runoff on water quality in the Cass River, a subwatershed of Saginaw Bay. AGNPS is used to estimate the amounts, origin, and distribution of sediment, nitrogen (N), and phosphorus (P) in the watershed. GRASS and GRASS WATERWORKS are used to generate parameters needed for AGNPS from digital maps, which include soil association, land use, watershed boundaries, water features, and digital elevation. Outputs of the model include spatially distributed estimates of volume and peak runoff, overland and channel erosion, sediment yields, and concentrations of nitrogen and phosphorus. Management scenarios are explored in the AGNPS model to minimize sedimentation and nutrient loading. Scenarios evaluated include variations in crop cover, tillage methods, and other agricultural management practices. In addition, areas vulnerable to erosion are identified for best management practices.

Hurn, J. (1993). Differential GPS explained : an expose of the surprisingly simple principles behind today's most advanced positioning technology. Sunnyvale, CA, Trimble Navigation, c1993. 55 p. : ill.

Jameson, D. A. (1993). "Historic, current and possible future analytical capabilities of geographic information systems (GIS)." Gen Tech Rep NE U S Dep Agric For Serv Northeast For Exp Stn(175): 1-7.

Jasumback, T. (1993). "Evaluating GPS in a dense tree canopy." Eng field notes 26, i.e. 25: 43-51.

Keating, J. B. (1993). The geo-positioning selection guide for resource management. Cheyenne, WY, Bureau of Land Management, [1993] vi, 64 p. : ill., maps.

Kovar, K. and H. P. Nachtnebel (1993). Application of geographic information systems in hydrology and water resources management : proceedings of an international conference held in Vienna, Austria, from 19 to 22 April 1993 : this conference was jointly organized by the International Commission on Groundwater of the International Association of Hydrological Sciences (IAHS), the United Nations Educational, Scientific and Cultural Organization (UNESCO) - as a contribution to subprogramme M-2-3 of UNESCO's IHP-IV, Universitat fur Bodenkultur, Vienna. Wallingford, International Association of Hydrological Sciences, 1993. xi, 693 p. : ill., maps.

Lance, K. (1993). "Bringing technology down to earth: a GPS consumer's guide." J For 91(8): 17-19.

Lass, L. W. and R. H. Callihan (1993). "GPS and GIS for weed surveys and management." Weed technol 7(1): 249-254.

Maclean, A. L., T. P. D'Avello, et al. (1993). "The use of variability diagrams to improve the interpretation of digital soil maps in a GIS." Photogramm Eng Remote Sensing 59(2): 223-228.

McCauley, J. D., B. A. Engel, et al. (1993). "Assessing the spatial variability of organic matter." Pap Am Soc Agric Eng(93-1531/93-1560): 14.

Myhre, B. E. and S. F. Shih (1993). "Using SPOT satellite data and geographic information systems for agriculture and silviculture land-use inventories." Proc Soil Crop Sci Soc Fla 52: 121-126.

Neldner, V. J. (1993). Vegetation survey and mapping in Queensland : its relevance and future, and the contribution of the Queensland Herbarium. Brisbane, Queensland Dept. of Environment and Heritage, 1993. v, 71 p. : maps.

Pijanowski, B. C. (1993). An inventory of geographic information system (GIS) use in USDA : USDA Global Change Data Assessment and Integration Project. University Center, MI, The Consortium, [1993] 1 v. (various foliations) : ill.

Prather, T. S. and R. H. Callihan (1993). "Weed eradication using geographic information systems." Weed technol 7(1): 265-269.

Queen, L. P. and C. R. Blinn (1993). The basics of geographic information systems. St. Paul, MN, Minnesota Extension Service, University of Minnesota, 1993. 15 p. : ill.

Singh, U. (1993). Linking crop models with a geographic information system to assist decisionmaking : a prototype for the Indian semiarid tropics. Muscle Shoals, Ala., U.S.A., International Fertilizer Development Center, 1993. iii, 39 p. : ill., maps (some col.).

Smith, P. A. and H. D. Scott (1993). "Use of GIS to rank counties for potential groundwater pollution." Ark farm res 42(2): 4-5.

Stroh, J., S. R. Archer, et al. (1993). "Assessing the influence of subsoil heterogeneity on vegetation patterns in the Rio Grande Plains of southern Texas using electromagnetic induction and geographic information systems." PR Tex Agric Exp Sta(5047): 39-42.

Trichilo, P. J., L. T. Wilson, et al. (1993). "Use of geographic information systems to assess risk of boll weevil infestations." Proc Beltwide Cotton Conf 2: 944-946.

Waite, L. A. and K. C. Thomson (1993). Development, description, and application of a geographic information system data base for water resources in karst terrane in Greene County, Missouri. Rolla, Mo., U.S. Geological Survey ; Denver, Colo. : Earth Science Information Center, Open-File Reports Section [distributor], 1993. vi, 31 p. : ill., maps (some col.).

Wilson, J. P., W. P. Inskeep, et al. (1993). "Coupling geographic information systems and models for weed control and groundwater protection." Weed technol 7(1): 255-264.

(1994). Plant materials, Minnesota, North Dakota, and South Dakota : October 1995. Rev. Dec. 1994. Ft. Worth, TX., USDA, NRCS, National Cartography & GIS Center ; [Lincoln, Neb. : Midwest National Technical Center, distributor], 1995. 1 map : col.

(1994). National GIS guidebook : Integrated Information Management Program : Geographic Information System. Washington, D.C., USDA Forest Service, Informationa Systems & Technology, [1994] 78 p. : ill., maps.

(1994). Decision making with GIS, the fourth dimension : Eighth Annual Symposium on Geographic Information Systems in forestry, environmental and natural resources management, February 21-24, 1994, Vancouver, British Columbia, Canada. Vancouver, B.C., Polaris Conferences, 1994. 2 v. : ill., maps.

Auernhammer, H., M. Demmel, et al. (1994). "GPS for yield mapping on combines." Comput electron agric 11(1): 53-68.

Bonham Carter, G. (1994). Geographic information systems for geoscientists : modelling with GIS. 1st ed. Oxford ; New York, Pergamon, 1994. xvii, 398 p. : ill. (some col.), maps (some col.).

Cahn, M. D., J. W. Hummel, et al. (1994). "Spatial analysis of soil fertility for site-specific crop management." Soil Sci Soc Am j 58(4): 1240-1248.
Spatial patterns of soil properties and nutrient concentrations need to be characterized to develop site-specific farming practices that match agricultural inputs with regional crop needs. The spatial variation of soil organic C (SOC), soil water content (SWC), NO3-N, PO4-P, and K were evaluated in the 0- to 15-cm layer of a 3.3-ha field (Typic Haplaquoll and Argiaquic Argialboll) cropped with maize (Zea mays L.) and soybean [Glycine max (L.) Merr.]. The range of spatial correlation was determined from semivariance analyses of the data and was found to vary among and within fertility parameters. Nitrate had the shortest correlation range (< 5 m) and SOC had the longest (> 180 m), whereas SWC, PO4-P, and K had intermediate spatial correlation ranges. In addition, SOC was found to have small-scale spatial variation nested within large-scale spatial variation. The spatial pattern of NO3-N changed with time. Frequency distributions of SOC and SWC were close to normal, whereas the distributions of NO3-N, K, and PO4-P data were skewed. Median polishing detrending and trimming of outlying data were useful methods to remove the effects of nonstationarity and non-normality from the semivariance analysis. The results suggest that reducing sampling intervals from 50 to 1 m would reduce the variance of SWC, SOC, NO3-N, PO4-P, and K estimates by 74, 95, 25, 64, and 58%, respectively. A useful sampling pattern for characterizing the spatial variation of several soil properties-nutrients and scales should be random with sample spacing as close as 1 m and as far apart as the longest dimension of the field.

Coop, L. B., B. A. Croft, et al. (1994). "Geographic information systems and simulation in regional orchard management: pesticide resistance in Hood River Valley, Oregon." Acta hortic(367): 383-390.

Dvorak, J. (1994). Global Positioning System measurements on the Island of Hawaii from 1987 to 1990. Washington, D.C., U.S. G.P.O. ; Denver, CO : For sale by U.S. Geological Survey, Map Distribution, 1994. iv, 33 p. : ill., maps.

Everitt, J. H., D. E. Escobar, et al. (1994). "Using airborne video, global positioning system, and geographical information system technologies for detecting and mapping citrus blackfly infestations." Southwest entomol 19(2): 129-138.

Farrar, T. J., S. E. Nicholson, et al. (1994). "The influence of soil type on the relationships between NDVI, rainfall, and soil moisture in semiarid Botswana. II. NDVI response to soil moisture." Remote sens environ 50(2): 121-133.

Garten, C. T., Jr., M. A. Huston, et al. (1994). "Topographic variation of soil nitrogen dynamics at Walker Brance Watershed, Tennessee." For sci 40(3): 497-512.
Understanding the spatial and temporal variability of soil nitrogen (N) transformations is central to quantifying the N dynamics and productivity of ecosystems. The objectives of this work were to examine spatial and temporal variation of soil N dynamics and to identify factors correlated with topographic variation in soil N dynamics in a forest watershed. Net N mineralization and net nitrification potential were measured by aerobic laboratory incubations of surface (0-7 cm) mineral soils. Principal components analysis was used to describe sampling sites across the watershed based on 13 site characterization variables. A topographic index used in hydrologic modeling, In (alpha/tan beta), was calculated for each site as the natural logarithm of the ratio of the up slope drainage area per unit contour length (alpha) to the local slope angle (tan beta). Soils from valley floors had greater total N concentrations, lower carbon-to-nitrogen (C:N) ratios, greater potential net nitrification, and greater microbial activity (as indicated by short-term urease assays) than soils from ridges. Mean net nitrification potential was 0.59 micrograms N g-1 d-1 in surface soils from valley floors and was < 0.01 on ridges and slopes. The first principal component was related to the N and C properties of soils, leaf litter, and leaf fall at a site. The second principal component was related to forest stand composition. The topographic index was significantly correlated with important variables related to soil N dynamics. Once calibration data are derived, this index may be useful as a first approximation to total soil N concentrations and soil C:N ratios in forest watersheds because.

Goodchild, M. F. (1994). "Integrating GIS and remote sensing for vegetation analysis and modeling: methodological issues." J veg sci 5(5): 615-626.

Guyot, G. and X. Gu (1994). "Effect of radiometric corrections on NDVI-determined from SPT-HRV and Landsat-TM data." Remote sens environ 49(3): 169-180.

Hosseini, E., J. Gallichand, et al. (1994). "Theoretical and experimental performance of spatial interpolation methods for soil salinity analysis." Trans ASAE 37(6): 1799-1807.
Interpolation methods are required for analysis of soil salinity data by geographic information systems. This study was conducted to determine interpolation methods that are best suited to map soil salinity. Methods of closest neighbor, kriging, inverse-distance moving average, and thin plate smoothing splines were compared by cross-validation for precision and smoothing, using 341 measured values of electrical conductivity of saturated paste extract in a 16000 ha area in southwest Iran. Interpolation precision of all methods were low, with a mean absolute difference between measured and predicted values ranging from 42 to 76% of the mean measured soil salinity. This was due to the large ratio of nugget effect to the sill of the variogram and to the high variability of data. Thin plate smoothing splines and ordinary kriging were the most precise methods, whereas closest neighbor was the least precise. The smoothing of the methods was assessed by comparing the dispersion standard deviation of interpolated values with that of observed values. The most precise methods were also those that performed an important smoothing. Ordinary kriging and thin plate smoothing splines produced contour maps that were much easier to interpret. A theoretical analysis of the performance of the methods (precision and smoothing) led to conclusions similar to those based on the cross-validation study. Such a theoretical analysis can be used to select an appropriate interpolation method without the need for time consuming cross-validation.

Ikehara, M. E. and S. P. Phillips (1994). Determination of land subsidence related to ground-water-level declines using Global Positioning System and leveling surveys in Antelope Valley, Los Angeles and Kern Counties, California, 1992. Sacramento, Calif., U.S. Dept. of the Interior, U.S. Geological Survey ; Denver, CO : For sale by the U.S. Geological Survey, Earth Science Information Center, Open-File Reports Section], 1994. vi, 101 p. : ill., maps.

Larsen, W. E., G. A. Nielsen, et al. (1994). "Precision navigation with GPS." Comput electron agric 11(1): 85-95.

Macy, T. S., D. L. Thackery, et al. (1994). "Yield monitoring experiences--1994." Pap Am Soc Agric Eng(94-1576/94-1587): 15.

McKimmey, J. M. (1994). Predicting sediment and phosphorus sources in the Beaver Reservoir watershed using a geographic information system. 1994 xi, 166 leaves, ill., maps (some col.).

Michaelsen, J., D. S. Schimel, et al. (1994). "Regression tree analysis of satellite and terrain data to guide vegetation sampling and surveys." J veg sci 5(5): 673-686.

Mohanty, B. P., U. S. Tim, et al. (1994). "Impacts of agricultural drainage well closure on crop production: a watershed case study." Water resour bull 30(4): 687-703.
Much of north-central Iowa is characterized by flat topography, shallow depressions, and poor natural surface drainage. Land drainage systems comprising of tile drains and agricultural drainage wells (ADWs) are used as outlets for subsurface drainage of cropland under corn and soybean production. Studies have shown that these drainage systems, mainly the ADWs, are potential routes for agricultural chemicals to underground aquifers. To protect the region's vital groundwater resource, researchers are evaluating alternative outlets ranging from complete closure of existing ADWs (and creation of wetlands) to continued use of ADWs and chemical management in a comprehensive policy framework. This paper presents the results of a study designed to provide government jurisdictions, farmers, and land managers information for assessing the impact of closing ADWs on crop production. The study couples a geographic information systems database for a 471-hectare watershed in Humboldt County, Iowa, with a groundwater flow model (MODFLOW) and an empirical crop yield loss model to predict long-term effects of complete closure of ADWs on crop production. The cropland areas inundated and the relative crop yield loss due to ADW closure are determined as a function of long-term climatic data. The results indicate that elimination of drainage outlets in the watershed could result in ponding of low-lying areas and poorly drained soils, making them unsuitable for crop production. Such wetness also decreases the efficiency of production in the no-ponding areas by isolating fields, and the crop yield loss can be reduced by an annual average of about 18 percent.

Myers, R. L. (1994). "Identifying suitable regions for amaranth production using a geographic information systems approach." Am J altern agric 9(3): 122-126.
Amaranth is an alternative grain crop that shows significant promise in the U.S. A geographic information system (GIS) was used to analyze the most suitable regions for growing amaranth in Missouri GIS software provides tools to manipulate and display geographically based information, in this case the factors affecting amaranth's suitability. Of several such factors considered, the ones used were soils, rainfall, sorghum production, disease potential, and labor availability. Soil, rainfall, and disease information were assumed to be direct factors in yield potential. Current sorghum production areas were considered likely areas for amaranth production, given the similarities between the crops. Labor availability also was assumed to affect adoption, since amaranth requires more labor than traditional grain crops. The analysis showed that central and southeastern Missouri would be the most favorable areas for amaranth production. Other suitable areas are along the Mississippi and Missouri river valleys and in western Missouri. This GIS approach can be modified to include additional factors and refinements, and could be used with other alternative crops or for other regions of the country.

Myneni, R. B. and D. L. Williams (1994). "On the relationship between FAPAR and NDVI." Remote sens environ 49(3): 200-211.

Neilson, R. P. and D. Marks (1994). "A global perspective of regional vegetation and hydrologic sensitivities from climatic change." J veg sci 5(5): 715-730.

Nelson, M. R., R. Felix Gastelum, et al. (1994). "Geographic information systems and geostatistics in the design and validation of regional plant virus management programs." Phytopathology 84(9): 898-905.
A regional management plan was designed and implemented for a multi-virus, multivector, disease complex in tomatoes in the Del Fuerte Valley, Sinaloa, Mexico. The viruses include tobacco etch and cucumber mosaic with aphid vectors, a geminivirus complex with whitefly vectors, tomato spotted wilt with thrips vectors, and tomato mosaic with no known vector. Although the viruses and their vectors are biologically diverse, all are transmitted by flying insects, with the exception of tomato mosaic, and all except tomato mosaic are known to have alternate hosts among weeds and other crop plants in the area. Because of these similarities, we developed a risk-assessment process based on general virus infection hazards rather than specific viruses. The risk assessment helped to focus on actions that could be taken both locally and regionally to reduce early and damaging infections. Risk assessment and virus disease-incidence data were collected from 53 fields during 1990-1991 and 60 fields during 1991-1992. A geostatistical analysis of risk and incidence showed that both were spatially dependent variables with a variogram range of 20 to 25 km. Moving spatial averages (computed by kriging) indicated that the area east of Los Mochis was higher in risk and incidence than the area near Guasave during both seasons. Qualitative observations consistent with observed patterns of incidence suggest there are underlying landscape features more conducive to endemic plant virus diseases in the Los Mochis area than in the Guasave area.

Nicholson, S. E. and T. J. Farrar (1994). "The influence of soil type on the relationships between NDVI, rainfall, and soil moisture in semiarid Botswanna. I. NDVI response to rainfall." Remote sens environ 50(2): 107-120.

Obermeyer, N. J. and J. K. Pinto (1994). Managing geographic information systems. New York, Guilford Press, c1994. xiii, 226 p. : ill.

Papajorgji, P., J. W. Jones, et al. (1994). "Using crop models and geographic information systems to study the impact of climate change in the southeastern USA." Proc Soil Crop Sci Soc Fla 53: 82-86.

Perez Munoz, F. and T. S. Colvin (1994). "Continuous grain yield monitoring." Pap Am Soc Agric Eng(94-1039/94-1074): 11.

Reed, B. C., J. F. Brown, et al. (1994). "Measuring phenological variability from satellite imagery." J veg sci 5(5): 703-714.

Rutchey, K. and L. Vilcheck (1994). "Development of an Everglades vegetation map using a SPOT image and the Global Positioning System." Photogramm eng remote sensing 60(6): 767-775.

Salute, J., C. Bell, et al. (1994). "The use and transfer of remote sensing and geographic information systems technology to detect phylloxera stress in vineyards, early results." Proc Technol Transf Soc Annu Meet Int Symp exhib(19th): 54-60.

Sample, V. A. (1994). Remote sensing and GIS in ecosystem management. Washington, D.C., Island Press, c1994. xiii, 369 p. : ill., maps.

Schueller, J. K. and M. W. Wang (1994). "Spatially-variable fertilizer and pesticide application with GPS and DGPS." Comput electron agric 11(1): 69-83.

Sombroek, W. G. and J. Antoine (1994). "The use of geographic information systems (GIS) in land resources appraisal." Outlook agric 23(4): 249-255.

Srinivasan, R. and B. A. Engel (1994). "A spatial decision support system for assessing agricultural nonpoint source pollution." Water resour bull 30(3): 441-452.
A spatial decision support system (SDSS) was developed to assess agricultural nonpoint source (NPS) pollution using an NPS pollution model and geographic information systems (GIS). With minimal user interaction, the SDSS assists with extracting the input parameters for a distributed parameter NPS pollution model from user-supplied GIS base layers. Thus, significant amounts of time, labor, and expertise can be saved. Further, the SDSS assists with visualizing and analyzing the output of the NPS pollution simulations. Capabilities of the visualization component include displays of sediment, nutrient, and runoff movement from a watershed. The input and output interface techniques/algorithms used to develop the SDSS, along with an example application of the SDSS, are described.

Stafford, J. V. and B. Ambler (1994). "In-field location using GPS for spatially variable field operations." Comput electron agric 11(1): 23-36.

Stephen, R. M. (1994). "Micronutrient focus in modern farming." Proc annu meet Fert Ind Round Table(44th): 62-65.

Taupier, R. and C. Willis (1994). "Geographic information systems and applied economics: an initial discussion of potential applications and contributions." Agric resour econ rev 23(2): 140-149.

Tim, U. S. and R. Jolly (1994). "Evaluating agricultural nonpoint-source pollution using integrated geographic information systems and hydrologic/water quality model." J environ qual 23(1): 25-35.
Considerable progress has been made in developing physically based, distributed parameter, hydrologic/water quality (H/WQ) models for planning and control of nonpoint-source pollution. The widespread use of these models is often constrained by the excessive and time-consuming input data demands and the lack of computing efficiencies necessary for iterative simulation of alternative management strategies. Recent developments in geographic information systems (GIS) provide techniques for handling large amounts of spatial data for modeling nonpoint-source pollution problems. Because a GIS can be used to combine information from several sources to form an array of model input data and to examine any combinations of spatial input/output data, it represents a highly effective tool for H/WQ modeling. This paper describes the integration of a distributed-parameter model (AGNPS) with a GIS (ARC/INFO) to examine nonpoint sources of pollution in an agricultural watershed. The ARC/INFO GIS provided the tools to generate and spatially organize the disparate data to support modeling, while the AGNPS model was used to predict several water quality variables including soil erosion and sedimentation within a watershed. The integrated system was used to evaluate the effectiveness of several alternative management strategies in reducing sediment pollution in a 417-ha watershed located in southern Iowa. The implementation of vegetative filter strips and contour buffer (grass) strips resulted in a 41 and 47% reduction in sediment yield at the watershed outlet, respectively. In addition, when the integrated system was used, the combination of the above management strategies.

Wallace, A. (1994). "High-precision agriculture is an excellent tool for conservation of natural resources." Commun soil sci plant anal 25(1/2): 45-49.

Walsh, S. J. and F. W. Davis (1994). "Applications of remote sensing and geographic information systems in vegetation science: introduction." J veg sci 5(5): 610-613.

White, J. D. and S. W. Running (1994). "Testing scale dependent assumptions in regional ecosystem simulations." J veg sci 5(5): 687-702.

Zuydam, R. P. v. and C. Sonneveld (1994). "Test of an automatic precision guidance system for cultivation implements." J agric eng res 59(4): 239-243.

(1995). Proceedings of the Seminar on Site Specific Farming, Koldkoergaard, Aarhus. March 20-21, 1995. Lyngby [Denmark], Landbrugsministeriet, Statens planteavlsforsog, 1995. 204 p. : ill.

Battaglin, W. A. and D. A. Goolsby (1995). Spatial data in geographic information system format on agricultural chemical use, land use, cropping practices in United States. Denver, Colo., U.S. Dept. of the Interior, U.S. Geological Survey ; Denver, CO : Earth Science Information Center, Open-File Reports Section [distributor], 1995. iv, 87 p. : col. maps.

Bojorquez Tapia, L. A., I. Azuara, et al. (1995). "Identifying conservation priorities in Mexico through geographic information systems and modeling." Ecol appl 5(1): 215-231.

Burgess, D. W., P. Lewis, et al. (1995). "Topographic effects in AVHRR NDVI data." Remote sens environ 54(3): 223-232.

Christensen, L. and K. Krause (1995). "Precision farming: harnessing technology." Agric outlook(218): 18-19.

D'Eon, S. P. (1995). "Accuracy and signal reception of a hand-held Global Positioning System (GPS) receiver." For chron 71(2): 192-196.
Accurate and precise reporting of forest survey locations is required to integrate forest survey data with Geographical Information Systems. The accuracies of five Global Positioning System (GPS) survey methods using a hand-held receiver were tested in a mixed forest of trembling aspen and spruce. Accuracy improved by eliminating positions obtained under poor satellite configurations and by using position averaging methods. Single fix positions, taking as little as two minutes to obtain, yielded better than 100m accuracy more than 80% of the time. Allowing the receiver to continuously collect fixes for 15 to 30 minutes and then averaging the fixes yielded a median position error of 17 m. Sixty one stands representing a diversity of cover types, canopy heights, and crown closure in the Petawawa Research Forest were tested during June and July of 1992 for canopy interference with GPS signals. A GPS position was obtained under the canopy in 74% of the stands. Launches of additional GPS satellites since the summer of 1992 have further improved the probability of obtaining accurate geographical positions under forest canopies.

D'Erchia, F. (1995). Geographic information systems and remote sensing applications for ecosystem management. Rev. Dec. 1995. Onalaska, Wis., National Biological Survey, Environmental Management Technical Center ; [Springfield, Va. : National Technical Information Service, distributor], 1995. vi, 23 p. : ill., maps.

Doolittle, J., E. Ealy, et al. (1995). "Reconnaissance soil mapping of a small watershed using electromagnetic induction and global positioning system techniques." Soil surv horiz 36(3): 86-94.

Epiphanio, J. C. N. and A. R. Huete (1995). "Dependence of NDVI and SAVI on sun/sensor geometry and its effect on fAPAR relationships in alfalfa." Remote sens environ 51(3): 351-360.

Fraser, R. H., M. V. Warren, et al. (1995). "Comparative evaluation of land cover data sources for erosion prediction." Water resour bull 31(6): 991-1000.
A fundamental problem in protecting surface drinking water supplies is the identification of sites highly susceptible to soil erosion and other forms of nonpoint source (NPS) pollution. The New York City Department of Environmental Protection is trying to identify erodible sites as part of a program aimed at avoiding costly filtration. New York City's 2,000 square mile watershed system is well suited for analysis with geographic information systems (GIS); an increasingly important tool to determine the spatial distribution of sensitive NPS pollution areas. This study used a GIS to compare three land cover sources for input into the Modified Universal Soil Loss Equation (MUSLE), a model estimating soil loss from rangeland and forests, for a tributary watershed within New York City's water supply system. Sources included both conventional data (aerial photography) and Landsat data (MSS and TM images). Although land cover classifications varied significantly across these sources, location-specific and aggregate watershed predictions of the MUSLE were very similar. We conclude that using Landsat TM imagery with a hybrid classification algorithm provides a rapid, objective means of developing large area land cover databases for use in the MUSLE, thus presenting an attractive alternative to photo interpretation.

Friedl, M. A., F. W. Davis, et al. (1995). "Scaling and uncertainty in the relationship between the NDVI and land surface BIOPHYSICAL variables: an analysis using a scene simulation model and data from FIFE." Remote sens environ 54(3): 233-246.

Harrigan, J. (1995). GIS Geographic informatiton systems : improving local decision making. Los Osos, CA, San Luis Video Publishing, [1995?]. 1 videocassette (28 min., 30 sec.) : sd., col.
Shows what GIS is, why it's useful, and what it can do. Helpful in the process of making land use decisions, etc.

Hashmi, M. A., L. A. Garcia, et al. (1995). "Spatial estimation of regional crop evapotranspiration." Trans ASAE 38(5): 1345-1351.
Current methods of computing regional crop evapotranspiration (ET), the prime variable in estimating irrigation demand, largely ignore the spatial variability of ET parameters, thus introducing errors. In this research, a method was developed to estimate regional ET while considering the spatial variability of parameters. To consider this variability, spatial databases were developed for agricultural land-use, relevant climatic parameters, and topographic data using geographic information systems (GIS). Analytical GIS functions of map algebra and map overlay were used to calculate regional crop ET for the Cache la Poudre Basin in Colorado. The Cache la Poudre Basin was selected as the study area due to the availability of ground truthed land-use survey data. This research uses land-use classification, climatic variables and elevation adjustments to determine the value of using a spatial/GIS approach instead of current nonspatial approaches.

Johnson, D. R., C. D. Klein, et al. (1995). "Role of global positioning technology in surveying fall and spring boll weevil populations in Arkansas." Proc Beltwide Cotton Conf 2: 800-801.

Kenna, M. P. (1995). "Detecting turf stress with remote sensing." Grounds maint 30(10): G17-G20.

Kernodle, J. M., D. P. McAda, et al. (1995). Simulation of ground-water flow in the Albuquerque Basin, central New Mexico, 1901-1994, with projections to 2020. Albuquerque, N.M., U.S. Dept. of the Interior, U.S. Geological Survey ; Denver, Colo. : Earth Science Information Center, Open-File Reports Section [distributor], 1995. ix, 114 p. : ill., maps (some col.).

Kleene, J. W. (1995). Watershed nonpoint source management system : a geographic information system approach. 1995. xiv, 333 leaves, ill.

Larson, T. (1995). "Requirements for a fully integrated fertilizer program." Proc annu meet Fert Ind Round Table(45th): 52-57.

Menenti, M., S. Azzali, et al. (1995). "Fourier analysis of time series of NOAA-AVHRR NDVI composites to map isogrowth zones." Stud environ sci(65A): 425-430.

Ollinger, S. V. (1995). Modeling physical and chemical climate of the Northeastern United States for a geographic information system. Radnor, PA, U.S.Dept. of Agriculture, Forest Service, Northeastern Forest Experiment Station, [1995] 30 p. : ill., col. maps.

Parish, R. L., D. B. Reynolds, et al. (1995). "Precision-guided cultivation techniques to reduce herbicide inputs in cotton." Appl eng agric 11(3): 349-353.
Cotton farmers in the Mississippi River Delta area typically apply preemergence and directed post emergence herbicides to a 400 to 500 mm (16 to 20 in.) band over the row, and then cultivate the middles without getting very close to the row. This project demonstrates that farmers can reduce the band width to 200 mm (8 in.) and then cultivate close to the row using precision-guided cultivators. Using this method, herbicide costs were reduced $30.22/ha ($12.23/acre) in 1992 and $27.80/ha ($11.25/acre) in 1993 with no differences in weed control or loss of yield. The total cost reduction taking into account the costs of cultivation and application was $25.60/ha ($10.36/acre) in 1992 and $25.77/ha ($10.43/acre) in 1993. Reducing the amount of herbicide used also reduces environmental risks. The precision guidance systems are affordable and easy to use.

Petersen, G. W., J. C. Bell, et al. (1995). "Geographic information systems in agronomy." Adv agron 35: 67-111.

Ramsey, R. D., A. Falconer, et al. (1995). "The relationship between NOAA-AVHRR NDVI and ecoregions in Utah." Remote sens environ 53(3): 188-198.

Theocharopoulos, S. P., D. A. Davidson, et al. (1995). "Soil survey and geographic information systems technology." Soil surv horiz 36(1): 1-4.

Usery, E. L., S. Pocknee, et al. (1995). "Precision farming data management using geographic information systems." Photogramm eng remote sensing 61(11): 1383-1391.

Valentine, T. (1995). "Aerial detection surveys and geographic information systems." Rep US For Serv North Reg Timber Coop For Pest Manag(95-4): 7-8.

Vetter, A. A. (1995). "Quantitative evaluation of DGPS guidance for ground-based agricultural applications." Appl eng agric 11(3): 459-464.
The Global Positioning System (GPS) satellites provide positioning information which can be of significant use for agricultural applicators. This article presents the results of a quantitative evaluation of the precision of a commercial device which incorporates differentially corrected GPS signals (DGPS) to guide a ground vehicle along swaths. The precision of the cross-track displacement along the swath is determined with a video camera verification system and the results have been analyzed statistically. The quantitative tests have shown excellent cross track precision. For an automobile traveling at an average speed of 19 m/s over a total test distance of 23 km, the standard deviation from the unmarked centerline was 0.42 m. The 50 and 90 percentile distances from the centerline were 0.39 and 0.98 m, respectively.

Watkins, R. L. (1995). Land suitability for viticulture : a geographic information system-derived method for a Mediterranean type climate in California. 1995. ix, 132 leaves, ill.

Wittich, K. P. and O. Hansing (1995). "Area-averaged vegetative cover fraction estimated from satellite data." Int j biometeorol 38(4): 209-215.
The relationship was analysed between the vegetation cover factor expressed as a percentage and the area-averaged normalized difference vegetation index (NDVI). On selected days the NDVI was calculated from channel 1 and 2 reflectance data of the National Oceanic and Atmospheric Administration (NOAA-11) satellite's advanced very high-resolution radiometer (AVHRR) for five test areas under agricultural and forestry use. No ground-based reflectance measurements could be made for validation of these data. Therefore the land surface NDVI, which varied with time, and percentage vegetation cover of the test areas were deduced from time-independent but site-specific statistical land use data updated by temporal phenological observations, and from surface specific reflectance curves published in the literature. The result indicated that the area-averaged NDVI, as obtained from the NOAA-11 radiometer, was less than the value calculated from the land surface NDVI. After correction to reduce the offset of the data, the values would be a suitable indicator of the fraction of vegetation cover.

Zuydam, R. P. v., C. Sonneveld, et al. (1995). "Weed control in sugar beet by precision guided implements." Crop prot 14(4): 335-340.
A field experiment was carried out in sugar beet with a wide-span (12.2 m) tractor and laser guided implements. By means of a side-shift facility, implements were mounted on this vehicle for seedbed preparation, drilling, fertilizing, spraying and hoeing. Automatic laser guidance was possible with an accuracy of 0.6 cm on a track length of 220 m on arable land. No inputs (soil cultivation, fertilizer, herbicide) were made at places where they were not needed, or even would potentially pollute the environment. The aim of the experiment, which was carried out in 2 successive years on fields of the same farm, was to investigate the influence on weed occurrence and efficiency of weed control. Leaving out seedbed preparation between the future crop rows left already germinated weeds alive. In 1 year pre-emergence application of paraquat-diquat was necessary to stop growing of well developed weed plants. A crumbling operation had to be carried out to break the clods, otherwise inter-row hoeing was impossible. From the viewpoint of weed control restricting seedbed preparation to the future sugar beet rows was not of advantage. Precision guidance allowed enlargement of mechanical weed control, i.e. inter row hoeing to 80% (40 cm wide at a row distance to 50 cm). Savings on herbicides were 75%, because little overlap was necessary of chemically and mechanically treated areas. The absence of fertilizers in these inter-row bands did not diminish the number of weeds, and speed of emergence of weeds. The effect of seedbed preparation and drilling the sugar beet crop in complete darkness (at night), made possible by the automatic guidance, on weed infestation was not different from daylight treatments. In these.

(1996). Proceedings for the 26th International Symposium on Remote Sensing of Environment [and] the 18th Symposium of the Canadian Remote Sensing Society : information tools for sustainable development, March 25-29, 1996, Vancouver, B.C., Canada. [Vancouver, s.n., 1996] xxv, 632 p. : ill.

Al Hamed, S. A. I. (1996). Automatic tractor guidance system based on global positioning system. 1996. x, 185 leaves, ill.

Beisch, T., A. Akca, et al. (1996). Remote sensing and geographical information systems in land area ecology. Gottingen, Cuvillier, [1996?] 224 p. : ill., maps.

Beverly, R. B. (1996). "Video image analysis as a nondestructive measure of plant vigor for precision agriculture." Commun soil sci plant anal 27(3/4): 607-614.
Precision agriculture addresses spatial variability across a field in order to optimize application of fertilizer and other inputs on a site-specific basis. Soil testing provides predictive information on patterns in soil fertility and other soil conditions, but plant vigor provides a more direct and integrative indication of plant response to soil properties and management. Spatial patterns in plant vigor also provide greater resolution of soil effects than is practical using soil testing. This paper describes recent experience in applying video image analysis in monitoring plant growth (i.e., percent ground cover) as an index of vigor in field situations. Using off-the-shelf technology, video images are recorded, digitized using an image capture computer board, then measured for percent ground cover using image analysis software. Results demonstrate that video image analysis is rapid and economical and can be used to detect patterns to guide subsequent soil sampling and mapping.

Beverly, R. B. (1996). "Evaluation of the moisture equivalent soil test for irrigation management." Commun soil sci plant anal 27(3/4): 615-621.
Previous research demonstrated that the moisture equivalent (ME) soil test measured at about -80 kPa reflects soil clay and organic matter contents, exhibits good precision, and is well correlated to the -33 kPa pressure plate estimate of field capacity. However, data to guide interpretation of the ME results in irrigation management are lacking. In the present research, soil mixes comprising 45 to 100% sand, 0 to 50% clay, and 0 to 5% peat by volume were used to determine the effects of soil composition on ME measured at either -13 or -80 kpa. The plant available water capacity (AWC) was determined by growing plants in pots containing the soil mixes. Volumetric ME measurements at either -13 or -80 kPa increased linearly with clay content, as did the volumetric water content at wilting point (WP). Hence, the estimated AWC was essentially constant across the entire range tested. If WP and AWC estimates from this greenhouse study reflect field conditions, the results do not support soil testing to guide differential irrigation management based on soil texture.

Borgelt, S. C., J. D. Harrison, et al. (1996). "Evaluation of GPS for applications in precision agriculture." Appl eng agric 12(6): 633-638.
Location coordinate information is needed in precision agriculture to map in-field variability, and to serve as a control input for variable rate application. Differential global positioning system (DGPS) measurement techniques were compared with other independent data sources for sample point location and combine yield mapping operations. Sample point location could be determined to within 1 m (3 ft) 2dRMS using C/A code processing techniques and data from a high-performance GPS receiver. Higher accuracies could be obtained with carrier phase kinematic positioning methods, but this required more time and was a less robust technique with a greater potential for data acquisition problems. Data from a DGPS C/A code receiver was accurate enough to provide combine position information in yield mapping. However, distance data from another source, such as a ground-speed radar or shaft speed sensor, was needed to provide sufficient accuracy in the travel distance measurements used to calculate yield on an area basis.

Brown, T. J. and J. B. Burley (1996). "Geographic information systems in the classroom: methods and philosophies." J nat resour life sci educ 25(1): 17-25.

Burgan, R. E., R. A. Hartford, et al. (1996). Using NDVI to assess departure from average greenness and its relation to fire business. Ogden, UT, U.S. Dept. of Agriculture, Forest Service, Intermountain Research Station, [1996] 8 p. : ill., col. maps.

Cook, S. E., R. J. Corner, et al. (1996). "A rule-based system to map soil properties." Soil Sci Soc Am j 60(6): 1893-1900.
Conventional soil mapping is limited in its capabilities in that it presents a summary of the soil surveyor's conceptual view of soil variation. As such, the method conveys little regarding what is known about the variation of individual soil properties, or the quantitative nature of their variation. We developed a new method for soil mapping, based on the concepts employed in the PROSPECTOR mineral exploration system, which builds on existing soil surveyor knowledge to construct quantitative statements about individual soil properties via the development of a network of rules. These rules operate within a system of Bayesian inference to assign the varying probability of occurrence of a soil property of interest within an area, given evidence that relates to it in a known way. Permissible evidence includes the range of attributes normally used by a soil surveyor, such as landform, vegetation, land use, or parent material, and can also include remotely sensed digital data. Evidence is weighted according to the uncertainty associated with it, and combined to produce a single estimate of probability of a given attribute. The relationship between the evidence and prediction is stated explicitly at each stage of the procedure and is thus repeatable in a consistent manner. The system has the advantage that while it does not discard the evidence and knowledge used in conventional soil survey, it produces quantitative estimates of the distribution of soil properties, which can be used for a wide range of applications. The data produced is amenable to storage in geographic information systems and related data bases. As such, it can be updated or enhanced as new information or.

Corwin, D. L. and K. M. Loague (1996). Applications of GIS to the modeling of non-point source pollutants in the vadose zone. Madison, Wis., Soil Science Society of America, c1996. xxiii, 319 p., [12] p. of plates : ill. (some col.), maps (some col.).

Deckert, C. J. and P. V. Bolstad (1996). "Global Positioning System (GPS) accuracies in eastern U.S. deciduous and conifer forests." South j appl for 20(2): 81-84.
This study determined horizontal positional errors when using C/A code GPS receivers under forest canopies and in varied terrain. Positional errors were evaluated for a total of 18 sites: three sites for each of six combinations of canopy (conifer, hardwood) and terrain (ridge, slope, valley). Ten replicates were collected at each site for each of 60, 200, and 500 position fixes. Differentially corrected positional accuracies from conifer sites averaged 18.4 ft, which was significantly greater than the 14.5 ft observed for hardwood sites. For differentially corrected data, positional errors generally increased from ridgetop to valley positions. Errors decreased when the number of position fixes was increased.

Denison, R. F., A. Abshahi, et al. (1996). "Image processing extracts more information from color infrared aerial photos." Calif agric 50(3): 9-13.

Everitt, J. H., D. E. Escobar, et al. (1996). "Using spatial information technologies to map Chinese tamarisk (Tamarix chinensis) infestations." Weed sci 44(1): 194-201.
This paper describes the application of airborne video data with global positioning system and geographic information system technologies for detecting and mapping Chinese tamarisk infestations in the southwestern United States. Study areas were along the Colorado River in southwestern Arizona, the Rio Grande River in extreme west Texas, and the Pecos River in west-central Texas. Chinese tamarisk could be readily distinguished on conventional color video imagery in late November when its foliage turned a yellow-orange to orange-brown color prior to leaf drop. The integration of the global positioning system with the video imagery permitted latitude/longitude coordinates of Chinese tamarisk infestations to be recorded on each image. The global positioning system latitude/longitude coordinates were entered into a geographic information system to map Chinese tamarisk populations along the three river systems.

Gao, B. C. (1996). "NDWI--a normalized difference water index for remote sensing of vegetation liquid water from space." Remote sens environ 58(3): 257-256.

Gitelson, A. A., Y. J. Kaufman, et al. (1996). "Use of a green channel in remote sensing of global vegetation from EOS-MODIS." Remote sens environ 58(3): 289-298.

Hallam, C. A. (1996). Proceedings, AWRA Annual Symposium : GIS and water resources. Herndon, VA, The Association, c1996. x, 482 p. : ill., maps.

Harvey, C. A., D. W. Kolpin, et al. (1996). Using a geographic information system and scanning technology to create high-resolution land-use data sets. Iowa City, Iowa, U.S. Dept. of the Interior, U.S. Geological Survey ; Denver, Colo. : Branch of Information Services [distributor], 1996. iv, 41 p. : col. ill., col. maps.

Jasumback, T. (1996). Operational GPS support tech tips. Missoula, MT, U.S. Dept. of Agriculture, Forest Service, Technology & Development Program, [1996]- v. : ill.

Johnson, R. C. (1996). Target farming : a practical guide to precision agriculture. 2nd ed. [Saskatoon, SK], R.C. Johnson, c1996. 144 p. : ill. (some col.).

Kaplan, E. D. (1996). Understanding GPS : principles and applications. Boston, Artech House, c1996. xv, 554 p. : ill.

Kitchen, N. R., K. A. Sudduth, et al. (1996). "Mapping of sand deposition from 1993 midwest floods with electromagnetic induction measurements." J soil water conserv 51(4): 336-340.

Kovar, K. and H. P. Nachtnebel (1996). Application of geographic information systems in hydrology and water resources management : proceedings of the HydroGIS'96 conference held in Vienna, Austria, from 16 to 19 April 1996. Wallingford, Oxfordshire, International Association of Hydrological Sciences, 1996. xii, 711 p. : ill. (some col.), maps.

Ma, B. L., M. J. Morrison, et al. (1996). "Canopy light reflectance and field greenness to assess nitrogen fertilization and yield maize." Agron j 88(6): 915-920.
Assessment of crop N requirements is necessary to develop production systems with optimal N input. A field experiment with six maize (Zea mays L.) hybrids grown at three N fertilizer rates (0, 100, and 200 kg N ha-1) was conducted on a well-drained sandy loam of the Grenville series (coarse-loamy, mixed, mesic Typic Eutrochrepts) on the Central Experimental Farm at Ottawa, ON, in Canada (45 degrees 23' N, 75 degrees 43' W) for 3 yr (from 1991 to 1993) to evaluate whether canopy reflectance and greenness can measure changes in maize yield response to N fertility. Canopy reflectance, leaf area and greenness were measured on 11 dates from 4 wk before to 4 wk after anthesis. Grain yield at harvest was also measured. Direct radiometer readings at the 600- and 800-nm wavelengths or a derived normalized difference vegetation index [NDVI = (800 nm -600 nm)/(800 nm + 600 nm)] best differentiated N and hybrid treatments at most sampling dates. Canopy light reflectance was strongly correlated with field greenness at almost all growth stages (field greenness being a product of plant leaf area and leaf greenness measured with a chlorophyll meter, in this case a SPAD-502). Both canopy light reflectance and field greenness measured preanthesis were correlated with yield at harvest. Light reflectance measured after anthesis differentiated hybrid differences in leaf senescence. Our data suggest that light reflectance measurements prior to anthesis may predict grain yield response and provide in-season indications of N deficiency.

Mallawaarachchi, T., P. A. Walker, et al. (1996). "GIS-based integrated modelling systems for natural resource management." Agric syst 50(2): 169-189.
Natural resource management relies on the use of resource, economic and production data, which are often available at various non-comparable scales. This causes serious problems in data interpretation and on the availability and cross-compatibility of official data for detailed modelling and analysis. Integration of the spatial analytical capabilities of Geographic Information Systems and the constraint optimization power of mathematical programming facilitates the generation of composite data sets for extensive geographic regions. Integrated modelling offers the capacity to examine the effects of interacting properties of economic and natural systems. This paper presents an application of a modelling system for the assessment of land degradation costs in extensive areas of the state of New South Wales, Australia. It highlights the potential of the system to evaluate the feasibility of policy alternatives and program options at a broader regional level.

Mowrer, H. T., R. L. Czaplewski, et al. (1996). Spatial accuracy assessment in natural resources and environmental sciences : second international symposium. Fort Collins, Colo. (3825 East Mulberry St., Fort Collins 80524-8597), U.S. Dept. of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, [1996] viii, 728 p. : ill. (some col.), maps (some col.).

Penny, D. C., S. C. Nolan, et al. (1996). "Yield and nutrient mapping for site specific fertilizer management." Commun soil sci plant anal 27(5/8): 1265-1279.
Soil sampling using a 67 m X 67 m grid was carried out at four locations in conjunction with a precision (site-specific) farming study. The four locations were on undulating to rolling topography, distributed across the Brown, Dark Brown and Black soil zones of the plains region of western Canada. A Differential Global Positioning System (DGPS) was used for positioning to map yield, terrain, fertility, and salinity. These attribute maps were used to develop maps for variable rate fertilization. At each grid-line intersection (node), a composite sample consisting of 15 cores was taken within a 5 m radius. Sample depths were 0-15, 15-30, 30-60, and 60-90 cm. The nutrient levels within the areas sampled (15-25 ha) generally had a wide range, high standard deviation, and strong positive skewness. The large variations found in nutrient levels and crop yields support the need for variable rate fertilization. For conventional, constant rate fertilizer application, the strong positive skewness of nutrient levels obtained with grid sampling indicates that systematic errors occur with the current method of composite sampling of large fields. When grid sampling results have frequency distributions that are positively skewed, fertilizer recommendations based on composite sampling will under fertilize the majority of the field.

Perez Munoz, F. and T. S. Colvin (1996). "Continuous grain yield monitoring." Trans ASAE 39(3): 775-783.
Performance of an electronic yield monitor was evaluated in controlled and field environments. Laboratory experiments were conducted with forces applied by a universal testing machine on the grain flow sensor of the yield monitor. The yield monitor was then field tested on a combine on two different row lengths. The yield reported by the monitor in the laboratory was closely related to a calculated yield (r > 0.99). Yield results reported by the monitor in the field for the 100-m-long strips closely agreed with yields based on the amount of grain as determined by scales. When the monitor was used on 20-m rows there was more scatter in the results because of influence of starting and stopping delays as well as isolated pulses of grain out of the combine's grain elevator. The goal of splitting the signal-from a yield monitor on a continuously moving combine to provide spot yields within a field was not completely accomplished. Field results reported here and by users indicate that yield mapping with continuous flow monitors is feasible. These results further suggest that yield monitors are mechanically reliable and will provide accurate enough information for producer's yield maps.

Raines, G. L., D. L. Sawatzky, et al. (1996). Great Basin geoscience data base. [Reston, Va.?], U.S. Dept. of the Interior, U.S. Geological Survey ; Denver, CO : For sale by USGS Information Services, 1996. 2 computer laser optical discs.
Seventy-three digital GIS (Geographic Information Systems) data sets for the Great Basin presented in Federal Data Exchange, ESRI PC ARCVIEW1, and ESRI ARC/INFO formats. Covers Nevada, eastern California, southeastern Oregon, southern Idaho, and western Utah. Includes topographical, geochemical, geophysical, and thematic data sets.

Robert, P. C., R. S. Rust, et al. (1996). Proceedings of the Third International Conference on Precision Agriculture : June 23-26, 1996, Minneapolis, Minnesota. Madison, Wis., American Society of Agronomy : Crop Science Society of America : Soil Science Society of America, c1996. xxi, 1222 p. : ill.

Roderick, M., R. Smith, et al. (1996). "Calibrating long-term AVHRR-derived NDVI imagery." Remote sens environ 58(1): 1-12.

Roderick, M., R. Smith, et al. (1996). "The precision of the NDVI derived from AVHRR observations." Remote sens environ 56(1): 57-65.

Rogowski, A. S. (1996). "GIS modeling of recharge on a watershed." J environ qual 25(3): 463-474.
The study describes a model developed to delineate primary recharge contributing areas on a large watershed based on the field-measured parameters. The procedure uses measured values of soil water content, bulk density, hydraulic conductivity, and depth to water at 31 locations, to generate kriged overlays of input in a Geographic Information Systems (GIS) framework. The number of locations was a compromise between sampling efficiency and requirements of the geostatistical analysis. Mathematical operations on the overlays are carried out on a pixel-by-pixel basis to predict distributions of water flux from below the root zone, travel time to the groundwater, and recharge flux pulse at the water table. Comparison with field data suggests that flow may occur through only a portion of total pore space. Field application is illustrated on a 123 km2 catchment in Pennsylvania.

Singh, V. P. and M. Fiorentino (1996). Geographical information systems in hydrology. Boston, Kluwer Academic Publishers, 1996. xv, 443 p. : ill.

Smith, L. C. and M. Gluck (1996). Geographic information systems and libraries : patrons, maps, and spatial information : papers presented at the 1995 Clinic on Library Applications of Data Processing, April 10-12, 1995. [Urbana], Graduate School of Library and Information Science, University of Illinois at Urbana-Champaign, 1996. 240 p. : ill., maps.

Solie, J. B., W. R. Raun, et al. (1996). "Optical sensor based field element size and sensing strategy for nitrogen application." Trans ASAE 39(6): 1983-1992.
Fundamental field element sizes for the plant nitrogen spectral index (PNSI) were calculated for 12 transects at two locations in winter wheat. PNSI, the inverse of the NDVI, is a statistic calculated from the red and near-infrared radiance of wheat plants. Previously reported work had shown that PNSI was related to total N uptake, the amount of nitrogen in the vegetative portion of the plant. Based on semivariogram and mean difference analysis, the fundamental field element size for PNSI was shown to be between 0.70 and 4.6 m, with 1.4 m being the field element length common to all transects at two locations, one with nitrogen applied in the fall and one with no nitrogen applied in the fall. Semivariograms, for three transects, of PNSI averaged over 1.5 m long field elements and total N uptake determined by dry combustion from wheat harvested from the same field elements were similar in shape and supported the conclusion that the fundamental field element length should be in the range determined from PNSI analysis. Attempts to predict the total N uptake in a field element from measurements of PNSI in preceding field elements yielded errors greater than 9% compared to directly sensing PNSI in the field element. This research suggests that variable rate technology which treats field elements greater than 1.96 m2 will likely not optimize fertilizer N inputs while having the potential for misapplying fertilizers as a result of too coarse a grid.

Sonka, S. T. and K. F. Coaldrake (1996). "Cyberfarm: What does it look like? What does it mean." Am j agric econ 78(5): 1263-1268, 1281-1284.

Stone, M. L., J. B. Solie, et al. (1996). "Use of spectral radiance for correcting in-season fertilizer nitrogen deficiencies in winter wheat." Trans ASAE 39(5): 1623-1631.
Variable rate application technology based on spectral radiance has not previously been used for correcting in-season winter wheat nitrogen (N) deficiencies. Soil and yield mapping has been used to recommend variable amounts of applied fertilizer in crop production, however, both are restricted by the time required to obtain results and their utility is bound by the year in which they were generated. The objectives of this study were to determine the relationship between spectral radiance at specific wavelengths with wheat forage yield and forage N uptake, and to evaluate the potential use of spectral radiance measurements for correcting in-season wheat N deficiencies using sensor-based variable rate technology. Five studies were conducted, three in farmer fields where variable soil N deficiencies were present and two on Oklahoma Agricultural Experiment Station land. Spectral radiance readings for red and near-infrared (NIR) wavelengths were obtained in wheat between Feekes physiological stages 4 and 6 using photodiode-based sensors fitted with interference filters and interfaced to an embedded microcontroller. Correlation between a plant nitrogen spectral index (PNSI), a variation of the normalized-difference-vegetative-index (NDVI), and total N uptake in wheat forage was then established. Based on the PNSI readings, a variable 0 to 112 kg N ha-1 topdress N rate was determined for 3 X 3 m plots and N as urea ammonium-nitrate (UAN) applied accordingly (variable rate). In addition to the variable rate treatment, a fixed rate and a check plot (no N applied) were evaluated in a randomized complete block experiment. The PNSI was highly correlated with estimates of wheat forage N uptake at all.

Thurman, E. M. and M. T. Meyer (1996). "Herbicide metabolites in surface water and groundwater: introduction and overview."
Several future research topics for herbicide metabolites in surface and ground water are outlined in this chapter. They are herbicide usage, chemical analysis of metabolites, and fate and transport of metabolites in surface and ground water. These three ideas follow the themes in this book, which are the summary of a symposium of the American Chemical Society on herbicide metabolites in surface and ground water. First, geographic information systems allow the spatial distribution of herbicide-use data to be combined with geochemical information on fate and transport of herbicides. Next these two types of information are useful in predicting the kinds of metabolites present and their probable distribution in surface and ground water. Finally, methods development efforts may be focused on these specific target analyses. This chapter discusses these three concepts and provides an introduction to this book on the analysis, chemistry, and fate and transport of herbicide metabolites in surface and ground water.

Tim, U. S. (1996). "Emerging technologies for hydrologic and water quality modeling research." Trans ASAE 39(2): 465-476.
During the past two decades there has been a dramatic increase in the development and application of hydrologic and water quality models to evaluate complex environmental processes and to assess nonpoint source pollution of soil and water resources. Recognizing that advancements in modeling continue to be driven by developments in computer technology, it is worthwhile to examine some of the current and emerging computer technologies that hold great promise for advancing the use of hydrologic and water quality models. An attempt is made to forecast and briefly discuss the impact that technologies such as geographic information systems, global positioning systems, and scientific visualization will have on the future of hydrologic and water quality modeling. Forecasting is a very risky business, not because of our chronic inability to predict what will happen in the future but also because such speculation raises questions about what we modelers and model users desire and value. The thesis of this article is that some current and most of the emerging technologies will facilitate development and widespread use of hydrologic and water quality models for water resources management and decision making in the future.

Vanden Heuvel, R. M. (1996). "The promise of precision agriculture." J soil water conserv 51(1): 38-40.

Veroustraete, F., J. Patyn, et al. (1996). "Estimating net ecosystem exchange of carbon using the normalized difference vegetation index and an ecosystem model." Remote sens environ 58(1): 115-130.

Vetter, A. A. (1996). "Quantitative evaluation of DGPS guidance for aerial agricultural applications." Appl eng agric 12(5): 611-616.
The Global Positioning System (GPS) satellites provide positioning information which can be of significant use to agricultural aviation applicators. This article presents the results of a quantitative evaluation of the precision of agricultural aviation aircraft to be guided along swaths with a commercial device which incorporates differentially corrected GPS signals (DGPS) for position information. The precision of the cross-track displacement along the swath is determined with a video camera verification system and the results have been analyzed statistically. The data are analyzed to determine the precision of the DGPS position, pilot performance, and the total system performance. The quantitative tests have shown excellent cross-track precision. Under less than ideal conditions, the pilot maintained the aircraft within 0.33 m of the swath centerline 50% of the time and within 0.93 m for 90% of the time. The standard deviation of the aircraft from the centerline was 0.38 m.

Wagenet, R. J. and J. L. Hutson (1996). "Scale-dependency of solute transport modeling/GIS applications." J environ qual 25(3): 499-510.
The movement of water through the soil profile and the consequent displacement and transformation of chemicals dissolved in the water is a key concern in preventing water quality degradation, with its eventual impact on living systems, both human and otherwise. Predictions of the effect of a particular water and chemical management system at the soil surface will lead to more enlightened control of chemicals introduced into the environment as pesticides, fertilizers, or waste products. The use of geographic information systems (GIS) in concert with simulation modeling of soil leaching processes is becoming more widespread as a procedure applied to environmental chemical fate issues. The use of GIS has brought to the forefront the spatial scale of such databases as soil survey, elevation, climate and land use, and their use in the modeling process. An accompanying concern is the spatial scale at which any simulation model is assumed to be accurate, and the spatial scale at which both model input and field-verification data should be generated. Such modeling presently consists of a number of approaches, some useful at several spatial scales, and others more limited by the assumptions inherent in their development. This paper discusses these issues, and presents two case studies as examples.

Weisz, R., S. Fleischer, et al. (1996). "Site-specific integrated pest management for high-value crops: impact on potato pest management." J econ entomol 89(2): 501-509.
Site-specific agriculture optimizes agricultural inputs by varying application rates to match within-field requirements. Two years of trials were conducted in rotated commercial potato fields to compare traditional whole-field integrated pest management with site-specific management for Colorado potato beetle, Leptinotarsa decemlineata (Say), green peach aphid, Myzus persicae (Sulzer), and potato leafhopper, Empoasca fabae (Harris). Additionally, the spatial dynamics of Colorado potato beetle populations subjected to whole-field integrated pest management were studied. Colorado potato beetle infestations mostly remained near field edges throughout the season. Highest densities for each life stage remained near the locations of the initial colonizing adults. Even if management thresholds were as low as the 3rd density decile, between 60 and 95% of the field area could be left untreated when the mean density exceeded the threshold. Site-specific management reduced insecticide inputs for the green peach aphid but not for potato leafhopper. Initial Colorado potato beetle colonization pressure, measured as egg mass density approximately 7 d after crop emergence, was a significant covariable in determining season-long insecticide requirements. Analysis of covariance demonstrated that after accounting for this variable, site-specific management significantly reduced insecticide inputs compared with whole-field integrated pest management. Cumulative season-long Colorado potato beetle insecticide savings of 30-40% across a broad range of colonization pressures were observed.

Wilkins, D. E. (1996). "Tillage, seeding and fertilizer application technologies." Am J altern agric 11(2/3): 83-88.
Tillage, seeding and fertilizing implements for rainfed cereal production with a winter precipitation pattern have unique functional requirements. In designing and developing implements for these systems, soil and water conservation principles are critical and must be integrated into the total production system. Plant diseases, insects, weeds, environmental degradation, crop yield, crop quality and economics all may be influenced by tillage, seeding and fertilizing implements. Advances have been made in implements for improved residue management, stand establishment and crop fertilization that leave more crop residue on the surface for soil and water conservation. However, they alter the seed and root zones, often resulting in uncontrolled pests, reduced yields, or increased production costs. Research is needed to integrate production implements into ecosystem management through automatic control systems for improved tillage, seeding and fertilizing. These systems should include field history mapping, real-time soil sensors, and models to link data bases with equipment functions.

(1997). Precision agriculture in the 21st century : geospatial and information technologies in crop management. Washington, D.C., National Academy Press, 1997. ix, 122 p. : ill.

Acock, B. and Y. Pachepsky (1997). "Holes in precision farming: mechanistic crop models."

Akkal, N., M. H. Jeuffroy, et al. (1997). "Assessment of a method for estimating the nitrogen requirements of a wheat crop based on an early estimate of cover fraction."

Algerbo, P. A. and L. Thylen (1997). "Coast Guard Beacon System."

Audsley, E., B. J. Bailey, et al. (1997). "Decision support systems for arable crops: increasing precision in determining inputs for crop production."

Balsari, P. and M. Tamagnone (1997). "An automatic spray control for airblast sprayers: first results."

Balsari, P., M. Tamagnone, et al. (1997). "Directional control of agricultural vehicles."

Baumgartner, M. F., G. A. Schultz, et al. (1997). Remote sensing and geographic information systems for design and operation of water resources systems. Wallingford, Oxfordshire, UK, International Association of Hydrological Sciences, 1997. viii, 259 p. : ill., maps.

Bausch, W. C., H. R. Duke, et al. (1997). "Assessing and mapping the plant nitrogen status in irrigated corn."

Bergeijk, J. v., D. Goense, et al. (1997). "Dynamic weighing for accurate fertilizer application."

Biller, R. H., A. Hollstein, et al. (1997). "Precision application of herbicides by use of optoelectronic sensors."

Birrell, S. J. and J. W. Hummel (1997). "Multi-sensor ISFET system for soil analysis."

Blackmore, B. S. and G. Larscheid (1997). "Strategies for managing variability."

Booltink, H. W. G. and J. Verhagen (1997). "Integration of remote sensing, modeling and field measurements towards an operational decision support system for precision agriculture."

Bottinger, S. (1997). "Technical realization of a modularly built up information and communication system for agriculture."

Bouma, J. (1997). "From soil survey to a soil database for precision agriculture."

Buchleiter, G. W., W. C. Bausch, et al. (1997). "Multidisciplinary approach for precision farming research."

Buciene, A. and A. Svedas (1997). "Spatial variability of soil agrochemical properties and crop yield in Lithuania."

Carlson, T. N. and D. A. Ripley (1997). "On the relation between NDVI, fractional vegetation cover, and leaf area index." Remote sens environ 62(3): 241-252.

Casady, W. W. and D. L. Pfost (1997). "Farmer-dealer relationships in precision agriculture."

Christensen, S., T. Heisel, et al. (1997). "Spatial variation of pesticide doses adjusted to varying canopy density in cereals."

Colvin, T. S., D. L. Karlen, et al. (1997). "Comparisons of grain yield monitors to scales for mapping."

Colvin, T. S., D. B. Jaynes, et al. (1997). "Yield variability within a central Iowa field." Trans ASAE 40(4): 883-889.
Technologies to support precision farming (PF) began to emerge in 1989 when the Global Positioning System (GPS) became available to a limited extent and was tested as a means for locating farm equipment within fields. Substantial PF technology is available with rapidly decreasing costs and increasing capabilities. However, one major class of information that is missing is a method for determining how much material to apply or what action to take as a result of a specific condition at any position within a field. Developing this information will require knowing the spatial and temporal variability of plant response and will most likely be obtained by measuring yield variability. This field study was designed to quantify yield variability within a 16 ha field which has had consistent practices for several years. Crop yields showed a coefficient of variation ranging from near 12% in 1989 and 1992 to over 30% in 1990 and 1993. Rankings of the long-term relative yield for 224 locations were not stable even after 6 years when recalculated each year. Many PF scenarios are based on the assumption of a stable yield pattern within a field, but only a few points in this field have exhibited such a pattern. Perhaps stable patterns will eventually emerge, but the time frame for this to occur may be quite long. Overall, this study suggests that implementation of PF practices within the Clarion-Nicollet-Webster soil association area will reveal both difficulties and opportunities.

Costopoulou, C. I. and M. E. Anagnostou (1997). "Rural area networks for precision agriculture."

Curless, J. K. (1997). Interactions between soil chloride, pH and propanil applications on rice and utilizing global positioning systems in agriculture. 1997. x, 104 leaves, ill. (some col.), maps.

Daberkow, S. G. (1997). "Adoption rates for recommended crop management practices: implications for precision farming."

Daberkow, S., R. Heimlich, et al. (1997). "Estimating cost savings to agriculture from publicly available differential global positioning system." Mod agric 1(4): 28-29.

Dampney, P. M. R. and G. Goodlass (1997). "Quantifying the variability of soil and plant nitrogen dynamics within arable fields growing combinable crops."

Dampney, P. M. R., M. A. Froment, et al. (1997). "The variability of pH and available phosphorus, potassium and magnesium in soils within arable fields in England."

Dawson, C. J. and A. E. Johnston (1997). "Aspects of soil fertility in the interpretation of yield maps as an aid to precision farming."

Dawson, C. J. (1997). "Management for spatial variability."

Dingemans, M. J. (1997). "The practical implementation of precision farming for European agriculture."

Domsch, H. and O. Wendroth (1997). "On-site diagnosis of soil structure for site specific management."

Duke, H. R., G. W. Buchleiter, et al. (1997). "Site specific management of water and chemicals using self-propelled sprinkler irrigation systems."

Ehlert, D. and P. Jurschik (1997). "Techniques for determining heterogeneity for precision agriculture."

Ellis, R. H. (1997). "Determining appropriate seed sow rates."

Ellsbury, M. M., W. D. Woodson, et al. (1997). "Spatial characterization of adult emergence patterns and oviposition for corn rootworm populations in continuous and rotated corn."

Emmott, A., J. Hall, et al. (1997). "The potential for precision farming in plantation agriculture."

Engel, T. (1997). "Use of nitrogen simulation models for site-specific nitrogen fertilization."

Engqvist, A., P. Bengtsson, et al. (1997). "A model for site specific broad-leaved weed control based on weed plant variables."

Evans, E. J., R. S. Shiel, et al. (1997). "Optimisation of lime application to take account of within-field variation in pH and soil texture."

Everitt, J. H., J. V. Richerson, et al. (1997). "Detecting and mapping western pine beetle infestations with airborne videography, global positioning system and geographic information system technologies." Southwest entomol 22(3): 293-300.

Eversull, E. E. (1997). "A fertile trend: local co-ops embracing low-impact fertilizer technology." Rural coop 64(3): 17-19.

Fekete, A. and P. S. Lammers (1997). "Analysis of location error."

Ferguson, R. B., G. W. Hergert, et al. (1997). "Strategies for site-specific nitrogen management."

Fotyma, M., A. Faber, et al. (1997). "Preliminary experience concerning precision agriculture in Poland."

Francis, D. D. and J. S. Schepers (1997). "Selective soil sampling for site-specific nutrient management."

Gosche, J. M. (1997). "Ag retailers make the switch to site-specific farming." Mod agric 1(5): 24-26.

Green, H. M., W. K. Vencill, et al. (1997). "Precision management of spatially variable weeds."

Grenzdorffer, G. (1997). "Remote sensing and GIS for a site-specific farm management system."

Gupta, R. K., S. Mostaghimi, et al. (1997). "Spatial variability and sampling strategies for NO3-N, P, and K determinations for site-specific farming." Trans ASAE 40(2): 337-343.
NO3-N, P, and K nutrients data were analyzed to examine the extent of spatial variations in their concentration levels and to develop sampling strategies to obtain their representative mean concentrations and correlated characteristics in spatial domain. The study was conducted at two farms located within the Coastal Plains of Virginia. The nutrients' concentration values varied with coefficients of variation ranging from 13% to 40% at the two sites. Spatial variations along and across the rows at study site were the same at Brandon farm, but were different at the Renwood farm. The sample size required to determine the representative mean values of NO3-N and K nutrients could be decreased by about 40% to 60% if the associated error in the mean values was increased from 5% to 10% level. The concentration values of three nutrients exhibited spatially correlated dependence on their adjacent measurements. The correlation structures of nutrients could best be described by the exponential forms of the semi-variogram model for each site, except for K at Brandon site for which a spherical model was found to be more appropriate. Based on the spatial variability and correlation length of nutrients, sampling grids of 32 x 32 m size for NO3-N, P, and K determinations at the Brandon site, and of 18 x 32 m for NO3-N, 29 x 59 m for P, and 23 x 44 m for K determinations at the Renwood site are recommended. However, due to cost and practical considerations, sampling grid of 18 x 32 m size for the three nutrients is suggested for the Renwood site. A reduction of 12% in P fertilizer at Brandon and of 25% in K fertilizer at Renwood site could be achieved if fertilizer is applied at a variable rate based.

Hague, T., J. A. Marchant, et al. (1997). "A system for plant scale husbandry."

Han, S., S. M. Schneider, et al. (1997). "A bitmap method for determining effective combine cut width in yield mapping." Trans ASAE 40(2): 485-490.
In harvesting narrow row or broadcast crops such as wheat, the actual combine cut width can vary, significantly within a field. Assuming a constant combine cut width in the whole field to calculate crap yields will give incorrect results. In this study, a bitmap method is developed to determine the effective combine cut width from Global Positioning System (GPS) positions of the combine in the field. The method consists of first initializing a bitmap that represents the pre-harvest crop conditions in the field, and then progressively updating the bitmap to represent the up-to-date crop conditions during the harvest process. The effective combine cut width at each time step is derived by manipulating the changes of the bitmap during that time period. An example application of the method is shown with yield data for 1994 spring wheat. The average cut widths among combine passes varied from 1.18 m to 2.24 m, compared with a desired cut width of 1.52 m. The accuracy of the resulting yield maps was greatly improved by the bitmap method.

Haneklaus, S., I. Ruehling, et al. (1997). "Studies on the variability of soil and crop fertility parameters and yields in different landscapes of northern Germany."

Harris, D. (1997). "Risk management in precision farming."

Heermann, D. F., G. W. Buchleiter, et al. (1997). "Nondifferential GPS for use on moving irrigation systems."

Heisel, T., S. Christensen, et al. (1997). "Validation of weed patch spraying in spring barley--preliminary trial."

Hellebrand, H. J. and H. Beuche (1997). "Multicomponent positioning for site-specific farming."

Hergert, G. W., W. L. Pan, et al. (1997). "The adequacy of current fertilizer recommendations for site specific management in the USA."

Hergert, G. W. and R. B. Ferguson (1997). "The impact of variable rate N application on N use efficiency of furrows irrigated maize."

Huemmrich, K. R. and S. N. Goward (1997). "Vegetation canopy PAR absorptance and NDVI: an assessment for ten tree species with the SAIL model." Remote sens environ 61(2): 254-269.

Huete, A. R., H. Q. Liu, et al. (1997). "A comparison of vegetation indices over a global set of TM images for EOS-MODIS." Remote sens environ 59(3): 440-451.

Jurschik, P. (1997). "Information management for precision farming."

Karlen, D. L., C. A. Cambardella, et al. (1997). "Spatial and seasonal factors affecting crop yield and N removal from glacial till soils."

Koeijer, T. J. d., G. J. M. Oomen, et al. (1997). "Environmental and economic effects of site specific and weather adapted nitrogen fertilization for a Dutch field crop rotation."

Kristensen, K. and S. E. Olesen (1997). "Mapping root zone capacity by co-kriging aerial photographs and point measurements of available soil moisture."

Lake, J. V., G. Bock, et al. (1997). Precision agriculture : spatial and temporal variability of environmental quality. Chichester ; New York, Wiley, 1997. viii, 251 p. : ill.

Lamb, J. A., R. H. Dowdy, et al. (1997). "Spatial and temporal stability of corn grain yields." J prod agric 10(3): 410-414.
Year-to-year consistency of crop yields within a farm field is needed to use grain yield monitor data for site-specific management decisions such as yield goals for fertilizer recommendations. A 5-yr study was conducted from 1991 to 1995 to determine whether patterns of corn (Zea mays L.) grain yields are similar over a number of years and whether grain yields from one or more years can be used to predict grain yields for subsequent years. The experimental site was located at the Northern Cornbelt Sand Plain Management Systems Evaluation Area near Princeton, MN. The research area was 4.4 acres with soils mapped as three variants of the Zimmerman fine sand (mixed, frigid, argic, Udipsamment) and a Cantlin loamy fine sand (sandy, mixed, frigid, typic, Udipsamment). Continuous corn was grown from 1990 through 1995 after alfalfa (Medicago sativa L.) from 1981 through 1989. Cultural practices were applied uniformly to the 4.4 acre site each year. The 4.4 acres were divided into 60 grid cells (50 ft. by 60 ft.) and grain yields, corrected to 15.5% moisture, were determined by hand harvesting an area (two rows 20 ft. long) within each of the 60 grid cells. Differences between highest and lowest continuous corn grain yields in the research area were 72 bu/acre in 1991, 44 bu/acre in 1992, 45 bu/acre in 1993, 51 bu/acre in 1994, and 57 bu/acre in 1995. Grain yields were not spatially consistent from year to year. Areas with better grain yields were not consistent from year to year, and conversely, poor production areas were not fused in similar locations each year. Only 4 to 42% of the grain yield variability for a given year is accounted for by a knowledge of the grain yields from a previous year. The.

Lark, R. M., J. V. Stafford, et al. (1997). "Exploratory analysis of yield maps of combinable crops."

Lark, R. M. (1997). "Variation in soil conditions and crop performance."

Larscheid, G., B. S. Blackmore, et al. (1997). "Management decisions based on yield maps."

Le Bars, J. M., D. Boffety, et al. (1997). "Location improvement by combining a D-GPS system with on-field vehicle sensors."

Leake, A. R. and G. A. Paulson (1997). "An evaluation of soil mineral N, leaf chlorophyll status and crop canopy density on the yield of winter wheat."

Leiva, F. R., J. Morris, et al. (1997). "Precision farming techniques for sustainable agriculture."

Liao, H. H. and U. S. Tim (1997). "An interactive modeling environment for non-point source pollution control." J Am Water Resour Assoc 33(3): 591-603.
Non-point source pollution continues to be an important environmental and water quality management problem. For the most part, analysis of non-point source pollution in watersheds has depended on the use of distributed models to identify potential problem areas and to assess the effectiveness of alternative management practices. To effectively use these models for watershed water quality management, users depend on integrated geographic information systems (GIS)-based interfaces for input/output data management. However, existing interfaces are ad-hoc and the utility of GIS is limited to organization of input data and display of output data. A highly interactive water quality modeling interface that utilizes the functional components and analytical capability of GIS is highly desirable. This paper describes the tight coupling of the Agricultural Non-point Source (AGNPS) water quality model and ARC/INFO GIS software to provide an interactive hybrid modeling environment for evaluation of non-point source pollution in a watershed. The modeling environment is designed to generate AGNPS input parameters from user-specified GIS coverages, create AGNPS input data files, control AGNPS model simulations, and extract and organize AGNPS model output data for display. An example application involving the estimation of pesticide loading in a southern Iowa agricultural watershed demonstrates the capability of the modeling environment. Compared with traditional methods of watershed water quality modeling using the AGNPS model or other ad-hoc interfaces between a distributed model and GIS, the interactive modeling environment system is efficient and significantly reduces the task of watershed analysis using tightly.

Long, R. C., H. Seltmann, et al. (1997). "Precision application of agricultural chemicals."

Lord, E. I., M. A. Shepherd, et al. (1997). "Yield variation and crop water use: Cause or effect."

Lu, Y. C. and B. Watkins (1997). "Economic and environmental evaluation of variable rate nitrogen fertilizer applications using a biophysical model."

Lu, Y. C., C. Daughtry, et al. (1997). "The current state of precision farming." Food rev int 13(2): 141-162.

Lutticken, R. (1997). "Mapping and managing spatial nutrient variability on different field scales in Germany--a system approach from a service provider's viewpoint."

Lutticken, R., W. Koch, et al. (1997). "The potential of yield maps and soil survey data in low cost site specific farming strategies."

Mack, G. (1997). "Precise positioning for agriculture."

Matthews, R. and S. Blackmore (1997). "Using crop simulation models to determine optimum management practices in precision agriculture."

Mazzetto, F., S. Landonio, et al. (1997). "Farm activity information system based on automatic detection of machinery use."

McBratney, A. B. and M. J. Pringle (1997). "Spatial variability in soil-implications for precision agriculture."

McKinion, J. M., R. L. Olson, et al. (1997). "Model-based decision support systems for precision agriculture in cotton production."

Miller, P. C. H. and J. H. Combellack (1997). "The performance of an air/liquid nozzle system suitable for applying herbicides in a spatially selective manner."

Missotten, B., G. Strubbe, et al. (1997). "Straw yield mapping: a tool for interpretation of grain yield differences within a field."

Missotten, B., B. Broos, et al. (1997). "A yield sensor for forage harvesters."

Mizgalewicz, P. J. and D. R. Maidment (1997). Modeling agrichemical transport in midwest rivers using geographic information systems. [Austin, Tex.], Center for Research in Water Resources, University of Texas at Austin, c1997.

Mowrer, H. T. (1997). Decision support systems for ecosystem management : an evaluation of existing systems. Fort Collins, Colo., U.S. Dept. of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, [1997] iv, 154 p.

Mulla, D. J. and A. U. Bhatti (1997). "An evaluation of indicator properties affecting spatial patterns in N and P requirements for winter wheat yield."

Nordmeyer, H., A. Hausler, et al. (1997). "Patchy weed control as an approach in precision farming."

Olieslagers, R., H. Ramon, et al. (1997). "Performance of a continuously controlled spinning disc spreader for precision application of fertilizer."

Oliver, M. A., Z. Frogbrook, et al. (1997). "A rational strategy for determining the number of cores for bulked sampling of soil."

Ostergaard, H. S. (1997). "Agronomic consequences of variable N fertilization."

Pachepsky, T. and B. Acock (1997). "Holes in precision farming: spatial variability of essential soil properties."

Paice, M. E. R. and W. Day (1997). "Using computer simulation to compare patch spraying strategies."

Parker, W. E., S. T. D. Turner, et al. (1997). "Developing a GIS-based tool for testing field sampling plans by modelling the within-field distribution of Brevicoryne brassicae in brussels sprouts."

Paruelo, J. M., H. E. Epstein, et al. (1997). "ANPP estimates from NDVI for the central grassland region of the United States." Ecology 78(3): 953-958.

Paz, S. M., C. E. Cugnasca, et al. (1997). "Development of a simulation tool for a GPS receiver."

Penuelas, J., R. Isla, et al. (1997). "Visible and near-infrared reflectance assessment of salinity effects on barley." Crop sci 37(1): 198-202.
We studied the effects of a soil salinity gradient (0.8-1.9 dS m-1 ECa) on spectral reflectance of 10 genotypes of barley (Hordeum vulgare L.) to determine the efficacy of reflectance as a tool for assessing the responses of barley to salinity. NDVI [normalized difference vegetation index, (R900 nm - R680 nm)/(R900 nm + R680 nm)] and WI (water index, R970 nm/R900 nm) were the reflectance indices used. In response to increasing salinity, near infrared reflectance decreased and visible reflectance increased, thereby lowering NDVI from 0.85 to 0.4, in parallel with decreases in biomass (from 2500-500 g m-2) and yield (from 900-50 g m-2). NDVI was, thus, a good indicator of biomass and yield. WI increased from 0.73 to 0.96, (canopy temperature minus air temperature) increased from -2 to 7 degrees C, and 13C discrimination in mature kernels decreased from 19 to 14.5 with increasing salinity levels. WI was, thus, related to crop water status response to salinity. NDVI and WI were, therefore, useful for measuring agronomic responses of barley to salinity.

Persson, K. and L. Moller (1997). "Development and implementation of site specific fertilization in Denmark, methods and results."

Petrzelka, P., S. Padgitt, et al. (1997). "Teaching old dogs survival tricks: a case study in promoting integrated crop management." J prod agric 10(4): 596-602.
New technology in crop production is emerging that can provide site-specific field and crop detail information to some operators. Satellite positioning, commonly referred to as global positioning systems, mapping software, and yield-monitoring equipment are all high-tech methods of providing this precision agriculture. But precision agriculture, or at least long strides in that direction, is possible short of these methods and capital investments. Integrated Crop Management (ICM) is one alternative to providing information-intensive management and precision farming, without the need for hard technology. Major elements of an ICM program include thorough crop production and protection planning, crop rotations, tillage management, and nutrient testing, as well as varying fertility rates based on manure and legume credits, scouting for weeds/insects/diseases, and keeping and analyzing field based records. Inherent in ICM is the involvement of the producer in increasing management tools and the knowledge base to make a decision. This knowledge base is generated to a significant degree from on-farm or site-specific observations. The Iowa Model Farms Demonstration Project (IMFDP) was an extension service program established to encourage farmers to adopt ICM practices. Evaluation of the program reveals that opportunities existed for refined practices among the sample of cooperators, although this was not recognized by all, as nearly half of the original participants did not complete the 3-yr project. Among those who remained in the project, several practices were refined and resulted in increased profitability. Among participants who discontinued the program, many perceived.

Putten, A. H. J. v. d. and M. J. D. Hack ten Broeke (1997). "Exploration of a technique to exclude fertilizer from urine patches in grazed pastures."

Quattrochi, D. A. and M. F. Goodchild (1997). Scale in remote sensing and GIS. Boca Raton, Fla., Lewis Publishers, c1997. 406 p. : ill.

Sadler, E. J., C. R. Camp, et al. (1997). "A site-specific irrigation system for the southeastern USA Coastal Plain."

Saraiva, A. M., S. M. Paz, et al. (1997). "Improving a planter monitor with a GPS receiver."

Scarlett, A. J., J. C. Lowe, et al. (1997). "Precision tillage: in-field, real-time control of seedbed quality."

Scarr, M. R., C. C. Taylor, et al. (1997). "Automatic recognition of weeds and crops."

Schmerler, J. and P. Jurschik (1997). "Technological and economic results of precision farming from a 7,200 hectares farm in East Germany."

Schneider, S. M., R. A. Boydston, et al. (1997). "Mapping of potato yield and quality."

Schroder, D., S. Haneklaus, et al. (1997). "Information management in precision agriculture with LORIS."

Schueller, J. K. (1997). "Technology for precision agriculture."

Schutz, Y. and A. Chambaz (1997). "Could a satellite-based navigation system (GPS) be used to assess the physical activity of individuals on earth." Eur j clin nutr 51(5): 338-339.
Objectives: To test whether the Global Positioning System (GPS) could be potentially useful to assess the velocity of walking and running in humans. Subject: A young man was equipped with a GPS receptor while walking running and cycling at various velocity on an athletic track. The speed of displacement assessed by GPS, was compared to that directly measured by chronometry (76 tests). Results: In walking and running conditions (from 2-20 km/h) as well as cycling conditions (from 20-40 km/h), there was a significant relationship between the speed assessed by GPS and that actually measured (r = 0.99, P < 0.0001) with little bias in the prediction of velocity. The overall error of prediction (s.d. of difference) averaged +/- 0.8 km/h. Conclusion: The GPS technique appears very promising for speed assessment although the relative accuracy at walking speed is still insufficient for research purposes. It may be improved by using differential GPS measurement.

Sheng, T. C., R. E. Barrett, et al. (1997). "Using geographic information systems for watershed classification and rating in developing countries." J soil water conserv 52(2): 84-89.

Shiel, R. S., S. B. Mohamed, et al. (1997). "Planning phosphorus and potassium fertilisation of fields wih varying nutrient content and yield potential."

Simmelsgaard, S. E. and J. Djurhuus (1997). "The possibilities of precision fertilization with N, P and K based on plant and soil parameters."

Snyder, C. (1997). "Economics of site-specific farming methods." Mod agric 1(1): 35.

Stafford, J. V., B. Ambler, et al. (1997). "Cut width sensors to improve the accuracy of yield mapping systems."

Stafford, J. V. and J. V. Benlloch (1997). "Machine-assisted detection of weeds and weed patches."

Stafford, J. V. (1997). Precision agriculture '97 : papers presented at the first European Conference on Precision Agriculture, Warwick University Conference Centre, UK, 7-10 September 1997. Oxford ; Herndon, VA, BIOS Scientific Pub., c1997. 2 v. (xiv, 997 p.) : ill.

Stein, A., J. Brouwer, et al. (1997). "Methods for comparing spatial variability patterns of millet yield and soil data." Soil Sci Soc Am j 61(3): 861-870.
This paper investigates methods to compare spatial patterns of pearl millet [Pennisetum glaucum (L.) R. Br.] yield with spatial patterns of soil variables in a farmer's 1-ha field on an undulating sand plain in Niger near ICRISAT-SC. Spatial pattern comparisons are important for precision farming applications. Methods included the correlation coefficient, linear regression, a distance measure to compare separate maps and the cross-correlation function. Millet grain yield varied from 0 to 2885 kg ha-1 on 5 by 5 m sub-plots. Pearl millet yield was correlated with measured soil variables at three different depths, elevation, and crust formation for two successive years. Only 30% of the total variation in millet dry yield was explained by regressing yield against soil variables. Detrended elevation showed a significant negative relation with yield (r = -0.421). The cation-exchange capacity (CEC) at all the depths showed a significant negative relation with yield (r of -0.238 to -0.290) because crusting and erosion increase with CEC extending to distances up to 30 to 40 m. Pattern comparison using the cross-correlogram related local hillocks in the area with high yields and local dips with low yields at a distance of 15 to 20 m. From this study, we concluded that the cross-correlogram was beneficial to compare data at various distances. Yield patterns are best explained by soil variables related to erosion as the major determining factor in the area.

Steven, M. D. and C. Millar (1997). "Satellite monitoring for precision farm decision support."

Stevens, G., S. Hefner, et al. (1997). "Variable rate lime application with global positioning system." Proc Beltwide Cotton Conf 1: 603-605.

Sudduth, K. A. (1997). "Spatial modeling of crop yield using soil and topographic data."

Swindell, J. E. G. (1997). "Mapping the spatial variability in the yield potential of arable land through GIS analysis of sequential yield maps."

Taylor, J. C., G. A. Wood, et al. (1997). "Mapping yield potential with remote sensing."

Taylor, J. C., G. Thomas, et al. (1997). "Diagnosing sources of within-field variation with remote sensing."

Thomsen, A., K. Schelde, et al. (1997). "Mapping of field variability in crop development and water balance within a field with highly variable soil conditions."

Thylen, L., P. Jurschik, et al. (1997). "Improving the quality of yield data."

Thylen, L. (1997). "Consistency in yield variation and optimal nitrogen rate."

Tieszen, L. L., B. C. Reed, et al. (1997). "NDVI, C3 AND C4 production, and distributions in Great Plains grassland land cover classes." Ecol appl 7(1): 59-78.

Traynor, J. M. (1997). Watershed assessment model : final project report. [Edmonton], Alberta Environmental Protection, [1997] vii, 20, [37] p. : ill., maps.

Turner, C., III (1997). "G.P.S. controlled precision spraying minimizing costs and environmental impact." Proc Beltwide Cotton Conf 1: 70.

Verhagen, J. (1997). "Modeing soil and crop responses in a spatially variable field."

Vieri, M. and P. Spugnoli (1997). "A high pressure injection system for precision application of pesticide."

Viscarra Rossel, R. A. and A. B. McBratney (1997). "Preliminary experiments towards the evaluation of a suitable soil sensor for continuous, 'on-the-go' field pH measurements."

Vrindts, E. and J. d. Baerdemaeker (1997). "Optical discrimination of crop, weed and soil for on-line weed detection."

Walter, A. M., T. Heisel, et al. (1997). "Shortcuts in weed mapping."

Webster, T. M. and J. Cardina (1997). "Accuracy of a global positioning system (GPS) for weed mapping." Weed technol 11(4): 782-786.

Weiss, M. D. (1997). "Phosphorus fertilizer application under precision farming: a simulation of economic and environmental implications."

Wendroth, O., G. Kuhn, et al. (1997). "State-space approach for site-specific management decisions."

Wheeler, P. N., R. J. Godwin, et al. (1997). "Trailer based yield mapping."

Whelan, B. M. and A. B. McBratney (1997). "Sorghum grain flow convolution within a conventional combine harvester."

White, J. G., R. M. Welch, et al. (1997). "Soil zinc map of the USA using geostatistics and geographic information systems." Soil Sci Soc Am j 61(1): 185-194.
The geographic distribution of soil Zn is important to agriculture, nutrition, and health. A map illustrating the total Zn content of soils of the conterminous USA was developed using geostatistics and geographic information systems. Data were combined from a U.S. Geological Survey study targeting nonagricultural soils in 47 states, and a U.S. Department of Agriculture-U.S. Environmental Protection Agency-U.S. Food and Drug Administration study targeting agricultural soils in 33 states. Semivariograms indicated spatial correlation at distances up to 470 km. A significant quadratic trend was modeled, but detrending had little effect on the semivariogram or on interpolation via kriging. The data exhibited some anisotropy, but it had little effect on kriging. An exponential semivariogram model was fit using least squares and used to krige a grid covering the conterminous USA. The resultant map depicted soils north of about 37 degrees N latitude or west of about 109 degrees W longitude as generally having more Zn than the average of 55 mg kg-1. Soils southeast of this boundary tended to contain less Zn than average, with exceptions of soils developed on Mississippi alluvium and in Piedmont valleys and ridges. High estimate standard deviations occurred where data were sparse. The map will be useful in future research to determine the geographic distribution of plant-available soil Zn, regional patterns of plant, animal, and human Zn deficiencies, the relationship of Zn to soil parent material, genesis, and surficial geology, and in considering the consequences of land disposal of Zn-laden wastes.

Wild, K., G. Rodel, et al. (1997). "GPS based soil sampling with an auger and field analysis of nitrate."

Wilson, J. D. (1997). "Precision agriculture: farming goes high tech." Mod agric 1(1): 21-23.

Wolf, S. A. and S. D. Wood (1997). "Precision farming: environmental legitimation, commodification of information, and industrial coordination." Rural sociol 62(2): 180-206.
Precision farming--use of digital geographically referenced data in farming operations--is the leading example of a cluster of emerging information technologies in agriculture. To date, the vast majority of academic and promotional literature addressing precision farming has focused on the field and farm-level economic and environmental benefits of site-specific allocation of crop inputs (fertilizer, pesticides, and seeds). In this paper, we question popular perceptions of the technology and pursue a sociological analysis through identification of consistencies between precision farming and the political and economic requirements of an industrializing agriculture. Through promotion of a public commitment and a technical mechanism to mitigate farm chemical pollution, precision farming legitimates chemically-based agriculture in an era of rising environmentalism. Further, precision farming is based on, and will advance, the commodification of agricultural information-appropriation of field and farm-level decision processes through substitution of capital for local knowledge. By automating farm-level data collection and information management and by reducing agriculturalists' reliance on public sector agricultural research and extension, precision farming supports further integration of on-farm activity into a coordinated system of industrial manufacture.

Yang, C., G. J. Shropshire, et al. (1997). "Measurement of ground slope and aspect using two inclinometers and GPS." Trans ASAE 40(6): 1769-1776.
Slope and aspect are two important topographic attributes affecting crop production. In order to quantitatively describe the influence of slope and aspect, two electronic inclinometers and a GPS (Global Positioning System) receiver were installed on two combines and a tractor to measure ground slope and aspect under actual field working conditions. A computerized data acquisition system was used to sample angle data and position information. The general case of a vehicle moving on ground having both direct and cross slopes was examined and algorithms were developed to calculate ground slope and aspect based on the angles measured by the inclinometers and the position data from GPS. Field tests showed the system performed well under severe conditions. A comparison between the calculated slope and aspect values and those derived from a contour map showed that the procedures and algorithms presented in this article were correct and accurate.

Zuydam, R. P. v., C. Werkhoven, et al. (1997). "High-accuracy remote position fix and guidance of moving implements in the open field: tests on sensor accuracy."

(1998). Proceedings of the First International Conference Geospatial Information in Agriculture and Forestry : decision support, technology, and applications : 1-3 June, 1998, Lake Buena Vista, Florida, USA. Ann Arbor, MI, ERIM International, c1998. 2 v. : ill. (some col.).

Al Gaadi, K. A. and P. D. Ayers (1998). "Assembling a real-time DGPS--testing and investigating factors that affect its accuracy." Appl eng agric 14(6): 659-665.
A real-time differentially corrected global positioning system (RDGPS) was assembled and tested in the field. The RDGPS was assembled using two GPS receivers and two radios. One receiver was utilized as a base station receiver and its antenna was fixed at a benchmark, while the other was used as a mobile receiver (rover). RDGPS accuracy was tested by collecting position data from the rover and comparing it to a previously determined position of a point in the field. The effect of imprecise position determination of base station benchmark on the RDGPS accuracy was investigated. Moreover, the effect of the age of differential correction messages on position determination accuracy produced by the rover was revealed. The RDGPS maintained an average accuracy of less than one meter. The average position determination error produced by the rover was almost equal to and in the opposite direction of the error in base station benchmark coordinates. Seventy-two percent of the tested rover data maintained an accuracy of less than 3 m with a correction message age of less than 29 s. However, location determination error of the rover reached up to 30.84 m with a correction message age of 98 s.

Beverly, R. B. and M. W. Van Iersel (1998). "Calibration of a video image analysis system for measurement of stem length, leaf area, and percent ground coverage." Commun soil sci plant anal 29(9/10): 1071-1081.
A relatively low-cost digital measurement system configured with off-the-shelf components (a standard consumer High 8-mm camcorder, video cassette recorder, video monitor, desktop computer with image capture board, and image analysis software) has been used in applications from benchtop stem length and leaf area measurements to aerial imaging for precision agriculture applications. However, preliminary research identified a systematic error in estimating leaf area using this system, which further investigation revealed to be caused by the internal calibration method used. Further research was needed to determine appropriate calibration methods for length and area measurements using this system. Length measurements were very accurate and repeatable using a vertical (i.e., parallel to the axis of objects) two-point calibration. Two-point (vertical, horizontal or diagonal) calibration led to over- or under-estimation of area, but three-point calibration yielded very accurate measurements of area and percent coverage. This system proved to be a versatile and useful method of measuring many plant size parameters.

Boone, M. Y. L., J. A. Landivar, et al. (1998). "Performance of ICEMM-cotton simulation model in a precision agriculture study." Proc Beltwide Cotton Conf 1: 428-430.

Bryceson, K. P. and E. Leonard (1998). Lost in space? : the abc of spatial information in rural land management. Glen Osmond, [S. Aust.], Cooperative Research Centre for Soil & Land Management, [1998] 24 p. : col. ill., col. maps.

Burgan, R. E. and C. H. Chase (1998). NDVI and derived image data : data archives 1997. Ogden, Utah, U.S. Dept. of Agriculture, Forest Service, Rocky Mountain Research Station, [1998?] 5 computer optical discs : col.

Clark, R. L. and R. Lee (1998). "Development of topographic maps for precision farming with kinematic GPS." Trans ASAE 41(4): 909-916.
The objective of this study was to examine the potential to use real-time kinematic differential GPS (RTK-DGPS) to collect GPS data on a moving vehicle for the development of topographic maps. An intensive study on a 1.5 ha field on an approximate 3 m grid spacing was first conducted, using two GPS data collection modes, stop & go (using a tripod GPS antenna mount) and kinematic (with tractor mounted GPS antenna). It was found that the standard deviation of the elevation error between 10 true error points and the calculated topographic surface ranged from 2 to 3 cm for data collected on an approximate 3 m grid. The elevation error for derived grid spacings of 9, 18, and 33 m ranged from 2 to 5 cm. On a second 20 ha field, only RTK-DGPS data was collected on an approximate 10 m grid spacing, with a resulting elevation error of 4 cm using stop-and-go true error points, and 6 cm using RTK-DGPS true error points. A third 115 ha field was studied by collecting data on an approximate 30 m grid with RTK-DGPS, with a resulting elevation error of 9 cm. The results are positive and indicate that the technique of collecting RTK-DGPS data on a moving vehicle is a viable means by which data can be collected to quickly develop topographic maps for precision farming and other applications.

Cook, S. E. and R. G. V. Bramley (1998). "Precision agriculture--opportunities, benefits and pitfalls of site-specific crop management in Australia." Aust j exp agric 38(7): 753-763.

Correia, F. N., F. C. Rego, et al. (1998). "Coupling GIS with hydrologic and hydraulic flood modelling." Water resour manag 12(3): 229-249.
Geographic Information Systems (GIS) have been recognised as a powerful means to integrate and analyse data from various sources in the context of comprehensive floodplain management. As part of this comprehensive approach to floodplain management, it is very important to be able to predict the consequences of different scenarios in terms of flooded areas and associated risk. Hydrologic and hydraulic modelling plays a crucial role and there is much to gain in incorporating these modelling capabilities in GIS. This is still a rather complex task and research is being done on the full integration of these models. Interfacing between these models and GIS may be a very efficient way of overcoming the difficulties and getting very good results in terms of engineering practice. This paper presents results based on the use of Intergraph GIS coupled with Idrisi GIS. Using these two systems substantially increased the flexibility of using GIS as a tool for flood studies. A lumped (XSRAIN) and a distributed (OMEGA) hydrologic models were used to simulate flood hydrographs. The well known HEC-2 Hydraulic model was used to compute flooded areas. These models were applied in the Livramento catchment with very good results. The computation of flooded areas for different flood scenarios, and its representation in GIS, can be used in the assessment of affected property and associated damages. This is a very useful GIS-based approach to floodplain management.

Cox, C. and C. Madramootoo (1998). "Application of geographic information systems in watershed management planning in St. Lucia." Comput electron agric 20(3): 229-250.

Daberkow, S. G. and W. D. McBride (1998). "Socioeconomic profiles of early adopters of precision agriculture technologies." J agribusiness 16(2): 151-168.

Dewees, S. and T. Collins (1998). "Geographic information systems: a tool for rural community research." South rural sociol 14: 1-17.
Because of their traditional application in the environmental and geological sciences, geographic information systems are not usually considered to be useful tools for rural community research or analysis. The 1990 census made socio-economic data available at the block-group level, however, and this has facilitated the mapping of socio-economic variables in small areas. Insight, explanation, and understanding can come from seeing data in their spatial context. Citizen researchers in the Jackson County, KY, Empowerment Zone used block-group level data in maps of their county to study socio-economic patterns in their communities. This paper provides an example of a way to use simple mapping techniques to illuminate social and economic patterns in small areas.

Dijksterhuis, H. L., L. G. v. Willigenburg, et al. (1998). "Centimetre-precision guidance of moving implements in the open field: a simulation based on GPS measurements." Comput electron agric 20(3): 185-197.

Doyle, D. (1998). Simulation models, GIS and nonpoint-source pollution (II) : January, 1994-October, 1994 : 176 citations from AGRICOLA. [Beltsville, Md.], Water Quality Information Center, National Agricultural Library, Agricultural Research Service, U.S. Dept. of Agriculture, [1998?].

Evans, M. D., C. N. Thai, et al. (1998). "Development of a spectral imaging system based on a liquid crystal tunable filter." Trans ASAE 41(6): 1845-1852.
This article presents an approach to the integration of a liquid crystal tunable filter into a monochrome video imaging system and provides a scheme for leveling the system response across wavelengths in the face of varying illumination, filter transmittance, camera lens aperture settings, and gain response. The scheme developed here uses the filter attenuation control and the camera gain control, both of which can be controlled via software. This system was applied to the evaluation of vigor of bush bean plants grown under different nitrogen treatments (from 30 to 120 ppm N). Using plant images captured at 695 nm and 760 nm, a Normalized Difference Vegetation Index (NDVI) was computed for each plant canopy and showed a increasing trend with increasing nitrogen treatments.

Frohn, R. C. (1998). Remote sensing for landscape ecology : new metric indicators for monitoring, modeling, and assessment of ecosystems. Boca Raton, Lewis Publishers, c1998. 99 p. : ill. (some col.), map.

Hanna, K. C. and R. B. Culpepper (1998). GIS in site design : new tools for design professionals. New York, Wiley, c1998. xvi, 223 p. : ill., maps 1 computer laser optical disc (4 3/4 in.).

Hassan, R. M. (1998). Maize technology development and transfer : a GIS application for research planning in Kenya. Oxon ; New York, Cab International in association with the International Maize and Wheat Improvement Centre and the Kenya Agricultural Research Institute, c1998. xxiv, 230 p. : ill., maps (some col.).

Heimlich, R. (1998). "Precision agriculture: information technology for improved resource use." Agric outlook(250): 19-23.

Heuvelink, G. B. M. (1998). Error propagation in environmental modelling with GIS. London ; Bristol, PA, Taylor & Francis, c1998. xviii, 127 p. : ill.

Joao, E. M. (1998). Causes and consequences of map generalisation. London ; Bristol, PA, Taylor & Francis, c1998. xv, 266 p. : ill., maps.

Johnston, C. A. (1998). Geographic information systems in ecology. Oxford ; Malden, MA, Blackwell Science, 1998. viii, 239 p. : ill., maps.

Kitron, U. (1998). "Landscape ecology and epidemiology of vector-borne diseases: tools for spatial analysis." J med entomol 35(4): 435-445.
Geographic information systems (GIS), global positioning systems (GPS), remote sensing, and spatial statistics are tools to analyze and integrate the spatial component in epidemiology of vector-borne disease into research, surveillance, and control programs based on a landscape ecology approach. Landscape ecology, which deals with the mosaic structure of landscapes and ecosystems, considers the spatial heterogeneity of biotic and abiotic components as the underlying mechanism which determines the structure of ecosystems. The methodologies of GIS, GPS, satellite imagery, and spatial statistics, and the landscape ecology-epidemiology approach are described, and applications of these methodologies to vector-borne diseases are reviewed. Collaborative studies by the author and colleagues on malaria in Israel and tsetse flies in Kenya, and Lyme disease, LaCrosse encephalitis, and eastern equine encephalitis in the north-central United States are presented as examples for application of these tools to research and disease surveillance. Relevance of spatial tools and landscape ecology to emerging infectious diseases and to studies of global change effects on vector-borne diseases are discussed.

Lang, L. (1998). Managing natural resources with GIS. Redlands, Calif., Environmental Systems Research Institute, c1998. ix, 117 p.: ill. (some col.), col. maps 1 computer laser optical disc (col., sd. ; 4 3/4 in.).

Lark, R. M. and J. V. Stafford (1998). "Information on within-field variability from sequences of yield maps: multivariate classification as a first step of interpretation." Nutr cycl agroecosyst 50(1/3): 277-281.

Lefko, S. A., L. P. Pedigo, et al. (1998). "Spatial modeling of preferred wireworm (Coleoptera: Elateridae) habitat." Environ entomol 27(2): 184-190.
Potential damage to crops after the Conservation Reserve Program is widespread. One probable result is the increased occurrence of soil-insect pests, primarily wireworms (Coleoptera: Elateridae). The likelihood of wireworm problems in the Iowa Conservation Reserve Program was compounded by the large amount of land enrolled in the program and the economic importance of corn, Zea mays L., the crop most often damaged by wireworms in the state. As a result, farmers need to consider pest management options that should include pest scouting. Wireworm presence/absence data from 1995 and 1996, and estimates of soil moisture from 89 Conservation Reserve Program fields were used to estimate variables useful for identifying where wireworms are more likely to occur. The most useful variables were a soil-moisture threshold of 17% and a moisture analysis that included meteorological data from only 1 yr before sampling occurred. These variables were coupled with a hydrologic model and embedded in a geographic information systems (GIS) framework. This computerized habitat model was run on the study area, Story County, Iowa, and generated a map indicating areas where wireworms were more likely to occur and where scouting should begin. Results of the model run indicate that most of Story County is suitable wireworm habitat and that there were areas considered highly favorable. The map generated by this computer model can be used as a guide for directing scouting within a field but does not identify areas where management tactics are necessary. The methodology used in this study is relatively simple, yet it performs the difficult task of combining time, space, and climatological variables to evaluate wireworm.

Makuch, J. (1998). Precision agriculture : January 1984-June 1996. [Beltsville, Md.], Water Quality Information Center of the National Agricultural Library, Agricultural Research Service, U.S. Dept. of Agriculture, [1998].

Maselli, F., M. A. Gilabert, et al. (1998). "Integration of high and low resolution NDVI data for monitoring vegetation in Mediterranean environments." Remote sens environ 63(3): 208-218.

Masser, I. (1998). Governments and geographic information. London ; Bristol, PA, Taylor & Francis, 1998. xi, 121 p. : ill., maps.

McCauley, D. (1998). "Open architecture GIS for site-specific farming." Mod agric 2(1): 26-27.

Moraghan, J. T. (1998). "Sugarbeet canopy type and accumulation of plant nitrogen as delineated by aerial photography and global positioning systems." Commun soil sci plant anal 29(19/20): 2953-2959.
Considerable within-field variation in the N content and appearance of sugarbeet (Beta vulgaris L.) leaf canopies is found often at root harvest. Since this heterogeneity can affect subsequent soil N mineralization, a study was initiated to determine if the within-field variation could be identified and located by aerial photography and a global positioning system (GPS). An aerial color photograph was taken of a commercial sugarbeet field prior to harvest. Three reflectance patterns associated with different degrees of canopy greenness ("green" [G], "yel1ow-green" [YG] and "yellow" [Y]) were identified readily. Four areas, each approximately 0.8 ha in size, with these three canopy types were selected. The canopy subsites were located by use of a GPS unit. The G, YG, and Y canopy types contained 277, 138, and 85 kg N ha-1, respectively, in sugarbeet tops. The corresponding leaf N concentrations were 30.6, 20.1, and 15.8 g kg-1, respectively. Postharvest soil NO3-N levels in the upper 120 cm of soil were 57, 14, and 10 kg ha-1 for the G, YG, and Y canopy sites, respectively. Nitrate-N in sugarbeet tops returned to the soils was at least partly responsible for the higher soil at the G subsites. In contrast to dry matter yield, recoverable sugar yield was significantly less for roots associated with the G-canopy type than for roots associated with the YG-and Y-canopy sites. Aerial photography and GPS technology can increase precision of soil testing for NO3-N after a sugarbeet crop, help to identify areas of increased soil N mineralization for a subsequent crop, and decrease subsequent N fertilizer use if a variable rate N-fertilizer applicator is used.

Nowak, P. (1998). "Agriculture and change: the promises and pitfalls of precision." Commun soil sci plant anal 29(11/14): 1537-1541.
Site specific management (SSM) (precision agriculture) holds both promises and pitfalls. Ignoring the pitfalls while only focusing on the promises can distort research activities and limit positive impacts for end users. Particular attention is given to how SSM differs from other modem production technologies that attempt to suppress or nullify ecological variation rather than respond to it. It is argued that the "homogenizing" mind-set associated with other production technologies is distorting the analytical rigor applied to developing and promoting SSM systems. A true SSM system should allow the producer to respond to ecological variation in a rational and pro-active fashion. Other promises of SSM are associated with emerging information markets, using SSM to develop risk reduction management strategies, biotechnology, and environmental protection.

Oliver, M. A. and Z. L. Frogbrook (1998). Sampling to estimate soil nutrients for precision agriculture. York, International Fertiliser Society, c1998. 36 p. : ill.

Olson, K. C. and R. C. Cochran (1998). "Radiometry for predicting tallgrass prairie biomass using regression and neural models." J range manage 51(2): 186-192.
Standing forage biomass (SFB) and the percent of standing biomass composed of forbs (PCTF) were modeled across the growing season. Samples representing stages of plant maturity from early vegetative to dormant were collected from grazed and ungrazed native tallgrass paddocks using a 0.5 X 0.5 m quadrat. Total biomass was measured during all years of the study (1992-1995). Grass and forb biomass were measured separately during 1995. Height of canopy closure also was measured during 1995. Before clipping, plots were scanned with a multispectral radiometer. Models were prepared using simple regression, multiple regression (MR), or a commercial neural network (NN) computer program. Potential inputs to MR and NN models of SFB and PCTF included Julian day of harvest (JD), range site, canopy closure height (CH), incident radiation, spectral reflectance values (RFV) at 8 discreet bandwidths, and the normalized difference vegetation index (NDVI). The NDVI alone accounted for little variability (R2 = 0.13) in SFB during all years of the study. The optimal MR model for the same data set (SFB = 3.5[JD] - 43.7[460 nm RFV] + 1099[NDVI] - 992; R2 = 0.62) accounted for a greater amount of the variability in SFB. The capacity to describe variation in SFB for the 1995 data with MR was improved when CH was included as a variable (R2 = 0.58 versus 0.78). A NN model accounted for the most variation in SFB across the entire study (R2 = 0.76). During 1995, the capability of a NN to account for variation in SFB within the training data was similar whether or not CH was included as an input (R2 = 0.86); however, prediction of SFB from validation data using the same NN was improved by using CH as an input.

Petersen, G. W., E. Nizeyimana, et al. (1998). "Applications of geographic information systems in soil degradation assessments."

Raun, W. R., G. V. Johnson, et al. (1998). "Indirect measures of plant nutrients." Commun soil sci plant anal 29(11/14): 1571-1581.
Indirect, non-destructive sensor-based methods of plant and soil analyses could replace many of the wet chemistry testing methods that are in place today. Over 140 years have past since Justus von Liebig first employed soil testing in 1850. Today, simultaneous analyses of moisture, organic carbon (C), and total nitrogen (N) in plants and soils using non-destructive near infrared reflectance spectrophotometry are possible. Recent work has targeted indirect measurements of the nutrient status in soils using spectral radiance data collected from growing crop canopies. The use of spectral measurements from plant canopies has been driven, in part, by newer variable rate technologies which apply nutrients to prescribed areas. More recent work has documented significant soil variabiliry on a 1 m2 scale. Because of this, indirect measures are necessary to avoid the cost of chemical analyses (10,000 samples required per hectare) and to avoid on-the-go chemistry. Also, in order for application technologies to be environmentally sensitive, they must treat the resolution where real differences exist in the field. Present state-of-the-art methods can sense N deficiencies in winter wheat (December - February) on a 1 m2 scale and apply variable foliar N on-the-go at 15 kph. These indirect methods rely on indices developed using the sufficiency concept that originally applied only to immobile nutrients. Plant canopy sensing methods allow for sufficiency to be used for both immobile and mobile nutrients since intensity and capacity can be integrated into one component, total nutrient uptake.

Ricotta, C., R. D. Ramsey, et al. (1998). "A fractal approach for the characterization of NOAA-AVHRR NDVI of broad scale ecoregions."

Schepers, J. S. and D. D. Francis (1998). "Precision agriculture--what's in our future." Commun soil sci plant anal 29(11/14): 1463-1469.
Introduction of new and improved technologies will speed adoption of site-specific management practices. Integrated production systems of the future will likely include more sophisticated monitoring and control devices, remote sensing, greater use of consultants and field scouts, and interactive data management systems. Professional managers and consultants will play a major role in helping producers organize data and make management decisions. Technologies that save time, result in greater profitability, and reduce environmental risks will be rapidly adopted by producers. Future opportunities will include harvesting and marketing schemes to preserve the identify of products that have special characteristics. Remote sensing will undoubtedly play a major role in helping make site-specific management decisions and in assessing world-wide marketing opportunities.

Schnug, E., K. Panten, et al. (1998). "Sampling and nutrient recommendations--the future." Commun soil sci plant anal 29(11/14): 1456-1462.
Fertile soils are one of the most important resources on earth. Sustainable agriculture should use this resource in such a way that the present and future human needs for food or other agricultural goods are warranted whereas the quality of the environment and the natural resources remain preserved. Plant production needs resources of different origins and most of them are maintained according to certain soil parameters. But as soils are neither static, nor homogenous in space and time, the standard approach of uniform application rates always results in a side by side of over and under supply. Precision Agriculture aims at addressing this spatial variability but for this task physico-chemical images [Digital Agro Resource Maps (DARM)] of the land are required. Efforts in acquiring these maps are actually one of the major bottlenecks for the exploitation of Precision Agriculture at the farm level. Most recent developments in strategies for reducing sampling efforts without loosing information are in "self surveying". This is a method by which basic spatial information of soil texture, organic matter content and geomorphology for instance are gathered just by human skills and "directed", or, "smart" sampling which uses already existing spatial information of a site to guide sampling to representative plots. Optical sensors for major important soil information like soil texture and plant available nutrients are far away from being realized. Already existing approaches for on-the-go measurements of soil features are still soil invasive and therefore slow and ineffective as far as human labor is concerned. However, these methods might benefit a lot from developments in robot techniques.

Sembiring, H., W. R. Raun, et al. (1998). "Detection of nitrogen and phosphorus nutrient status in winter wheat using spectral radiance." J plant nutr 21(6): 1207-1233.
Nitrogen (N) and phosphorus (P) are major limiting nutrient elements for crop production and continued interest lies in improving their use efficiency. Spectral radiance measurements were evaluated to identify optimum wavelengths for dual detection of N and P status in winter wheat (Triticum aestivum L.). A factorial treatment arrangement of N and P (0, 56, 112, and 168 kg N ha-1 and 0, 14.5, and 29 kg P ha-1) was used to further study N and P uptake and associated spectral properties at Perkins and Tipton, Oklahoma. A wide range of spectral radiance measurements (345-1, 145 nm) were obtained from each plot using a PSD 1000 Ocean Optics fiber optic spectrometer. At each reading date, 78 bands and 44 combination indices were generated to test for correlation with forage biomass and N and P uptake. Additional spectral radiance readings were collected using an integrated sensor which has photodiode detectors and interference filters for red and NIR. For this study, simple numerator/ denominator indices were useful in predicting biomass, and N uptake and P uptake. Numerator wavelengths that ranged between 705 and 735 nm and denominator wavelengths between 505 and 545 nm provided reliable prediction of forage biomass, and N and P uptake over locations and Feekes growth stages 4 through 6. Using the photodiode sensor, NDVI [(NIR-red)/(NIR+red)] and NR [(NIR/red)], were also good indices to predict biomass, and N and P uptake. However, no index was found to be good for detecting solely N and P concentration either using the spectrometer or photodiode sensor.

Senay, G. B., A. D. Ward, et al. (1998). "Manipulation of high spatial resolution aircraft remote sensing data for use in site-specific farming." Trans ASAE 41(2): 489-495.
Three spatial data sets consisting of high spatial resolution (1 m) remote sensing images acquired in 12 spectral bands, an on-the-go yield map, and a Digital Elevation Model were co-registered and evaluated for spatial variability studies in a Geographic Information Systems environment. Separate on-the-go yield maps were developed for 3, 5, and 12 statistically significant mean yield classes. For each yield class, the corresponding mean spectral and elevation data were extracted. The relationship between mean spectral and yield data was strongly linear (r = 0.99). Also, a strong linear relationship between mean yield and elevation data (r = 0.92) was found. The relationship between the spectral and on-the-go yield data indicated the potential of remote sensing for spatial variability studies.

Strickland, R. M., D. R. Ess, et al. (1998). "Precision farming and precision pest management: the power of new crop production technologies." J nematol 30(4): 431-435.
The use of new technologies including Geographic Information Systems (GIS), the Global Positioning System (GPS), Variable Rate Technology (VRT), and Remote Sensing (RS) is gaining acceptance in the present high-technology, precision agricultural industry. GIS provides the ability to link multiple data values for the same geo-referenced location, and provides the user with a graphical visualization of such data. When GIS is coupled with GPS and RS, management decisions can be applied in a more precise "micro-managed" manner by using VRT techniques. Such technology holds the potential to reduce agricultural crop production costs as well as crop and environmental damage.

Swinton, S. M. and J. Lowenberg DeBoer (1998). "Evaluating the profitability of site-specific farming." J prod agric 11(4): 439-446.
Site-specific farming (SSF) practices are being adopted at an accelerating rate, but evidence of their profitability has been mixed or missing. This contribution evaluates the profitability of SSF practices by synthesizing quantitative and qualitative research results within the context of the economics of information technology. The profitability results from nine published field research studies on variable rate (VR) fertilizer application are reviewed using partial budgets adjusted to include minimum costs and grid cell areas for each study. Profitability results correlated closely with the gross revenue earning potential of the crop, so VR fertilizer application was unprofitable on wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), sometimes profitable on corn (Zea mays L.), and profitable on sugarbeet (Beta vulgaris subsp. L. vulgaris). Although the formal published literature has ignored the profitability of yield mapping, production economics and farmer interviews suggest that yield mapping is profitable when it reveals yield patterns that can be managed at acceptable cost and when the information has compensating off-field value. Manageable yield variability includes not only VR input management, but also whole-field improvements such as field drainage, land leveling, windbreaks, and fencing. Off-field value can come from cheaper on-farm experimentation and greater negotiating power with landlords. Farmers and agribusinesses committed to field crop production for the long term should develop SSF capabilities. But because SSF practices are site-specific, their profitability potential too is site-specific. This site specificity extends beyond the.

Taylor, S. L., W. R. Raun, et al. (1998). "Use of spectral radiance for correcting nitrogen deficiencies and estimating soil test variability in an established bermudagrass pasture." J plant nutr 21(11): 2287-2302.
The use of variable rate technology has become increasingly popular for applying plant nutrient elements. The most widely used method for determining variable fertilizer rates is presently based on soil testing and yield mapping. Three field studies (Burneyville 1995, Burneyville 1996, and Ardmore 1996) were initiated in established Midland bermudagrass [Cynodon dacrylon (L) Pers.] pastures to determine the relationship between spectral radiance at specific wavelengths with forage nitrogen (N) removal and biomass, and to determine field variability of soil test parameters. Variable N (applied to 1.5 x 2.4 m subplots within 2.4 x 45.7 m main plots), fixed N and check treatments were evaluated at each location. Spectral radiance readings were taken in the red (671+/-6 nm), green (570+/-6 nm), and near infrared (NIR) (780+/-6 nm) wavelengths. The normalized difference vegetation index (NDVI) was calculated as NIR-red/NIR+red. Variable N rates were applied based on NDVI. The highest fixed variable N rate was set at 224, 336, and 672 kg N ha-1 for Burneyville, 1995, 1996, and Ardmore, 1996, respectively. At Burneyville, soil samples were collected in all variable rate plots (1.5 x 2.4 m) and analyzed for various soil test characteristics. NDVI, red, green, and NIR spectral radiance readings were correlated with bermudagrass forage N removal and yield. Correlation of forage yield and N removal with red, NIR, and NDVI were best with maximum forage production, however, when forage production levels were low correlation decreased dramatically for the red wavelength compared with NIR and NDVI. Forage yield and forage N removal in variable rate treatments increased when compared to the check.

Vandeveer, L. R., G. A. Kennedy, et al. (1998). "Geographic information systems procedures for conducting rural land market research." Rev agric econ 20(2): 448-461.

Viscarra Rossel, R. A. and A. B. McBratney (1998). "Soil chemical analytical accuracy and costs: implications from precision agriculture." Aust j exp agric 38(7): 765-775.

Walker, P. A. and T. Mallawaarachchi (1998). "Disaggregating agricultural statistics using NOAA-AVHRR NDVI." Remote sens environ 63(2): 112-125.

Wang, X. and Z. Y. Yin (1998). "A comparison of drainage networks derived from digital elevation models at two scales." J hydrol 210(1/4): 221-241.
Automated generation of drainage networks has become increasingly popular with powerful analytical functions in geographic information systems (GIS) and with the increased availability of digital elevation models (DEMs). This paper compares drainage networks derived from DEMs at two scales, 1:250 000 (250K) and 1:24 000 (24K), using various drainage parameters common in hydrology and geomorphology. The comparison of parameters derived from the 250K DEMs with those from the 24K DEMs in 20 basins ranging from 150 to 1000 km2 in West Virginia shows that the goodness-of-fit between parameter estimates based on the DEMs varies. Results clearly show that superior estimations are produced from the 24K DEMs. Better estimates can be obtained from the 250K DEMs for stream length and frequency parameters than for gradient parameters. However, the estimation of the mean gradient parameters based on the 250K DEMs seems to improve with increasing terrain complexity. Finally, basin size does not strongly affect the accuracy of parameter estimates based on the 250K DEMs.

White, J. L., J. C. Whitcraft, et al. (1998). "A variable variety grain drill for wheat production." Appl eng agric 14(1): 7-17.
A variable variety grain drill, with the ability to plant three different varieties of grain, was constructed and tested. Switching of each variety of grain was controlled by a computer which used the global positioning system (GPS) as a locator. The grain drill was used to ground proof the accuracy of the spatially variable application of fertilizer, also controlled by a computer using GPS as a locator, through the placement of different seeds rather than different liquid nitrogen rates. Lentils, oats, and peas were planted in a grid on a small plot and measurements were taken from the surveyed grid to determine the accuracy of placement. An average switching accuracy of 5.5 m (18 ft) was found at 7.2 km/h (4.5 mph). The maximum error was 20 m (66 ft) which was adequate for large fields of cereal grains. Reduced computer sampling times were suggested for reducing the error. The feasibility of varying varieties of wheat based on slope position was also investigated through a field study using Basin, Eltan, and Madsen cultivars of winter wheat and a blend of the three varieties. These varieties were selected because Basin is lodging resistant, Madsen is a higher yielding cultivar and Eltan is winter hardy. Yields were compared based on slope position and aspect and were used along with other studies found in the literature to determine the feasibility of varying the winter wheat variety based on slope position. From this it was determined that Basin or Madsen should be used at the toe slope, Madsen or a mix should be selected at the midslope, and any of the varieties could be used at the ridge top position. Therefore, Madsen could have been used alone as effectively as varying the varieties.

Wilson, J. P., D. J. Spangrud, et al. (1998). "Global positioning system sampling intensity and pattern effects on computed topographic attributes." Soil Sci Soc Am j 62(5): 1410-1417.
Global positioning system (GPS) and digital elevation model (DEM) technologies can provide measurements of terrain attributes that influence soil processes, soil properties, and site-specific management. We hypothesized that the intensity and pattern of sampling points affects the computed contour maps and topographic attributes. The intensity and pattern of sampling points, selected from 6284 GFS-derived x, y, z values, were varied to test this hypothesis on estimated elevations and topographic attributes in a 20-ha Montana farm field. Variations of 0.05% in mean elevation between the sample and reference grids generated less than or equal to 25% differences in slope gradients, less than or equal to 38% in specific catchment area, and less than or equal to 22% in steady-state topographic wetness index. Errors diminished as sample size (resolution) and distribution (spread) increased. Overall, the results demonstrate how relatively small differences in elevations at individual points (locations) in a landscape may mask large variations in the resultant shapes and hydrologically important topographic attributes calculated from DEMs. The intensive sampling may be practical where vehicle-mounted GPS can traverse cultivated fields, but impractical in trees and rough terrain.

Yang, D. S., B. C. Pijanowski, et al. (1998). "Analysis of gypsy moth (Lepidoptera: Lymantriidae) population dynamics in Michigan using geographic information systems." Environ entomol 27(4): 842-852.
We studied the 9-yr (1986-1994) statewide gypsy moth, Lymantria dispar (L.), population distribution dynamics in Michigan using geographic information systems (GIS) based on an analysis of pheromone trap data of male moth catch from more than 3,000 permanent sites. A time series of male moth contour maps with 7 density categories (0, 1-25, 26-100, 101-200, 201-300, 301-400 and >400 moths (.) trap-1 (.) year-1) was created using the GIS. The statewide gypsy moth population expanded at an alarming rate of 6,053 km2/yr with the largest area infested being 128,164 km2 (85% of the state) in 1993. The population-weighted mean center stayed in the Lower Peninsula, but a low density population was developing in the Upper Peninsula during the 9-yr period. Map analysis showed that the statewide population gradually increased from 1986 to 1990 and then became relatively stable thereafter. Both the highest weighted average density (191 moths (.) trap 1 (.) year-1) and the greatest coefficient of relative dispersion (307%) occurred in 1990. Linear regression slopes between successive years were >1.0 before 1990 and <1.0 thereafter, indicating an increasing and then decreasing population density change. Regression results between successive years indicate that the previous years' population map is a good linear approximation for the following (r2 > 70%). In the 9-yr study, 55% of the population cells stayed in the same density class in the following year. A general pattern of population density shifts was that increase prevailed over decrease. Research methodology, population distribution, temporal dynamics, and density shifts are discussed.

Yang, C., C. L. Peterson, et al. (1998). "Spatial variability of field topography and wheat yield in the Palouse region of the Pacific Northwest." Trans ASAE 41(1): 17-27.
Measurement and analysis of the spatial variability of fields are two important aspects of site-specific crop management. In this study, data for wheat yield, g round slope and aspect were intensively collected from five fields in the Palous e region of Washington using a set of sensors and a Global Positioning System (G PS) receiver. A Geographic Information System (GIS) database was developed to ma nage the field-collected data and information from topographic maps and to group the data from each field into different regions for analysis. Relative elevatio n differences across the five fields ranged from 29 to 70 m. Slope steepness ran ged from 0 to 30 degrees with field means of 9 to 12 degrees. Geostatistical ana lyses showed that the spatial patterns of variability in wheat yields differed n ot only from one field to another but also from one region to another within a f ield. The ranges of influence in wheat yield for the five whole fields were from 55 to 86 m, while those for the within-field regions varied from 20 to over 100 m. Regression analyses indicated that topographic attributes including elevatio n, slope and aspect had significant effects on wheat yield. These topographic at tributes could explain 13 to 35% of the variability in wheat yield for the whole fields, though 49 to 84% of the yield variability could be explained by topogra phy in some regions within the five fields. These results provided useful quanti tative information about the influence of topography on crop yield in the Palous e region.

Yang, L., B. K. Wylie, et al. (1998). "An analysis of relationships among climate forcing and time-integrated NDVI of grasslands over the U.S. northern and central Great Plains." Remote sens environ 65(1): 25-37.

Yu, M., E. Segarra, et al. (1998). "The economics of soil fertility under precision agriculture: the case of phosphorus." Proc Beltwide Cotton Conf 1: 289-292.

(1999). Precision agriculture curriculum : curriculum guide. 1st ed. [Iowa], Precision Agriculture Education Network, 1999. 16 leaves 1 computer optical disc (4 3/4 in.).

(1999). A growing career in crop production. St. Louis, MO, The Association, [1999] 1 videocassette (12 min.) : sd., col.
Describes the career of an agricultural custom applicator and the knowledge and training needed for the position.

(1999). Precision agriculture. Boston, Kluwer Academic, [1999- v. : ill.

Adamchuk, V. I., M. T. Morgan, et al. (1999). "An automated sampling system for measuring soil pH." Trans ASAE 42(4): 885-891.
Within the scope of precision farming there is a need for improved methods of assessing and managing soil variability. The site-specific management of soil pH is one application that has potential benefits for crop production. However, current grid sampling and mapping techniques to estimate lime requirement may not be adequate. For this reason, an automated soil sampling system for measuring soil pH on-the-go has been created. The system includes a computer-operated soil sampling mechanism mounted in a shank, a global positioning unit, and a pH meter with a flat surface electrode. The system measures soil pH directly on a sample. The automated soil sampling system can determine pH while taking soil samples at a selected depth (0-20 cm) every 8 s. A simple linear regression was used to calibrate the electrode mV output against soil pH obtained via a standard laboratory method. Field testing yielded an r(2) of 0.83 and a standard error of prediction of 0.45 pH.

Adamsen, F. J., P. J. Pinter, Jr., et al. (1999). "Measuring wheat senescence with a digital camera." Crop sci 39(3): 719-724.
Documenting crop senescence rates is often difficult because of the need for frequent sampling during periods of rapid change and the subjective nature of human visual observations. The purpose of this study was to determine the feasibility of using images produced by a digital camera to measure the senescence rate of wheat and to compare the results with changes in greenness determined by two established methods. Measurements were made as part of an experiment to determine the effects of elevated CO(2) and limited soil nitrogen on spring wheat (Triticum aestivum L.) at the University of Arizona's Maricopa Agricultural Center, near Phoenix, AZ. "Greenness" measurements were made during senescence of the crop with a color digital camera, a hand-held radiometer, and a SPAD chlorophyll meter. The green to red (G/R) for each pixel in an image was calculated and the average G/R computed for cropped images from a digital camera representing 1 m(2) for each treatment and sample date. The normalized difference vegetation index (NDVI) was calculated from the red and near-infrared canopy reflectances measured with a hand held radiometer. A SPAD reading was obtained from randomly selected flag leaves. All three methods of measuring plant greenness showed similar temporal trends. The relationships between G/R with NDVI and SPAD were linear over most of the range of G/R. However, NDVI was more sensitive at low values than G/R. G/R was more sensitive above G/R values of 1.2 than SPAD because the upper limits of SPAD measurements were constrained by the amount of chlorophyll in the leaf, while G/R responded to both chlorophyll concentration in the leaves as well as the number of.

Akins, D. C., J. L. Willers, et al. (1999). "Integrating GIS into precision crop management." Proc Beltwide Cotton Conf 1: 395-399.

Al Gaadi, K. A. and P. D. Ayers (1999). "Integrating GIS and GPS into a spatially variable rate herbicide application system." Appl eng agric 15(4): 255-262.
A spatially variable rate herbicide application system was developed and a site-specific evaluation of its field performance and accuracy was conducted. A 4.2-ha (10.4-ac) field was sampled on an 18.3-m (60-ft) grid for soil type and organic matter percent (OM%). A herbicide management table was used to determine the appropriate active ingredient (AI) application rate for each area of the field depending on spatial variation of field parameter data (soil type and OM%). Application rate of AI varied from 3510 mL/ha (1.5 qt/ac) up to 5260 mL/ha (2.25 qt/ac). Using geographical information system (GIS) software, a georeferenced map (management map) of field application rates was produced. A direct nozzle injection field sprayer was equipped with a real-time differentially corrected global positioning system (DGPS). A program was developed to receive on-the-go the sprayer position data (latitude and longitude) and retrieve the desired application rate from the GIS map at the current sprayer field position. A datalogger was used to change on-the-go the AI flow rate (water was used as a substitute for the AI) to correspond with the desired application rate at a specific sprayer ground speed and field position. To evaluate the system accuracy in reproducing the management map, data was collected from the DGPS to determine its field accuracy. DGPS data and datalogger output (data produced by sprayer monitoring sensors) along with the GIS map were utilized to reveal the spatial accuracy of the application system. Control system reaction time and accuracy were investigated using data from the datalogger program output. Results revealed that the DGPS maintained an.

Arslan, S. and T. S. Colvin (1999). "Laboratory performance of a yield monitor." Appl eng agric 15(3): 189-195.
Response of a yield sensor to know grain flow variations was investigated under laboratory operating conditions through comparison with an electronic scale mounted oil a test stand. The yield sensor had a quick response to sudden changes in corn flow. Based on total weight comparisons, the average percent error at constant flow rates was 2.1%. The error increased to 3.2% and 4.3% when step inputs and transients were applied, respectively. The overall accuracy was within the accuracy range (+/- 4%) reported by the manufacturer while the maximum error was more than 5%. The flow rate range used in the calibration was the most important factor in achieving high accuracy. Because of the fluctuations in estimated flow rate, a single data point did not correlate well with the actual grain flow rate. Averaging over 4 to 6 s usually resulted in an error less than 4%. When the flow rate varied more profoundly during steps and transients, approximately 10 s averaging was needed to maintain the accuracy in some of the tests. The effects of potential sources of errors (such as varying combine ground speed, changing crop conditions, and varying grain flow profile) also need to be considered to use the results of this study for field applications.

Atherton, B. C., M. T. Morgan, et al. (1999). "Site-specific farming: a perspective on information needs, benefits and limitations." J soil water conserv 54(2): 455-461.

Atkinson, P. M. and N. J. Tate (1999). Advances in remote sensing and GIS analysis. Chichester ; New York, Wiley, c1999. xiv, 273 p. : ill. (some col.).

Blackmore, S. and M. Moore (1999). "Remedial correction of yield map data." Precis agric 1(1): 53-66.
Many yield maps exhibit systematic errors that attenuate the underlying yield variation. Two errors are dealt with in detail in this paper: those that occur when the harvester has a narrow finish to a land and those that occur when the harvester is filling up at the start of a harvest run. The authors propose methods to correct or remove erroneous data by the use of an expert filter, or alternatively use of an interpolation technique called potential mapping.

Bouma, J., J. Stoorvogel, et al. (1999). "Pedology, precision agriculture, and the changing paradigm of agricultural research." Soil Sci Soc Am j 63(6): 1763-1768.
Precision agriculture (PA) has recently been defined by the U.S. National Research Council as a management strategy that uses information technologies to bring data from multiple sources to bear on decisions associated with crop production. Soil information is important here, but current soil survey data do not satisf PA requirements. In this paper, the need for soil data in PA is discussed on the basis of Dutch research. Not only operational, but also tactical and strategic aspects are considered. On the operational level, soil data, including parameters derived with pedotransfer functions, support the use of simulation models to quantify dynamically soil water regimes, N transformations, and biocide adsorption. Real time "forward-looking" simulations incorporated in early-warning systems assist in operational decisions on water, nutrient, and crop protection management. Backward-looking simulations, using historic weather data, can be used to evaluate different management tactics for exploratory strategic and tactical purposes. Such simulations should balance production and environmental requirements. At the strategic and tactical level, assembled data on the performance of various farm management systems should be grouped by soil series to build a systematic database, allowing "quick and preliminary" evaluations of the effects of farm management strategies based on experiences obtained elsewhere on similar soils.

Boydell, B., G. Vellidis, et al. (1999). "Deconvolution of site-specific yield measurements to address peanut combine dynamics." Trans ASAE 42(6): 1859-1865.
During the development of a peanut yield monitoring system, experiments were conducted on a two-row peanut combine to determine the duration of time lag between pickup and yield measurement, and to characterize the convolution of peanut flow within the combine. The research indicates that the two-row peanut combine used in the experiment subjects harvested product to significant convolution. A simple time lag correction will not recover the site specific (short term accuracy) of yield measurements. The distance and time period required to achieve a yield estimate error less than 20% (95% confidence) is greater than 19.7 m (17 s) for simple time lag correction while it is 5.8 m (5 s) for deconvoluted data. The net result is that smaller regions of yield variability may be recognized with greater confidence using the deconvolution method than with the simple time delay method.

Cambardella, C. A. and D. I. Karlen (1999). "Spatial analysis of soil fertility parameters." Precis agric 1(1): 5-14.
Databases identifying spatial distributions of soil properties are needed to implement site-specific management practices. This study examined spatial patterns for nine soil chemical properties in two adjacent fields, one in a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation with inorganic fertilizer and the other in a 5-yr corn-soybean-corn-oat (Avena sativa L.)-meadow rotation with organic nutrient sources. We established sampling grids in both fields and collected soil cores to a depth of 30 cm. Soil properties with strong spatial correlations (low nugget variance/total variance ratio) and the maximum distance to which those properties were correlated (range) differed for the two fields. Soil pH, exchangeable Ca, total organic C, and total N were strongly correlated and had range values greater than 182 m in the conventional field. Bray P and exchangeable Mg were strongly correlated with range values of less than 100 m within the other. Low nugget/total variance ratios and small range values for P and Mg suggest patchy distributions, probably from long-term animal manure and municipal sludge application. Since most variance was structural in the organic field, placing sampling points closer together would improve data precision. In contrast, a relatively coarse sampling grid with fewer sampling points spaced further apart appears adequate for the conventional field. To develop accurate sampling strategies for precision agriculture, long-term field management histories should be documented since the practices appear to affect both the properties that are strongly correlated and the range to which the correlation exists.

Cassman, K. G. (1999). "Ecological intensification of cereal production systems: yield potential, soil quality, and precision agriculture." Proc Natl Acad Sci U S A 96(11): 5952-5959.
Wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) provide about two-thirds of all energy in human diets, and four major cropping systems in which these cereals are grown represent the foundation of human food supply. Yield per unit time and land has increased markedly during the past 30 years in these systems, a result of intensified crop management involving improved germ-plasm, greater inputs of fertilizer, production of two or more crops per year on the same piece of land, and irrigation. Meeting future food demand while minimizing expansion of cultivated area primarily will depend on continued intensification of these same four systems. The manner in which further intensification is achieved, however, will differ markedly from the past because the exploitable gap between average farm yields and genetic yield potential is closing. At present, the rate of increase in yield potential is much less than the expected increase in demand. Hence, average farm yields must reach 70-80% of the yield potential ceiling within 30 years in each of these major cereal systems. Achieving consistent production at these high levels without causing environmental damage requires improvements in soil quality and precise management of all production factors in time and space. The scope of the scientific challenge related to these objectives is discussed. It is concluded that major scientific breakthroughs must occur in basic plant physiology, ecophysiology, agroecology, and soil science to achieve the ecological intensification that is needed to meet the expected increase in food demand.

Chan, K. (1999). Digest : a primer for the international GIS standard. Boca Raton, Fla., Lewis Publishers, c1999. 128 p. : ill.

Choubey, V. K. and R. Choubey (1999). "Spectral reflectance, growth and chlorophyll relationships for rice crop in a semi-arid region of India." Water resour manag 13(2): 73-84.
Relations among spectral reflectance, chlorophyll 'a', and growth of rice plants grown on irrigated light textured soil in a semi arid region are presented here. There was a linear relation between spectral reflectance and rice plant height (r = 0.97), for band 1 (0.45-0.52 micrometers) reflectance values. On the other hand, in bands 2 (0.52-0.60 micrometers) and 3 (0.63-0.69 micrometers), reflectance values decreased until 70 days after planting (DAP) and then increased during the reproductive phase of the crop. The near infrared band 4 (0.76-0.90 micrometers) showed a maximum reflectance at 59 DAP (panicle initiation stage) and a decline in reflectance thereafter through maturity. The peak value of IR/R ratio was 16.39 at 62 DAP during the early reproductive phase; thereafter, it declines gradually with the maturity of the crop. Chlorophyll 'a' concentration was high during early growth (vegetative and early reproductive stages) and decreased during the flowering and maturity stages. The rice plant canopy show a high chlorophyll 'a' concentration at 64 and 59 DAP for sites A and B, respectively. Chlorophyll 'a' concentration is higher in site A plant canopies than it is in site B during the entire crop cycle. A good inverse correlation (r = 0.91) has been found between chlorophyll 'a' and band 1, while the IR/R ratio and the normalised difference vegetation index (NDVI) showed a relationship (r = 0.78) with the chlorophyll 'a' concentration during the crop cycle. Band 2, 3 and 4 radiance values show a biphasic linear relationship with chlorophyll 'a' concentrations, negative for early growth and positive for flowering and maturity stages. Results indicate that the period between 66.

Cridland, S. (1999). Seasonal intelligence for rangeland managers using NOAA-NDVI data : a report for the Rural Industries Research and Development Corporation. Barton, ACT, RIRDC, 1999. xii, 85 p. : col. ill., col. maps.

Cunningham, C. J. (1999). "Monitoring yield in wine grapes." Calif grow 23(3): 7-8.

DeHaan, K. R., G. T. Vessey, et al. (1999). "Relating potato yield to the level of soil degradation using a bulk yield monitor and differential global positioning systems." Comput electron agric 23(2): 133-143.
The adoption of soil conservation practices is often dependent on linking reductions in crop productivity to declines in soil and land quality. A bulk yield monitoring system was installed on a commercial potato harvester for the purpose of showing a relationship between potato yield and the level of degradation on fine sandy loam soils (Orthic Podzols) in the cool, humid climate of Prince Edward Island, Atlantic Canada. Although data are preliminary, initial results indicate that potato yields will be substantially reduced as a result of soil physical properties being altered by excessive long-term soil degradation. Significant correlations were identified between potato yield and a number of physical factors representative of soil degradation including the slope length and steepness factor, cation exchange capacity, depth of topsoil and water holding capacity. If, after confirmation from further study, the relationship between potato yield and the level of soil degradation can be quantified, it will provide a valuable tool in terms of encouraging farmers to adopt soil conserving practices.

DeTar, W. R., S. J. Maas, et al. (1999). "Drip vs. furrow irrigation of cotton on sandy soil with 1/4 mile runs--includes: yield monitoring, remote sensing, and electronic soil survey." Proc Beltwide Cotton Conf 1: 375-380.

Dobermann, A. and P. F. White (1999). "Strategies for nutrient management in irrigated and rainfed lowland rice systems." Nutr cycl agroecosyst 53(1): 1-18.

Drummond, S. T., C. W. Fraisse, et al. (1999). "Combine harvest area determination by vector processing of GPS position data." Trans ASAE 42(5): 1221-1227.

Ehsani, M. R., S. K. Upadhyaya, et al. (1999). "A NIR technique for rapid determination of soil mineral nitrogen." Precis agric 1(2): 217-234.
The objective of this investigation is to determine the possibility of rapidly sensing soil mineral-N content using near infrared (NIR) reflectance. Simulation studies were conducted to determine the ability of Partial Least Squares (PLS) and Principal Components Regression (PCR) techniques to relate NIR spectral data to soil nitrate content in the presence of interfering effects and experimental noise. The simulation studies revealed that both PLS and PCR techniques were quite robust in predicting soil nitrate content provided the calibration set included the same interfering effects. These techniques failed completely if the prediction set contained interfering effects which were not included in the calibration set. This implies that a site-specific calibration is necessary for this technique to work successfully. Laboratory tests using Yolo loam and Capay clay soil samples as well as verification tests using field soils (Yolo loam and Capay clay) mixed with nitrogen fertilizer indicated that soil mineral-N content can be determined using the NIR technique provided site-specific calibration is used.

Fleischer, S. J., P. E. Blom, et al. (1999). "Sampling in precision IPM: when the objective is a map." Phytopathology 89(11): 1112-1118.
Measuring and understanding spatial variation of pests is a fundamental component of population dynamics. The resulting maps can drive spatially variable pest management, which we define as precision integrated pest management (IPM). Precision IPM has the potential to reduce insecticide use and slow the rate of resistance development because of the creation of temporally dynamic refuges. This approach to IPM requires sampling in which the objective is to measure spatial variation and map pest density or pressure. Interpolation of spatially referenced data is reviewed, and the influence of sampling design is suggested to be critical to the mapped visualization. Spatial sampling created problems with poor precision and small sample sizes that were partially alleviated with choosing sampling units based on their geostatistical properties, adopting global positioning system technology, and mapping local means. Mapping the probability of exceeding a threshold with indicator kriging is discussed as a decision-making tool for precision IPM. The different types of sampling patterns to deploy are discussed relative to the pest mapping objective.

Gold, M. V. (1999). Geographic information systems (GIS) and agriculture : environmental applications. Beltsville, MD, Alternative Farming Systems Information Center, National Agricultural Library, Agricultural Research Service, USDA, [1999?].

GopalaPillai, S. and L. Tian (1999). "In-field variability detection and spatial yield modeling for corn using digital aerial imaging." Trans ASAE 42(6): 1911-1920.
High-resolution color infrared (CIR) images acquired with an airborne digital camera were used to detect in-field spatial variability in soil type, crop nutrient stress, and to analyze spatial variability in yield. Images were processed using an unsupervised learning (clustering) method. The clustered images were geo-referenced, and spatially analyzed using a GIS package. The image patterns in a processed image of bare soil matched well with soil type map with 76% accuracy. The CIR images of a cornfield indicated nitrogen stress areas from 75 days after planting (DAP). The CIR reflectance was better correlated to the yield after pollination of corn compared to the early images. The spatial variation in yield was linearly correlated to the spatial variation of individual reflectance bands (NIR, R, and G) as well as normalized intensity (NI) of CIR image. Spatial yield models on uncalibrated reflectance bands of image could predict 76 to 98% of yield variation in each field. A linear regression model on NI developed from one field image predicted yield with an accuracy of 55 to 91% in different fields and seasons. Digital aerial imaging proves to be a promising tool for obtaining spatial in-field variability in the crop field for site-specific management and yield prediction.

Gummer, J. S., B. Higgs, et al. (1999). Keynote address and discussion, 7th annual conference : 'Precision agriculture - practical applications of new technologies'. York, International Fertiliser Society, c1999. 28 p.

Gupta, R. K., S. Mostaghimi, et al. (1999). "Modeling spatial variability of soil chemical parameters for site-specific farming using stochastic methods." Water air soil pollut 110(1/2): 17-34.

Gyldenkaerne, S., B. J. M. Secher, et al. (1999). "Ground deposit of pesticides in relation to the cereal canopy density." Pestic sci 55(12): 1210-1216.
Pesticides not reaching the intended target may have negative effects on the environment and the field ecosystem. To estimate the potential ground water pollution and risk for soil-dwelling organisms it is necessary to estimate the amount of pesticide reaching the soil in different spraying situations. Literature shows that ground deposition may vary even within equal growth stages due to variations in canopy density. This paper discusses the feasibility of estimating the ground deposition of pesticides from canopy density in cereal fields. Spray experiments were carried out in wheat and barley with flat-fan nozzles of two sizes. Differences of ground deposition between the two nozzle sizes were insignificant. Adding surfactant to the spray solution significantly reduced the soil deposition in barley and in wheat cv Sleipner but not in cv Haven. A significant effect of Leaf Area Index (LAI) on ground deposition was obtained. A simple exponential model based on the LAI with an extinction coefficient of 0.48-0.50 may for many occasions satisfactorily describe the soil deposition of pesticides in cereals. Using non-destructive LAI-measurements combined with the deposition model may be useful in pesticide risk assessment on field, farm and larger regional scale and is optimizing the application rate in site-specific farming.

Hallam, C. A. and J. M. Salisbury (1999). Geographic Information Systems (GIS) applications in water resources research : American Water Resources Association Annual Meeting, Chicago, Illinois, November 6-10, 1994. [Reston, Va.?], U.S. Dept. of the Interior, U.S. Geological Survey, National Mapping Division, [1999?] ii, 32 leaves.

Hartkamp, A. D., J. W. White, et al. (1999). "Interfacing geographic information systems with agronomic modeling: a review." Agron j 91(5): 761-772.

Hartkamp, A. D. (1999). Interpolation techniques for climate variables. Mexico, CIMMYT, 1999. vi, 26 p. : ill. (some col.), maps (some col.).

Heiniger, R. W. (1999). "Understanding geographic information systems and global positioning systems in horticultural applications." HortTechnology 9(4): 539-547.
New technologies such as differential global positioning systems (DGPS) and geographical information systems (GIS) are making it possible to manage variability in soil properties and the microenvironment within a field. By providing information about where variability occurs and the patterns that exist in crop and soil properties, DGPS and GIS technologies have the potential of improving crop management practices. Yield monitoring systems linked to DGPS receivers are available for several types of horticultural crops and can be used in variety selection and/or improving crop management. Precision soil sampling and remote sensing technologies can be used to scout for infestations of insects, diseases, or weeds, to determine the distribution of soil nutrients, and to monitor produce quality by measuring crop vigor. Combined with variable rate application systems, precision soil sampling and remote sensing can help direct fertilizer, herbicide, pesticide, and/or fungicide applications to only those regions of the field that require soil amendments or are above threshold levels. This could result in less chemical use and improved crop performance. As with any information driven system, the data must be accurate, inexpensive to collect, and, most importantly, must become part of a decision process that results in improvements in crop yield, productivity, and/or environmental stewardship.

Heisel, T., A. K. Ersboll, et al. (1999). "Weed mapping with co-kriging using soil properties." Precis agric 1(1): 39-52.
Our aim is to build reliable weed maps to control weeds in patches. Weed sampling is time consuming but there are some shortcuts. If an intensively sampled variable (e.g. soil property) can be used to improve estimation of a sparsely sampled variable (e.g. weed distribution), one can reduce weed sampling. The geostatistical estimation method co-kriging uses two or more sampled variables, which are correlated, to improve the estimation of one of the variables at locations where it was not sampled. We did an experiment on a 2.1ha winter wheat field to compare co-kriging using soil properties, with kriging based only on one variable. The results showed that co-kriging Lamium spp. from 96 0.25m2 sample plots ha-1 with silt content improved the prediction variance by 11% compared to kriging. With 51 or 18 sample plots ha-1 the prediction variance was improved by 21 and 15%.

Kitchen, N. R., K. A. Sudduth, et al. (1999). "Soil electrical conductivity as a crop productivity measure for claypan soils." J prod agric 12(4): 607-617.
Inexpensive and accurate methods for spatially measuring soil properties are needed that enhance interpretation of yield maps and improve planning for site-specific management. This study was conducted to investigate the relationship of apparent profile soil electrical conductivity (EC(a)) and grain yield on claypan soils (Udollic Ochraqualfs). Grain yield data were obtained by combine yield monitoring and EC(a) by a mobile, on-the-go electromagnetic (EM) induction meter. Investigations were made on four claypan fields between 1993 and 1997 for a total of 13 site-years. Crops included five site-years of corn (Zea mays L.), seven site-years of soybean [Glycine max (L.) Merr.], and one site-year of grain sorghum [Sorghum bicolor (L) Moench]. Transformed EC(a) (1/EC(a)) was regressed to topsoil thickness giving r(2) values > 0.75 for three of the four fields. The relationship between grain yield and EC(a) was examined for each site-year in scatter plots. A boundary line using a log-normal function was fit to the upper edge of data in the scatter plots. A significant relationship between grain yield and EC(a) (boundary lines with r(2) > 0.25 in nine out of 13 site-years) was apparent, but climate, crop type, and specific field information was needed to explain the shape of the potential yield by EC(a) interaction. Boundary line data of each site-year fell into one of four condition categories: Condition 1 site-years where yield increased with decreasing EC(a); Condition 2 site-years where yield decreased with decreasing EC(a); Condition 3 where yield was less at low and high EC(a) values and highest at some mid-range values of EC(a); and Condition 4 site-years.

Lee, W. S., D. C. Slaughter, et al. (1999). "Robotic weed control system for tomatoes." Precis agric 1(1): 95-113.
A real-time intelligent robotic weed control system was developed for selective herbicide application to in-row weeds using machine vision and precision chemical application. The robotic vision system took 0.34s to process one image, representing a 11.43 cm by 10.16 cm region of seedline containing 10 plant objects, allowing the prototype robotic weed control system to travel at a continuous rate of 1.20 km/h. The overall performance of the robotic system in a commercial processing tomato field and in simulated trials is discussed.

Lee, B. D., J. A. Wald, et al. (1999). "Introducing students to online county soil surveys and the STATSGO database using GIS." J nat resour life sci educ 28: 93-96.
Technological advances have allowed natural resource information to become available in large databases over the Internet. We have developed a laboratory exercise that introduces students to geographic information systems (GIS) and soil and landuse databases available from the Natural Resource Conservation Service (NRCS), National Survey Database Access Facility. The exercise involves an introduction to spatial data using the State Soil Geographic (STATSGO) database and county soil surveys using a prototype survey of the Dade County area, Florida. In addition, students are introduced to the concept of scale by identifying land use problems utilizing online county soil survey data (1:12000 to 1:63360) and STATSGO data (1:250000). Students had difficulty using the online soil survey due to the absence of map sheets and quickly identified the advantages of spatially referenced data available from STATSGO, which was viewable in map form using GIS software. This laboratory exercise introduced an application of GIS, spatial data available from the NRCS, and online soil surveys to introductory soil science students to solve a hypothetical regional planning problem. In addition to enhancing students' interests in GIS and associated technology, the exercise effectively demonstrated scale differences by comparison of information available from the STATSGO database and county soil surveys.

Lowell, K. and A. Jaton (1999). Spatial accuracy assessment : land information uncertainty in natural resources. Chelsea, Mich., Ann Arbor Press, c1999. xiv, 455 p. : ill., maps.

Lukina, E. V., M. L. Stone, et al. (1999). "Estimating vegetation coverage in wheat using digital images." J plant nutr 22(2): 341-350.
No method exists to reliably predict percent vegetation coverage using indirect measures. This study was conducted to evaluate the use of digital image processing techniques applied to digital color, red-green-blue (RGB), images of crop canopies to estimate percent vegetation coverage and biomass. Two field experiments with winter wheat (Triticum aestivum L.) "Tonkawa" were planted in October 1996 and 1997 at Perkins, OK on a Teller sandy loam (Udic Argiustoll) and at Tipton, OK on a Tipton silt loam (Pachic Argiustoll). Plot images from winter wheat canopies were taken using a Kodak DC40 Digital Camera (1995) with an image resolution of 756 x 504 pixels. Spectral irradiance readings were taken from wheat canopies in red (671 +/- 6 nm) and near infrared (780 +/- 6 nm) wavelengths, and normalized difference vegetation index (NDVI) was calculated. Percent vegetation coverage was estimated using image-processing routines in Micrografx Picture Publisher version 7.0. The digital images were converted from 8-bit RGB tagged image file format (TIFF) files, which were produced by processing the images from the camera with Photo Enhancer, to binary pseudo-color images. Percent of pixels corresponding to the vegetation color was then calculated and used as the percent coverage for each plot. Binary pseudo-color images provided useful estimates of percent vegetation coverage that were highly correlated with wheat canopy NDVI measurements.

McBratney, A. B. and M. J. Pringle (1999). "Estimating average and proportional variograms of soil properties and their potential use in precision agriculture." Precis agric 1(2): 125-152.
Precision Agriculture requires a method of gathering information about the spatial variability of soil that reduces the need for expensive and intensive sampling. This can be achieved through the use of what we term 'average' and 'proportional' variograms. A literature search has enabled the gathering of variograms for multiple soil properties, allowing comparison of the magnitude of variability and the construction of averages. For soil properties that display proportionality between their mean squared and variance, the variogram can be predicted from a mean value. These average and proportional variograms are potentially beneficial to implementers of Precision Agriculture as they can be used to plan optimal soil sampling and management schemes. It was found that if wishing to implement site-specific management to a resolution of 20 x 20 m then grid soil sampling will generally have to be performed at 20-30 m intervals depending on the attribute of interest. A decision-support chart for differential soil management based on a variogram's comparative magnitude to the average is presented. Further work needs to be done on increasing the data base these results are based on and refining the proportional variogram parameters to site-specificity.

McCauley, J. D. (1999). "Simulation of cotton production for precision farming." Precis agric 1(1): 81-94.
Most crop simulation models do not directly consider the spatial variability of inputs nor do they produce outputs that show the expected spatial variability of yield across a field. If such models were available for precision farming, then researchers could much better evaluate the effects of soil sampling densities to determine the number of samples necessary to adequately model a particular field. The objectives of this study were: (1) to design and implement a spatial simulation methodology for examining details of precision farming and (2) use this to evaluate the effects of different soil sampling resolutions on predicted yield and residual nitrates through spatially variable nitrogen applications. The COSSYM/COMAX cotton growth model/expert system and the GRASS geographic information system were used to develop a spatial simulation that produces spatially variable outputs. Inputs to the model were collected from a 3.9-ha cotton field. Soil nitrate, a primary driver in fertilizer recommendations, was sampled on a 15.2-m regular grid for depths to 15-cm and on a 30.5-m regular grid at six 15-cm depth intervals (down to 90 cm). COMAX was used to determine spatially variable fertilizer recommendations. GOSSYM was used to simulate perfect application of these recommendations and predicted spatially variable yield and residual nitrates. Reductions in sampling density or resolution were simulated by systematically reducing the amount of data available to COMAX for calculating spatially variable fertilizer recommendations. GOSSYM subsequently used these recommendations (based upon less and less knowledge of soil nitrates) to simulate the effects of differing sampling resolutions on predicted.

Melancon, P. A., D. R. Maidment, et al. (1999). A GIS based watershed analysis system for Tillamook Bay, Oregon. Austin, Tex., Center for Research in Water Resources, University of Texas at Austin, c1999.

Meyer, G. E. and J. A. DeShazer (1999). Precision agriculture and biological quality : 3-4 November 1999, Boston, Massachusetts. Bellingham, Wash., USA, SPIE, c1999. ix, 390 p. : ill.

Miller, W. M. and J. D. Whitney (1999). "Evaluation of weighing systems for citrus yield monitoring." Appl eng agric 15(6): 609-614.

Moore, G. A. and J. P. Tyndale Biscoe (1999). "Estimation of the importance of spatially variable nitrogen application and soil moisture holding capacity to wheat production." Precis agric 1(1): 27-38.
Crop growth modelling techniques were used to investigate the performance of a wheat crop over a range of weather conditions, nitrogen application rates and soil types. The data were used to predict long term benefits of using spatially variable fertilizer application strategies where fertilizer application rate was matched to the soil type, against a strategy of uniform fertilizer application. The model was also run with modified soil properties to determine the importance of soil moisture holding capacity in the variability of crop yield. It was found that the benefits of spatially variable nitrogen management when fertilizer was applied at the beginning of the season were modest on average. The range of results for different weather conditions was much greater than the average benefit. A large proportion of the variability of crop performance between soil types could be explained by differing soil moisture holding capacity. Devising techniques for managing this variability was concluded to be important for precision farming of cereals.

Morain, S. A. (1999). GIS solutions in natural resource management : balancing the technical-political equation/. 1st ed. Santa Fe, NM, OnWord Press, 1999. xix, 364 p. : ill., maps.

Morris, D. K., D. R. Ess, et al. (1999). "Development of a site-specific application system for liquid animal manures." Appl eng agric 15(6): 633-638.

Nelson, C. J. (1999). "Managing nutrients across regions of the United States." J anim sci 77(suppl.2): 90-100.
Nutrient balance in the ecosystem involves profitability of the agricultural enterprise and commitments to resource management to maintain quality of air, water, and land resources. Phosphorus and N are the two nutrients of major concern, and they behave differently in soils. Most P adheres strongly to soil particles and moves laterally with the soil during erosion processes, but with high concentrations more P remains in soluble forms and moves in the water fraction. Most N is soluble and moves laterally or downward with soil water. Soil scientists and agronomists have researched soil processes, plant nutrition, cropping systems, and water quality issues mainly on a field and farm level, but now the movement is to management and regulation of nonpoint problems on a watershed basis as proposed in the Clean Water Action Plan. The plan recognizes the vast diversity of soil parent materials and climates among geographic areas, even among and within watersheds, that determine crop adaptation and cropping systems, the role of states in regulatory processes, and the need for local citizens to have operational involvement. This process insures that nutrient management guidelines will be more site-specific and solutions can be focused on the direct problem. Directed efforts will be needed to educate local citizens, landowners, and caretakers of agricultural enterprises, and regulatory agencies. Several factors, including economic and social incentives for implementation must be considered along with the technologies available. The solutions are multidisciplinary, will require long-term research to accommodate climate variation, and should be associated with a strong commitment to education. Public.

Nelson, M. R., T. V. Orum, et al. (1999). "Applications of geographic information systems and geostatistics in plant disease epidemiology and management." Plant dis 83(4): 308-319.

Pande, S. (1999). GIS analysis of cropping systems. Ithaca, N.Y., Cornell University ; Patancheru, Andhra Pradesh, India : ICRISAT, 1999. v, 158 p. : col. ill., col. maps.

Pelletier, G. and S. K. Upadhyaya (1999). "Development of a tomato load/yield monitor." Comput electron agric 23(2): 103-117.
The objective of this study was to develop a load/ yield monitor for mounting on a processing tomato harvester. A continuous mass flow-type yield-sensing device equipped with load cells and a vibration-resistant angle transducer along with a differential global positioning system (DGPS) was developed to collect spatially variable yield data in real-time. Both analog and digital signal processing were employed to maximise the accuracy of data acquisition. The yield monitoring system was calibrated, validated, and tested during the 1997 harvesting season. The coefficient of determination, r(2), between the actual fruit weight and the yield monitor prediction was 0.997. The system was then used to measure yield variability and produce yield maps. There were significant spatial variations in processing tomato yield. The lowest 20% yielding area within a field produced less than half the tomatoes compared to the highest 20% yielding area within the same field.

Pierce, F. J. and P. Nowak (1999). "Aspects of precision agriculture." Adv agron 67: 1-85.

Plant, R. E., A. Mermer, et al. (1999). "Factors underlying grain yield spatial variability in three irrigated wheat fields." Trans ASAE 42(5): 1187-1202.

Pozdnyakova, L. and R. Zhang (1999). "Geostatistical analyses of soil salinity in a large field." Precis agric 1(2): 153-165.
Estimating spatial variability of soil salinity is an important issue in precision agriculture. Geostatistical methods provide a means to study the heterogeneous nature of spatial distributions of soil salinity. In this study, geostatistical methods, kriging and cokriging, were applied to estimate sodium adsorption ratio (SAR) in a 3375 ha agricultural field. In cokriging, more easily measured data of electrical conductivity (EC) were incorporated to improve the estimation of SAR. The estimated spatial distributions of SAR using the geostatistical methods with various reduced data sets were compared with the extensive salinity measurements in the large field. The results suggest that sampling cost can be dramatically reduced and estimation can be significantly improved using cokriging. Compared with the kriging results using total SAR data, cokriging with reduced data sets of SAR improves the estimations greatly by reducing mean squared error and kriging variance up to 70% and increasing correlation of estimates and measurements about 60%. The sampling costs for SAR estimation can be reduced approximately by 80% using extensive EC data together with a small portion of SAR data in cokriging.

Rejesus, R. M. and R. H. Hornbaker (1999). "Economic and environmental evaluation of alternative pollution-reducing nitrogen management practices in central Illinois." Agric ecosyst environ 75(1/2): 41-53.
Nitrogen fertilizer application from production agriculture is likely the largest contributor to non-point source nitrate pollution in the United States. This type of pollution from the agricultural sector is an important policy issue because it may cause serious environmental and health risks to society. There have been studies that examined the different effects of nitrogen timing and rate practices, but none has yet compared the economic and environmental effects of these practices to site-specific management (SSM) precision technology. This paper examines the economic and environmental impacts of alternative nitrogen management practices, including SSM, within the Lake Decatur watershed of central Illinois. Thus, this study provides evidence on how different nitrogen management practices perform in terms of their effect on water quality and profitability. Data for the analysis were derived from the Environmental Policy Integrated Climate (EPIC) agronomic simulation model due to unavailability of actual on-site data. The analysis revealed that SSM of nitrogen fertilizer has great potential in reducing the mean and variability of nitrate pollution in the watershed while improving profitability of producers, relative to the current practice in the watershed. The management practice where fertilizer is applied during the spring at 140 kg ha-1 provides reduction in mean and variability of nitrate pollution comparable to that of SSM. However, SSM technology substantially reduces the variability of net returns compared to the other management practices analyzed. Hence, SSM of nitrogen fertilizer has the potential to reduce nitrate pollution while reducing economic variability and maintaining.

Robert, P. C. (1999). "Precision agriculture: an information revolution in agriculture."

Robert, P. C., R. H. Rust, et al. (1999). Proceedings of the Fourth International Conference on Precision Agriculture, 19-22 July 1998, St. Paul, Minnesota. Madison, Wis., American Society of Agronomy : Crop Science Society of America : Soil Science Society of America, c1999. 2 v. (xxvii, 1938 p.) : ill., maps (some col.).

Schloss, A. L., D. W. Kicklighter, et al. (1999). "Comparing global models of terrestrial net primary productivity (NPP): comparison of NPP to climate and the Normalized Difference Vegetation Index (NDVI)." Glob chang biol 5(suppl.1): 25-34.

Schrock, M. D., D. L. Oard, et al. (1999). "A diaphragm impact sensor for measuring combine grain flow." Appl eng agric 15(6): 639-642.

Seiler, R. L., J. P. Skorupa, et al. (1999). Areas susceptible to irrigation-induced selenium contamination of water and biota in the western United States by Ralph L. Seiler, Joseph P. Skorupa, and Lorri A. Peltz. Carson City, Nev., U.S. Dept. of the Interior ; [Washington, D.C.] : U.S. G.P.O., 1999. iv, 36 p. : col. ill., col. maps.

Slaughter, D. C., P. Chen, et al. (1999). "Vision guided precision cultivation." Precis agric 1(2): 199-216.
A color machine vision based automatic guidance system was developed for precision guidance of an agricultural cultivator. The guidance system was designed to operate in weedy row crop fields at the time of first cultivation. The performance of the system varied from an RMS guidance error of 7 mm under low weed loads to 12 mm under high weed loads and was capable of operating at travel speeds up to 16 km/h.

Sogaard, H. T. (1999). "Evaluation of the accuracy of a laser optic position determination system." J agric eng res 74(3): 275-280.
The positioning accuracy of a laser optic position determination system (PDS) was investigated by mounting it on an agricultural tractor and a sowing machine. The PDS operates in a local earth fixed, three-dimensional coordinate system and estimates both position coordinates and attitude angles of the vehicle in three dimensions. Two experiments were carried out: a precision experiment where the tractor made a furrow in the ground with a stiff tine and a sowing experiment where rows of wheat were sown with a conventional sowing machine. During the experiments, the PDS estimated the position of the tractor and the sowing machine, respectively. These position estimates were then used for estimation of the positions of points in the furrow and the wheat rows. Measurements of the precise location of the furrow and the wheat rows were performed using stationary global positioning system (GPS). The PDS estimates and the GPS measurements were compared to assess the accuracy of the PDS. From the results it appears that the standard deviation of the cross track position error is 3.2 cm in the precision experiment and 3.5 cm in the sowing experiment.

Sonka, S. T., D. A. Lins, et al. (1999). "Production agriculture as a knowledge creating system." Int food agribus manag rev 2(2): 165-178.

Stein, A. and F. W. T. Penning de Vries (1999). Data and models in action : methodological issues in production ecology. Dordrecht ; Boston, Kluwer Academic Publishers, c1999. 184 p. : ill., map.

Steward, B. L. and L. F. Tian (1999). "Machine-vision weed density estimation for real-time, outdoor lighting conditions." Trans ASAE 42(6): 1897-1909.
A system to estimate the weed density between two rows of soybeans was developed. An environmentally adaptive segmentation algorithm (EASA) was used to segment the plants from the background of the image. The effect of two image data transformations on the segmentation performance of the EASA was investigated, and the RGB-IV1V2 transformation resulted in significantly higher quality segmentation results based on morphological opening and closing pixel loss over the RGB-rgb transformation. An adaptive scanning algorithm (ASA) was developed and used to automatically detect crop inter-row edges and to estimate the number of weeds in the inter-row area. Two sets of images were acquired under sunny and overcast sky conditions. The ASA-detected crop row edge positions were significantly correlated with the manually detected crop row positions, with the distribution skewed towards positions internal to the row. ASA weed density estimates were highly correlated with manual weed counts for both lighting conditions. However, when a limited range of the data was considered, much lower correlations resulted, revealing a loss of spatial color resolution due to the transmission of the video signal. The mean execution time of the ASA was 0.038 s for 0.91 m (3 ft) long inter-row regions showing that the algorithm met the real-time constraints necessary to be used as a sensing system for a variable-rate herbicide applicator.

Stombaugh, T. S., E. R. Benson, et al. (1999). "Guidance control of agricultural vehicles at high field speeds." Trans ASAE 42(2): 537-544.
The main objective of this study was to develop an automated agricultural vehicle guidance system capable of controlling the vehicle during high-speed agricultural field operations. The posture sensor used in the study was a kinematic differential Global Positioning System (GPS) receiver. Experimental frequency response tests were used to develop models of steering equipment and vehicle dynamics. Classical feedback control was developed based on these models. Guidance controller effectiveness was evaluated with experimental step response tests. Frequency response tests of vehicle dynamics showed that the transfer junction relating vehicle lateral deviation to steering angle was a double integrator. The dynamics of the automatic steering were within the same frequency range as desired vehicle dynamics. Guidance controller design had to compensate for both vehicle and steering equipment dynamics. When the GPS sensor was mounted above the front axle of the vehicle, guidance control to within 16 cm of the desired path was demonstrated at speeds up to 6.8 m/s. Moving the sensor rearward to a more practical location added phase lag to the system, and guidance control was less effective.

Szilagyi, J. and M. B. Parlange (1999). "Defining watershed-scale evaporation using a normalized difference vegetation index." J Am Water Resour Assoc 35(5): 1245-1255.
Monthly composites of the Normalized Difference Vegetation Indices (NDVI), derived from the National Oceanic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR), were transformed linearly into monthly evaporation rates and compared with detailed hydrologic-model simulation results for five watersheds across the United States. Model-simulated monthly evaporation values showed high correlations (mean R(2) = .77) with NDVI-derived evaporation estimates. These latter estimates, used in a classical water balance model, resulted in equally accurate simulations of monthly runoff than when the model was run to estimate monthly evaporation via soil moisture accounting. Comparison of NDVI-derived evaporation estimates with pan data showed promise for transforming NDVI values into evaporation estimates under both wet and water-limiting conditions without resorting to the application of any kind of calibrated hydrologic models.

Thomas, D. L., C. D. Perry, et al. (1999). "Development and implementation of a load cell yield monitor for peanut." Appl eng agric 15(3): 211-216.
A yield monitoring system, which uses load cells mounted below the basket, was developed for application to existing and new peanut combines. A tank weighing assembly (free movement in both lateral directions) mount was used with double ended shear beam load cells in a 90 degrees configuration to create the most flexibility with least opportunity for binding at the mounts. Slopes less than 2 degrees did not appreciably affect the load cell response. Moving average and regression methods were used to translate the continuous loading of the basket to incremental loading rates. The system was capable of reproducing input loading rates to within a 1.5 to 7.3% error over an assumed ground area of 20 m(2) to 10 m(2) (220 ft(2) to 110 ft(2)), respectively (under static operating conditions). The larger the area (number of values) included in the average, the smaller the error, but the less sensitivity to changing yield conditions. Additional integration with position signals, improved filtering, and some method of adjusting for pod moisture and trash are necessary to fully develop the system for commercial application.

Thomasson, J. A., D. A. Pennington, et al. (1999). "Cotton mass flow measurement: experiments with two optical devices." Appl eng agric 15(1): 11-17.
Mass flow measurement of pneumatically conveyed cotton is important in at least two processes: yield monitoring during harvesting, and input and output determinations at various stages of ginning. In this work, two experimental devices were constructed and tested for measuring the flow of pneumatically conveyed cotton. One (device A) was used to collect data in the seed-cotton unloading duct of a gin, a cotton picker duct, and a lint-cleaner-waste duct. The other (device B) was used to collect data in the seed-cotton unloading duct of a gin and a lint-cleaner-waste duct. Tests were conducted in which known amounts of cotton were conveyed through the duct over a known time period, making it possible to calculate the average actual material flow rate. The average output of each device during the test runs was also calculated. Actual flow rate was compared to measured flow rate with linear regression. For seed cotton in the unloading duct, both devices performed well. For seed cotton in the picker chute, device A performed well, but device B was not tested. For waste in the lint-cleaner-waste duct, device A performed well and better than device B. In most cases, the correlation between sensor output and cotton mass flow was strong. Both devices look promising for application in appropriate locations in a cotton picker or gin.

Tredaway, J. A., R. M. Hayes, et al. (1999). "A comparison of conventional to site specific weed management technology." Proc S Weed Sci Soc 52: 51.

Trenholm, L. E., R. N. Carrow, et al. (1999). "Relationship of multispectral radiometry data to qualitative data in turfgrass research." Crop sci 39(3): 763-769.
Multispectral radiometry provides a method for assessing plant light reflectance in the visible and near-infrared ranges. Reflectance of narrow wavelength ranges as well as ratios of different ranges have been highly correlated with absorbency of photosynthetically active radiation, leaf area index (LAI), and plant response to stresses. The objectives of this research were to determine if data obtained by multispectral radiometry might accurately correlate with qualitative data (used as rapid estimates of color, density, and uniformity) typically used in turfgrass research. Furthermore, it was our objective to determine whether multispectral radiometry could discriminate between stressed and nonstressed turfgrass plots. This research was conducted in two consecutive trials during 1997 on seven seashore paspalum (Paspalum vaginatum Swartz) ecotypes and three hybrid bermudagrass (Cynodon dactylon L. x C. transvaalensis Burtt-Davy) cultivars established on a native Appling (clayey, kaolinitic, thermic Typic Kanhapludult) soil at the University of Georgia Experiment Station in Griffin, GA. Reflectance at 661 and 813 nm, as well as the ratios normalized difference vegetation index (NDVI, computed as R(935) - R(661)/R(935) + R(661)), infrared/red (IR/R) (LAI, computed as R(935)/R(661)), Stress1 (R(706)/R(760)), and Stress2 (R(706)/R(813)) were highly correlated with visual turf quality, shoot density, and shoot tissue injury (STI) ratings, but not with shoot clipping growth. Regression analysis also indicated very strong associations with each of these qualitative variables, but not with shoot growth data. Additionally, spectral measurements at all wavelengths except 559 and 706 nm were able.

Wadsworth, R. and J. Treweek (1999). GIS for ecology : an introduction. Harlow, Addison Wesley Longman, 1999. xiii, 184 p., [4] p. of plates : ill. (some col.), maps.

Wagner, W. C. (1999). "Sustainable agriculture: how to sustain a production system in a changing environment." Int j parasitol 29(1): 1-5.
During the past 1-15 years, sustainable agriculture has progressed from a focus primarily on a low-input, organic farming approach with a major emphasis on small fruit or vegetable production farms, often described as Low Input Sustainable Agriculture, to the current situation where sustainability is an important part of mainstream animal and plant production units. The US Department of Agriculture programmes cover a broad range of activities, including conserving the natural resource base, enhancing environmental quality, and sustaining productivity of the nations farms. The use of Geographic Information Systems technology to direct application of fertilisers, pesticides, and herbicides is one example of a rapidly emerging technology that can reduce use of external inputs, protect the agricultural environment, and improve economic returns, This Geographic Information Systems technology also is being used to localise animal pest and disease problems, assist in regulatory or control measures, and identify high risk areas that might need different management systems or should be avoided as sites for animal production. Use of intensive grazing systems also has increased markedly over the past 5-6 years. These systems will allow longer grazing seasons in southern parts of the USA, provide more efficient use of the forages being produced and reduce labour costs in the typical dairy operation. Major animal and plant production agriculture-oriented programmes at the US Department of Agriculture focus on integrated production systems, use of Integrated Pest Management techniques, and development of alternative methods to manage pests and diseases that reduce or avoid the.

Wahlstrom, E., K. Loague, et al. (1999). "Hydrologic response: Kaho'olawe, Hawaii." J environ qual 28(2): 481-492.
Kaho'olawe, the eighth largest island in the Hawaiian chain, has experienced major surface erosion during the last century due to overgrazing and military activity. In this paper we report the results from a series of physically-based numerical simulations of hydrologic response, to large rainfall events, that were performed for Kaho'olawe. An event-based rainfall-runoff and erosion model (i.e., KINEROS) was applied, in a geographic information system (GIS) framework, to make quantitative and distributed estimates of infiltration, Horton overland flow generation, and erosion. A digital elevation model (DEM) was employed to delineate individual catchments across the island, and define areas of uniform slope within each catchment. A Landsat MSS scene of Kaho'olawe was used to classify the island into three distinct landcover categories via the normalized difference vegetation index (NDVI). The landcover categories were then used to further approximate the spatial pattern of near-surface soil hydraulic properties across the island. Distributed estimates of saturated hydraulic conductivity and sorptivity were obtained by ordinary kriging of 135 field measurements from the island. Sensitivity analysis was performed to characterize what impact the uncertainty in soil-hydraulic property and rainfall data had on simulated runoff. Horton overland flow and the related transport limited erosion were shown to be highly variable. The introduction of vegetation to denuded areas on Kaho'olawe was found to significantly reduce erosion.

Wallace, T. P. (1999). "Small plot evaluation of an electro-optical cotton yield monitor." Comput electron agric 23(1): 1-8.
The application of precision agriculture to cotton (Gossypium hirsutum L.) production has been limited due to the lack of a suitable yield monitor. Cotton yield monitors under research have utilized load cells, sound sensors and electro-optical devices to measure seedcotton yield. A commercial electro-optical cotton yield sensor was introduced to the cotton industry in 1997 by the Zycom Corporation, Bedford, MA. The purpose of this study was to evaluate the precision of this new yield monitor on small research plots. Cotton research plots were harvested and monitor values recorded from a single harvesting head. Seedcotton was saved from each plot and weighed for comparison with yield monitor values. Monitor values were compared to cumulative plot weights. A total of 226.8 kg of seedcotton was harvested from 72 plots. A significant linear relationship (r(2) = 0.99) was observed between monitor values and observed plot weights. This yield monitor looked very promising for estimating cotton yields and suggests that this technology may allow for the application of precision agriculture to cotton production.

Wheeler, T. A., H. W. Kaufman, et al. (1999). "Comparison of variable and single-rate applications of aldicarb on cotton yield in fields infested with Meloidogyne incognita." J nematol 31(4, suppl.): 700-708.
Variable-rate applications of the nematicide aldicarb were compared to producer standard rates in eight field tests over 3 years. Test areas (308 to 1,015 m long) were divided into eight or five blocks. Each block contained two plots with a variable-rate treatment (VRT) of aldicarb and a producer standard treatment (PST) of aldicarb. Each VRT plot was divided into three subunits and intensively sampled for Meloidogyne incognita in either the fall or spring before planting. Rates of aldicarb were assigned to each subunit for VRT based on M. incognita population density. In three of the eight tests, VRT resulted in either higher yield or similar yields, but less nematicide applied. In two tests there were no differences between PST and VRT in yields or average rates of aldicarb applied. In three tests, VRT used more aldicarb (>0.17 kg a.i./ha difference) than PST and yields were not significantly different between treatments. In two of the cases where VRT was superior to PST, the producer's rate of aldicarb was judged to be either too low or too high for the average M. incognita density present in the field. In all three cases where PST was superior to VRT, perennial weeds were an important factor also limiting yield. Variable-rate application of aldicarb did not consistently provide for higher yields or lower nematicide usage than standard application rates.

Whitney, J. D., W. M. Miller, et al. (1999). "Precision farming applications in Florida citrus." Appl eng agric 15(5): 399-403.
A cooperative effort between researchers, manufacturers, and growers has been investigating precision farming applications in Florida citrus. Citrus yields, based on the location of volume-based containers, were mapped using a conventional fruit-loading truck, manual harvesters (> 99% of Florida citrus is manually harvested), and GIS/GPS components. These maps were overlaid on geo-referenced aerial photographs of the tree canopies. Two fruit weighing systems were mounted on a fruit-loading truck and integrated with the GIS/GPS components to investigate mapping weight-based yields. Results to date indicate the truck-mounted weighing systems were within 1 to 6% of certified scale weights on 20 t loads of fruit. Electronically recording harvester identity is being integrated with yield mapping to make the entire system more reliable and attractive to harvesters and growers.

Wild, K. and H. Auernhammer (1999). "A weighing system for local yield monitoring of forage crops in round balers." Comput electron agric 23(2): 119-132.
Precision farming requires yield maps of all harvested crops. In order to monitor the yield of forage crops a round baler has been equipped with a weighing system. It was based on a load cell in the drawbar coupling and strain gauges in the axle. Tests were first carried out in static mode; the weights of bales could be determined with errors of less than 1%. Afterwards the suitability of the system for weighing on-the-move was examined. With signal smoothing methods spurious oscillation in the signals could be eliminated. Further investigations are necessary for reducing the remaining errors of up to 10%.

Yu, M., E. Segarra, et al. (1999). "Spatial utilization of phosphorus: implications for precision agriculture practices." Proc Beltwide Cotton Conf 1: 299-302.

Yule, I. J., G. Kohnen, et al. (1999). "A tractor performance monitor with DGPS capability." Comput electron agric 23(2): 155-174.
A data acquisition system was developed to monitor in-field performance of an agricultural tractor. Transducers were mounted to measure operational parameters such as the engine, wheel and ground speed with further devices to measure fuel consumption and field slope. The system also measured, displayed and recorded the forces acting on the three point linkage through a dynamometer system. The force measurement was effected through the lower links and top link, combining with angular position to give the total horizontal and vertical components of the forces acting on the tractor. The signals from the transducers were recorded and displayed on-line through Signal Centre Professional software. Thus, the operator was continually provided with useful information regarding the tractor's performance. In combination with a real time DGPS link, each parameter was attributed to a geographical location and a number of performance parameters were subsequently mapped. Results from field work indicate that significant savings can be made through having appropriate information that allows machine set up to be improved. In this study, a saving of 4.70 pounds per ha(-1) was demonstrated while using a tined cultivator in stubble.

Zuydam, R. P. v. (1999). "A driver's steering aid for an agricultural implement, based on an electronic map and Real Time Kinematic DGPS." Comput electron agric 24(3): 153-163.
A co-ordinate system was introduced to make it possible to describe, in a simple but fast way, the intended route that an agricultural implement should follow in the open field. The co-ordinate system was also used as a reference to compare the actual position of the implement with its intended path, and to calculate lateral position errors of the implement. To measure the actual position of the implement, Real Time Kinematic DGPS was used. The calculated error was used to control a correction device that moved the implement to its predetermined path, within a control band of +/- 20 cm, thereby providing a steering aid for the driver. Field tests with a full-size tractor that followed a winding guide rail with +/- 12 cm lateral undulations, while the implement was programmed to cover a straight track, showed an average error of 2 cm, when moving at a speed of 5.2 km/h. In a second series of experiments, a small four-wheeled cart was pushed along a concrete road, being swung left and right at random. An electrical side-shift actuator was used to write a chalk line on the road that represented the actual path of the imaginary implement. The straight, programmed path to be followed by the implement was represented by a permanent line on the road surface, to be compared with the line of chalk. These tests showed an average error of 1 cm at an average speed of 3.6 km h.

(2000). Proceedings of the 5th International Conference on Precision Agriculture and other resource management : July 16-19, 2000, Bloomington, MN USA. Madison, WI, Precision Agriculture Center, University of Minnesota, ASA-CSSA-SSSA, c2000. 1 CD-ROM : col.

(2000). Proceedings of the Second International Conference Geospatial Information in Agriculture and Forestry : 10-12 January 2000, Lake Buena Vista, Florida, USA. Ann Arbor, MI, ERIM International, c2000. 2 v. : ill. (some col.), maps.

Adams, M. L., S. Cook, et al. (2000). "Using yield maps and intensive soil sampling to improve nitrogen fertiliser recommendations from a deterministic model in the Western Australian wheatbelt." Aust j exp agric 40(7): 959-968.

Al Mahasneh, M. A. and T. S. Colvin (2000). "Verification of yield monitor performance for on-the-go measurement of yield with an in-board electronic scale." Trans ASAE 43(4): 801-807.
A commercial combine equipped with a yield monitor and Global Positioning System (DGPS) was constructed to include a weighing system in the clean grain tank. The scale was able to output its current readings two times per second to a data-logger. The reading from the yield monitor and the scale could be matched to check the accuracy of the yield monitor summary as well as the individual (1 s) readings. Harvest data from fields of corn and oats were collected using this system. Data from both the scale and yield monitor were analyzed to verify the accuracy of the yield monitor. The scale was verified to be accurate by calibration. Results showed that the yield monitor has two data processing streams; one gives the individuals weights (1 s interval weights) and the other gives the summary weights (total load weights). The results showed that these two streams are slightly different. Further analysis was conducted to understand these differences. The results showed an increase in the yield monitor accuracy with the harvest strip length. Data collected in 1997 were more accurate than data collected in 1996. It was concluded that improvement was primarily due to the updated yield monitor system (ver. 6.02 CJC).

Alphen, B. J. v. and J. J. Stoorvogel (2000). "A functional approach to soil characterization in support of precision agriculture." Soil Sci Soc Am j 64(5): 1706-1713.
Managing soil variability is an integral aspect of precision agriculture (PA). Existing soil databases, however, are found to match few of the requirements for PA. The nature of these requirements and their implications for soil information need to be further explored. Ongoing developments towards a decision support system (DSS) for PA in the Netherlands have shed some light on this issue. Two soil related DSS-components are presented: (i) the construction of a soil database at the farm level and (ii) the delineation of soil functional units at the field level. Developed methods were tested in a case study for two arable fields located on Dutch marine clay soils. Basic soil data were collected in a 1:5000 soil survey and supplemented with secondary data derived through pedotransfer functions. Soil characterization focused on functional properties describing soil-specific characteristics in terms of water regimes and nutrient dynamics. Four properties were considered: (i) water stress, (ii) N-stress, (iii) N-leaching and (iv) residual N-content at harvest. These were quantified for individual soil profiles using a mechanistic-deterministic simulation model. Sensitivity to water stress was evaluated for a dry year (1989), other properties were quantified for a wet year (1987). Based on functional similarity, the soil profiles were grouped into functional classes using a fuzzy c-means classifier. Standard interpolation techniques and a boundary detection algorithm subsequently identified soil functional units in each field. Analysis of variance revealed that >65% of the spatial variation could thus be accounted for. This confirmed that (i) the proposed classification procedure was efficient and.

Aparicio, N., D. Villegas, et al. (2000). "Spectral vegetation indices as nondestructive tools for determining durum wheat yield." Agron j 92(1): 83-91.
Remote sensing measurements may be a useful tool for quantifying crop development and yield. Our objective was to study the potential of using spectral reflectance indices to provide accurate and nondestructive estimates of physiological traits determining yield in durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.]. Twenty-five genotypes were grown under rainfed and irrigated conditions in northeastern Spain. Reflectance from the vegetation at different growth stages was measured and the following spectral indices calculated: simple ratio (SR), normalized difference vegetation index (NDVI), and photochemical reflectance index (PRI). Crop dry mass (CDM), leaf area index (LAI), and green area index (GAI) were measured. All the indices and grain yield were greater under irrigated than rainfed conditions. LAI was the crop growth trait that most closely correlated with the spectral reflectance indices, with SR and PRI being the best and the worst indices, respectively, for the assessment of crop growth and yield. In rainfed conditions, the spectral reflectance indices measured at any crop stage were positively correlated (P < 0.05) with LAI and yield. Under irrigation, correlations were only significant during the second half of the grain filling. The integration of either NDVI, SR, or PRI from heading to maturity explained 52, 59, and 39% of the variability in yield within genotypes in rainfed conditions and 39, 28, and 26% under irrigation. Our results suggest that for durum wheat, the usefulness of the SR and NDVI for calculating green area and grain yield is limited to LAI values < 3.

Arslan, S., F. Inanc, et al. (2000). "Grain flow measurements with X-ray techniques." Comput electron agric 26(1): 65-80.

Bailey, J. S., A. Higgins, et al. (2000). "Empirical models for predicting the dry matter yield of grass silage swards using plant tissue analyses." Precis agric 2(2): 131-145.

Bakhsh, A., T. S. Colvin, et al. (2000). "Using soil attributes and GIS for interpretation of spatial variability in yield." Trans ASAE 43(4): 819-828.
Precision farming application requires better understanding of variability in yield patterns in order to determine the cause-effect relationships. This field study was conducted to investigate the relationship between soil attributes and corn (Zea mays L.)-soybean (Glycine max L.) yield variability using four years (1995-98) yield data from a 22-ha field located in central Iowa. Corn was grown in this field during 1995, 1996, and 1998, and soybean was grown in 1997. Yield data were collected on nine east-west transects, consisting of 25-yield blocks per transect. To compare yield variability among crops and years, yield data were normalized based on N-fertilizer treatments. The soil attributes of bulk density, cone index, organic matter, aggregate uniformity coefficient, and plasticity index were determined from data collected at 42 soil sampling sites in the field. Correlation and stepwise regression analyses over all soil types in the field revealed that Tilth Index, based upon soil attributes, did not show a significant relationship with the yield data for any year and may need modifications. The regression analysis showed a significant relationship of soil attributes to yield data for areas of the field with Harps and Ottosen soils. From a geographic information system (GIS) analysis performed with ARC/INFO, it was concluded that yield may be influenced partly by management practices and partly by topography for Okoboji and Ottosen soils. Map overlay analysis showed that areas of lower yield for corn, at higher elevation, in the vicinity of Ottosen and Okoboji soils were consistent from year to year; whereas, areas of higher yield were variable. From GIS and statistical analyses, it was concluded.

Bakhsh, A., D. B. Jaynes, et al. (2000). "Spatio-temporal analysis of yield variability for a corn-soybean field in Iowa." Trans ASAE 43(1): 31-38.
Spatio-temporal analyses of yield variability are required to delineate areas of stable yield patterns for application of precision farming techniques. Spatial structure and temporal stability patterns were studied using 1995-1997 yield data for a 25-ha field located near Story City, Iowa. Corn was grown during 1995-1996, and soybean in 1997. The yield data were collected on nine east-west transects, consisting of 25 yield blocks per transect. The two components of yield variability, i.e., large-scale variation (trend) and small-scale variation, were studied using median polishing technique and variography, respectively. The trend surface, obtained from median polishing, accounted for the large-scale deterministic structure induced by treatments and landscape effects. After removal of trend from yield data, the resulting yield residuals were used to analyze the small-scale stochastic variability using variogram analysis showed strong spatial structure for the yield residuals. The spatial correlation lengths were found to vary from about 40 m for corn to about 90 m for soybean. The range parameter of the variograms showed a significant correlation coefficient of -0.95 with the cumulative growing season rainfall. The total variance of 1995 corn yield was partitioned as 56% trend, 37% small-scale stochastic structure, and 7% as an interaction of both. Yield variance of 1996 corn was about 80% trend and 20% small-scale stochastic structure. Contrary to corn years, the total yield variance for soybean in 1997 was partitioned as about 25% trend and about 75% small-scale stochastic structure. The significant negative correlation of range with rainfall shows that small-scale variability may be.

Barr, A., M. Bennett, et al. (2000). "Geographic information systems show impact of field placement on sh2 sweet corn stand establishment." HortTechnology 10(2): 341-350.
The objective of this study was to ascertain if stand establishment of sh2 sweet corn (Zea mays L.) would benefit from variable planting depths determined by the use of geographic information systems (GIS). Spring and fall research plots were established in a field [80 x 20 m (262 x 66 ft)] containing Crosby silt loam and Kokomo silty day loam soil series in Columbus, Ohio. Three sh2 sweet corn cultivars (Starship, Skyline, and Confection) were planted at three depths on the two soil types in the fall study, with an additional transition soil added in the spring. Emergence counts as well as soil moisture and temperature were monitored. In the spring, sites were also sampled for nutrient levels and soil compaction. Significant variability was found within the field with respect to soil moisture, temperature, nutrient levels, and compaction. Seedling emergence fluctuated with average soil moisture increasing in blocks with up to 24% moisture and then leveling off. Daily minimum soil temperatures impacted stand establishment. Although heat units accumulated faster on the Crosby soil, emergence was slower and less complete on these soil series than on Kokomo soil series. Further investigation determined that although temperatures of the Crosby soil were 3 to 4.5 degrees C (5.4 to 8.1 degrees F) warmer during the day than the Kokomo soil, temperatures on the Crosby soil averaged 2 degrees C (3.6 degrees F) cooler at night. Analysis of emergence patterns and field variability was performed on ArcView mapping software. Although 'Skyline' planted at 2 cm (0.8 inches) had the best emergence overall, final stand would have been increased with 'Skyline' planted variably at 2 and 4 cm (1.6 inches). Mapping.

Batte, M. T. (2000). "Factors influencing the profitability of precision farming systems." J soil water conserv 55(1): 12-18.

Birrell, S. J. and J. W. Hummel (2000). "Membrane selection and ISFET configuration evaluation for soil nitrate sensing." Trans ASAE 43(2): 197-206.

Bocchi, S., A. Castrignano, et al. (2000). "Application of factorial kriging for mapping soil variation at field scale." Eur J agron 13(4): 295-308.

Bounoua, L., G. J. Collatz, et al. (2000). "Sensitivity of climate to changes in NDVI." J climate 13(13): 2277-2292.

Bullock, D. S. and D. G. Bullock (2000). "From agronomic research to farm management guidelines: a primer on the economics of information and precision technology." Precis agric 2(1): 71-101.
An ultimate purpose of much agronomic and agricultural economic research is to provide management guidelines (e.g., on application rates of fertilizer, seed, and herbicides) to farmers. Ideally, farm management guidelines or recommendations would be determined by applying sound economic theory to data from agronomic experiments. while information provided by agronomic data about the relationship between crop yields, managed inputs, soil characteristics, and weather variables has always been valuable, we argue in this paper that because such information and precision agriculture technology are economic complements, the advent of precision agriculture technology has made information provided by agronomic experiments now even more valuable than ever. The purpose of this paper is to point out and respond to two practical implications of the complementarity between precision technology and information from agronomic research. The first implication is that because precision technology has made information more valuable, it is also more costly now when agronomists make mistakes in using economic theory to derive incorrect farm management recommendations from the information. Therefore it is more important than ever that agronomists understand some basic economic theory about agricultural production and precision technology. Our response is to provide here an economic primer on precision agriculture and information. We also recommend increased collaboration between agronomists and agricultural economists in precision technology research. The second implication is that, because precision technology has made information more valuable, there is more need than ever for long-term.

Burks, T. F., S. A. Shearer, et al. (2000). "Classification of weed species using color texture features and discriminant analysis." Trans ASAE 43(2): 441-448.

Camp, C. R., E. J. Sadler, et al. (2000). "Variable-rate, digitally controlled metering device." Appl eng agric 16(1): 39-44.

Cassel, D. K., O. Wendroth, et al. (2000). "Assessing spatial variability in an agricultural experiment station field: opportunities arising from spatial dependence." Agron j 92(4): 706-714.

Cho, S. I. and J. H. Lee (2000). "Autonomous speedsprayer using differential global positioning system, genetic algorithm and fuzzy control." J agric eng res 76(2): 111-119.
A fuzzy controller was developed for the autonomous operation of a speedsprayer in an orchard. The autonomous operation with a fuzzy controller was graphically simulated under the real orchard conditions. A differential global positioning system (DGPS) receiver was used to determine the direction of travel and four ultrasonic sensors were used to detect obstacles during operation. The results of the simulation showed that the speedsprayer could be operated autonomously with the fuzzy controller combined with the DGPS receiver and the ultrasonic sensors. The DGPS receiver signal, and the signals from the ultrasonic sensors, were processed in real time. The speedsprayer was modified to be steered by two hydraulic cylinders. The fuzzy controller has two inputs: direction of travel and distance from obstacles. The operating time of the hydraulic cylinders was inferred as output of the fuzzy controller. The results of the field test showed that the speedsprayer could be autonomously operated within 50 cm deviation. The ultrasonic sensors did not contribute to the improvement of guidance performance. The speedsprayer, however, could avoid trees or obstacles in emergency situations with them. According to a computer simulation, performance of the fuzzy controller was improved by 68% using a genetic algorithm. However, according to the field test, performance of the fuzzy controller using the genetic algorithm was not improved much because of tyre slip and response time gap of the hydraulic system.

Clay, D. E., J. Chang, et al. (2000). "Precision farming protocols. Comparison of sampling approaches for precision phosphorus management." Commun soil sci plant anal 31(19/20): 2969-2985.

Comis, D. (2000). "Precise inputs for a cleaner environment." Agric res 48(1): 4-8.

Cook, S. E. and R. G. V. Bramley (2000). "Coping with variability in agricultural production--implications for soil testing and fertiliser management." Commun soil sci plant anal 31(11/14): 1531-1551.
Decisions about fertiliser applications are fraught with uncertainty. Uncertainty about the outcome of an application of fertiliser is caused by unknown or uncontrolled variation about the condition of the soil to which it is applied, its fate, and the demand from the crop. Uncertainty can be eased by providing information which reduces ignorance about the likely outcomes of applying fertiliser, thereby increasing the decision-maker's chances of success. Such information could include analyses of soil and plant tissue, prior information about crop performance, and predictions of climate and prices. This information could be used to improve the rate, location and timing of applications. Precision agriculture technology greatly enhances our ability to acquire and manage more of this information. However, information costs money, which must be traded-off against the greater likelihood of success. This trade-off is very difficult to evaluate, and in practice depends on a range of factors, including the availability of data, current understanding of its meaning and the preferences of the decision-maker. Research in the Western Australia (WA) wheatbelt, suggests that conventional soil testing is of limited value in explaining variability of crop response in the field. Possible reasons for this include the inadequate representation of major sources of variation--in particular water availability, weeds or disease; inaccurate representation of nutrient uptake mechanisms; and errors of calibration over large agro-ecological regions and wide ranges in soil types or properties. We suggest that this situation may be improved somewhat by more sensitive methods which can.

Cordesses, L. (2000). "Combine harvester control using real time kinematic GPS." Precis agric 2(2): 147-161.

Davenport, J. R. and M. J. Hattendorf (2000). "Using site-specific approaches to advance potato management in irrigated systems." HortTechnology 10(3): 452-457.
Potatoes (Solanum tuberosum L.) are grown extensively throughout the Pacific northwestern United States as a high value crop in irrigated rotations with other row crops such as wheat (Triticum aestivum L.) and both field and sweet corn (Zea mays L.). Center pivots are the predominant irrigation systems. Soil texture ranges from coarse sands to finer textured silt loams and silts and can vary within one field, particularly in fields with hilly topography. Site specific management is being evaluated as an approach to help to optimize inputs (water, seed, agricultural chemicals) to maintain or enhance yield and reduce potential negative environmental impacts from these farming systems. Currently, variable rate fertilizer application technology and harvest yield monitoring equipment are commercially available for potato. Variable rate seeding and variable rate irrigation water application technologies are developed but not fully commercialized and variable rate pesticide application equipment is in development. At the Irrigated Agricultural Research and Extension Center in Prosser, Wash., we have a team of research scientists, interested individuals from local industry, and other key organizations (e.g. local conservation districts) who are working together to evaluate different site specific technologies, improve the ability to use available tools, and to improve decision-making ability by conducting research both on farm and in research plots.

DeShazer, J. A. and G. E. Meyer (2000). Biological quality and precision agriculture II : 6-8 November 2000, Boston, USA. Bellingham, Wash., USA, SPIE, c2000. vii, 176 p. : ill.

Dokladalova, M. and W. T. Lanini (2000). "End of the era of uniform herbicide applications." Proc annu Calif Weed Sci Soc(52nd): 189-190.

Douglas, B. W., J. A. MacLeod, et al. (2000). "A method for measuring Prince Edward Island soil quality." Commun soil sci plant anal 31(11/14): 1837-1845.
Prince Edward Island (PEI) has a land area of 575,000 hectares and its landscape is undulating. About half the land is cleared, the other half under natural forest. The long term effect of intensive farming practices on soil health is becoming a matter of concern as it is felt that soil quality may deteriorate through continuous agrichemical inputs and loss of productive topsoil through erosion. This study was established to: set up a process to measure soil quality, establish soil quality indicators, measure soil quality on an on-going basis and report results to the public. The sampling locations were selected on a 4 km x 4 km grid across PEI. A total of 232 agricultural sampling locations were selected and located by GPS (Global Positioning System). A cluster of up to five samples was taken at each location, depending on land use. One sample will be taken at the selected GPS coordinates and the other four, 100 metres due south, north, west and east respectively. In the 232 sampling locations selected, the actual number of samples taken will be 796. One third of the sampling locations are being sampled each year, starting in 1998. Three groups of parameters are being measured: Physical Parameters (depth of A and B horizons soil type, length and degree of slope, position of sample on slope, crops grown, crop rotation and type of tillage), Chemical Parameters (Organic Matter, Total Carbon, pH, Phosphorus, Potassium, Calcium, Magnesium, Boron, Zinc, Sulfur, Manganese, Iron, Sodium, CEC, and Base Saturation), Microbial Parameters (microscopic observation, enzyme assays). The analyses of the collected data focuses on determining the existence of statistically significant.

Earl, R., G. Thomas, et al. (2000). "The potential role of GIS in autonomous field operations." Comput electron agric 25(1/2): 107-120.
Two issues of increasing importance in agriculture are the targeted approach to managing field operations, or precision farming, and the development of automated guidance systems. The viability of both of these approaches has been increased by recent technological developments in positioning, sensing and control systems. These separate technologies appear to provide the necessary tools for the adoption of spatially varying crop management strategies, undertaken by autonomous guidance. However, the latter in particular requires a high level of integration of the data and information flows that provide the foundations for the field operations management process. These data and information flows are becoming increasingly complex due to the increasing use of sensing systems to provide information on the spatial and temporal attributes of fields, both stable and transient, at precisely determined locations. In addition, the application of improved agronomic understanding increasingly requires the combined interpretation of separate field attributes. The data and information that are the basis of the field operations management process are electronically recorded and are position and time related. Consequently it is the technology of Geographic Information Systems (GIS) that provides a basis for combined management and guidance applied to autonomous field operations. This paper provides an overview of the potential role of GIS in this context.

Eberlein, C. V., B. A. King, et al. (2000). "Evaluating an automated irrigation control system for site-specific herbigation." Weed technol 14(1): 182-187.

Ehlert, D. (2000). "Measuring mass flow by bounce plate for yield mapping of potatoes." Precis agric 2(2): 119-130.

El Faki, M. S., N. Zhang, et al. (2000). "Factors affecting color-based weed detection." Trans ASAE 43(4): 1001-1009.
Color differences between weeds and crops have been used to develop an image-based sensor to detect weeds in wheat and soybean fields for post-emergency herbicide spot spray. Several field factors were found to affect the correct-classification rate (CCR) of the sensor. CCR is defined as the ratio between the number of weed-stem pixels correctly classified and the total number of weed-stem pixels in an image. The first factor was soil moisture content. Images of weeds and soil at 10 different moisture contents were analyzed using a statistical method. It was found that, within a large variation range of soil moisture content, the values of relative color indices of soil varied within a sufficiently narrow range, which did not seriously overlap with the range for weed stems. As a result, variations in soil moisture content did not cause significant misclassification between soil and weeds. The second factor was illumination. Images of standard RGB primary-color plates were taken at nine different illumination intensities. The effect of illumination on color indices was found significant. However, the variation ranges of the relative color indices on images of the color plates did not overlap, and the variations of the index values followed noticeable patterns, which could be used in color-index calibration. The third factor studied was spatial resolution. Nine different spatial resolutions of weed images were achieved by taking images at different camera-plant distances. The optimum resolution, at which the CCR was maximized, was found to be about 0.5 mm. The classifier was tested on field images obtained under natural lighting conditions. The classifier.

El Faki, M. S., N. Zhang, et al. (2000). "Weed detection using color machine vision." Trans ASAE 43(6): 1969-1978.
Many weed species have reddish stems, but stems of wheat and soybean are green. These color features were used in this study to establish a simple weed-detection method using a color machine-vision system. This method is more practical than texture- or shape-based methods because of its low sensitivity to canopy overlap, leaf orientation, camera focusing, and wind effect. Four types of relative color indices formed by RGB gray levels were designed. The most effective combinations of these color indices were selected using a statistical method. These combinations were used as the input variables for a statistical classifier based on discriminant analysis (DA) and two artificial neural-network (NN) classifiers. These classifiers were trained and tested using three weed species (Johnsongrass, redroot pigweed, and yellow foxtail) with soybean and three weed species (wild buckwheat, cheat, and field bindweed) with wheat. Preprocessing and postprocessing algorithms were developed to shorten the processing time and to reduce noise. The results showed that the statistical DA classifier was more accurate than the NN classifiers in classification accuracy. The least-square means of the classification rates using the DA classifiers for soybean and wheat were 54.9% and 62.2%, respectively. The misclassification rates for most weed species were below 3%. Because the reddish colors on the stems of some weed species vary as the plants grow, an in-field calibration procedure will be needed to make the classifiers more adaptive to different circumstances.

Fleming, K. L., D. G. Westfall, et al. (2000). "Evaluating farmer defined management zone maps for variable rate fertilizer application." Precis agric 2(2): 201-215.

Gandah, M., A. Stein, et al. (2000). "Dynamics of spatial variability of millet growth and yields at three sites in Niger, West Africa and implications for precision agriculture research." Agric syst 63(2): 123-140.

Groenigen, J. W. v., M. Gandah, et al. (2000). "Soil sampling strategies for precision agriculture research under Sahelian conditions." Soil Sci Soc Am j 64(5): 1674-1680.
The cost of soil samples to characterize field variability is a key problem in precision agriculture. This study was conducted to investigate whether yield maps can be used to optimize soil sampling for characterizing soil variables that determine yield variability. Using an inexpensive, low-tech scoring technique, yield maps of pearl millet [Pennisetum glaucum (L.) Br.] were produced for a zero-input farm in Niger. The soil was classified as a typic Plintustalf. The Spatial Simulated Annealing (SSA) algorithm was used to optimize three sampling schemes. Scheme 1 optimized coverage over the whole area. Scheme 2 covered the whole yield range. Scheme 3 covered the low-producing areas. Yield varied from 0 to 2500 kg ha-1, measured per planting hill. Using correlation coefficients, Scheme 2 found significant correlations between five soil variables and yield. Scheme 1 found only one significant correlation and explained 37% of the variation in yield using multivariate regression of yield on soil variables. Scheme 2 explained 70% of the variation in yield. Differences between Scheme 3 and Scheme 1 proved to be significant for distance to shrubs, relief, soil pH, and cation-exchange capacity (CEC). We concluded that shrubs are the main factor influencing millet yield by means of catching eroded materials and improving soil fertility. The possibilities of planting shrubs to improve soil fertility should be investigated. Variograms of relief and yield suggested that spatial correlation is largely confined to distances of 3 to 5 m. Since Scheme 2 was most effective in establishing soil-yield relationships, we concluded that yield maps can be used to optimize soil sampling.

Gurnell, A. M. and D. R. Montgomery (2000). Hydrological applications of GIS. Chichester ; New York, John Wiley, c2000. vi, 176 p., [15] p. of plates : ill. (some col.), maps (some col.).

Haneklaus, S. and E. Schnug (2000). "Decision-making strategies for the variable-rate application of compound fertilizers." Commun soil sci plant anal 31(11/14): 1863-1873.
The implementation of precision agriculture technologies is probably one of the greatest opportunities of the 21st century to expand the horizons for soil and plant analyses by converting the spatial variability of soil and crop characteristics into a spatially variable input of agro-resources in order to match the local demand in the field. Compound fertilizers have been developed in order to simplify fertilization, but with their use in precision agriculture the following major problems need to be faced: firstly, the spatial variability of optimum fertilizer rates between different nutrients are not correlated and secondly the nutrient ratio is constant during application and may lead to an undesired surplus or deficit in different zones of the field, which again is counter-productive to the aims of precision agriculture. In this paper, different decision-making strategies for variable-rate applications of compound fertilizers are presented which include a balanced fertilizer input over a three-year crop rotation.

Hatfield, J. L. (2000). Precision agriculture and environmental quality : challenges for research and education. [United States], USDA National Resources Conservation Service : USDA Agricultural Research Service, [2000] 18 p.

Jones, D. and E. M. Barnes (2000). "Fuzzy composite programming to combine remote sensing and crop models for decision support in precision crop management." Agric syst 65(3): 137-158.

Karsky, D. and T. Jasumback (2000). Evaluation of the PLGR GPS receiver using WAGE data. Missoula, Mont., U.S. Dept. of Agriculture, Forest Service, Technology & Development Program, [2000] ii, 14 p. : ill.

Kirchmann, H. and G. Thorvaldsson (2000). "Challenging targets for future agriculture." Eur J agron 12(3/4): 145-161.

Kokubun, M., S. Uchida, et al. (2000). GIS applications for agro-environmental issues in developing regions : proceedings of the 6th JIRCAS International Symposium, Tsukuba, 7-8 September 1999. [Tsukuba, Japan], Japan International Research Center for Agricultural Sciences, Ministry of Agriculture, Forestry and Fisheries, 2000. xxii, 224 p. : ill. (some col.), maps (some col.).

Kravchenko, A. N., D. G. Bullock, et al. (2000). "Joint multifractal analysis of crop yield and terrain slope." Agron j 92(6): 1279-1290.
Quantifying the spatial variability of crop yields and yield-affecting factors are important issues in precision agriculture. Topography is frequently one of the most important factors affecting yields, and topographical data are much easier to obtain than time and labor-consuming measurements of soil properties. In this study, yield variability and the relationships between yields and terrain slopes were analyzed using theories of multifractal and joint multifractal measures. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yield data from 1994 to 1998 were collected via yield monitors from a central 6.6 ha section of an agricultural field in eastern Indiana. Slopes were derived from a field terrain map using a GIS. Multifractal analysis of yield and slope maps revealed that both yield and slope distributions were multifractal measures. Hence, joint multifractal analysis was applied to evaluate the effect of slope on crop-yield spatial variability. Joint multifractal analysis facilitated (i) the ability to differentiate between yield distributions corresponding to field locations with high and low slopes, and (ii) the ability to make inferences about slope distributions that affect grain yield the most. Multifractal analysis revealed that during four growing seasons with moderate and dry weather conditions, larger yields were observed at low slope locations while a wide range of yield values was observed at sites with moderate and high slopes. During the wet growing season, lower yields prevailed at locations with low slopes. Joint multifractal theory was useful for the study of yield/topography relationships and was an applicable tool for the analysis of spatially distributed data.

Kravchenko, A. N. and D. G. Bullock (2000). "Correlation of corn and soybean grain yield with topography and soil properties." Agron j 92(1): 75-83.
Analysis of yield variability is an important issue in agricultural research, and topographical land features are among the most important yield-affecting factors. The objective of this study was to determine how useful topographical information can be, alone or together with selected soil properties, for explaining yield variability on a field scale. Yield-topography-soil relationships were analyzed using dense corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yield data collected from 1994 to 1997, a detailed terrain map, and relatively densely sampled soil organic matter (OM) content, cation exchange capacity (CEC), and P and K soil test concentrations from eight fields in central Illinois and eastern Indiana. Soils of the Illinois fields were classified as Haplaquolls and Argiudolls; soils of the Indiana fields were classified as Hapludalfs. Topographical land features used in the study included elevation, measured with survey grid global positioning system (GPS) and land-based laser, and slope, curvature, and flow accumulation, derived from elevation data. Soil properties explained about 30% of yield variability (from 5 to 71% for different fields), with OM content influencing yield the most. The cumulative effect of the topographical features explained about 20% of the yield variability (6-54%). Elevation had the most influence on yield, with higher yields consistently observed at lower landscape positions. Curvature, slope, and flow accumulation significantly affected yield only in certain conditions, such as extreme topographical locations (undrained depressions or eroded hilltops) combined with very high or low precipitation. Soil properties.

Kunavut, J., J. K. Schueller, et al. (2000). "Continuous control of a sprayer pinch valve." Trans ASAE 43(4): 829-837.
An air pinch valve was modified to be continuously variable by the addition of a rigid insert and continuous air pressure regulation. A technique for state-space modeling of the valve's dynamic performance was developed. State feedback control based upon pole placement was unstable due to unmodelled nonlinearities. Experiments indicated that integral closed-loop control produced satisfactory transient and steady-state responses for individual nozzle control. Such valves might be utilized in the spatially variable control of fertilizer or pesticide application common in precision agriculture.

Lamb, D. W. (2000). "The use of qualitative airborne multispectral imaging for managing agricultural crops--a case study in south-eastern Australia." Aust j exp agric 40(5): 725-738.

Lang, N. S., J. Silbernagel, et al. (2000). "Remote image and leaf reflectance analysis to evaluate the impact of environmental stress on grape canopy metabolism." HortTechnology 10(3): 468-474.
Research suggests that blackleaf (a leaf disorder in grape, Vitis labrusca L.) is induced by high levels of ultra violet (UV) radiation and overall light intensity, resulting in color changes (purple-brown-black) for sun-exposed leaves of the outer canopy, and a corresponding >50% reduction in photosynthesis. Metabolic indicators (photosynthesis and leaf water potential), percent blackleaf expression, and full spectrum leaf reflectance were mapped within vineyards using global positioning system (GPS) and digital remotely-sensed images. Each image and data record was stored as an attribute associated with a specific vine location within a geographical information system (GIS). Spatial maps were created from the GIS coverages to graphically present the progression of blackleaf across vineyards throughout the season. Analysis included summary statistics such as minimum, maximum, and variation of green reflectance, within a vineyard by image capture date. Additionally, geostatistics were used to model the degree of similarity between blackleaf values as a function of their spatial location. Remote-image analysis indicated a decrease in percent greenness of about 45% between July and August, which was related to a decrease in photosynthesis and an increase in blackleaf symptom expression within the canopy. Examination of full spectral leaf reflectance indicated differences at specific wavelengths for grape leaves exposed to UV or water-deficit stress. This work suggests that remote-image and leaf spectral reflectance analysis may be a strong tool for monitoring changes in metabolism associated with plant stress.

Lawrence, P. R., B. Gerard, et al. (2000). "Design and testing of a global positioning system-based radiometer for precision mapping of pearl millet total dry matter in the Sahel." Agron j 92(6): 1086-1095.
The nondestructive determination of plant total dry matter (TDM) in the field is greatly preferable to the harvest of entire plots in areas such as the Sahel where small differences in soil properties may cause large differences in crop growth within short distances. Existing equipment to nondestructively determine TDM is either expensive or unreliable. Therefore, two radiometers for measuring reflected red and near-infrared light were designed, mounted on a single wheeled hand cart and attached to a differential Global Positioning System (GPS) to measure georeferenced variations in normalized difference vegetation index (NDVI) in pearl millet fields [Pennisetum glaucum (L.) R. Br.]. The NDVI measurements were then used to determine the distribution of crop TDM. The two versions of the radiometer could (i) send single NDVI measurements to the GPS data logger at distance intervals of 0.03 to 8.53 m set by the user, and (ii) collect NDVI values averaged across 0.5, 1, or 2 m. The average correlation between TDM of pearl millet plants in planting hills and their NDVI values was high (r2 = 0.850) but varied slightly depending on solar irradiance when the instrument was calibrated. There also was a good correlation between NDVI, fractional vegetation cover derived from aerial photographs and millet TDM at harvest. Both versions of the rugged instrument appear to provide a rapid and reliable way of mapping plant growth at the field scale with a high spatial resolution and should therefore be widely tested with different crops and soil types.

Leboeuf, J. (2000). "Practical applications of remote sensing technology--an industry perspective." HortTechnology 10(3): 475-480.
The initial surge of interest in precision agriculture technologies exhibited by innovators and early adopters involved in crop production appears to have crossed over an important threshold. As valuable field experience increases and learning by doing advances, successful applications of management practices are being identified even though few are adequately documented with economic benefits. Access to accurate information pertaining to applications of site-specific management would be expected to motivate more producers to incorporate technology uses with crop production. This next group of producers has been watching technology developments as they preferred to avoid risk and wait for identifiable benefits. Waiting for detailed case studies involving high value fruits and vegetables may be the wrong approach to take. Fierce competition and strict confidentiality are expected in the fresh market industry. Thus, personal experience with technology becomes more relevant to innovative producers than published literature. This is especially true in California where 350 different crops are produced. High resolution imagery from digital aerial and satellite sensors has been used in crop production in California to identify plant stress, direct plant tissue and soil sampling efforts, and provide information for analysis and interpretation of crop growth. Examples of remote sensing imagery that have provided valuable in-season progress reports will be identified. The focus will be on practice, not theory, as seen from an industry perspective.

Lechner, W. and S. Baumann (2000). "Global navigation satellite systems." Comput electron agric 25(1/2): 67-85.
Global positioning systems first became available for private use in 1995. Since the introduction of NAVSTAR-GPS (Navigation System with Time and Ranging-Global Positioning System) and GLONASS (Globaluaya Navigatsionnaya Sputnikovaya Sistema, Global Navigation Satellite System), such systems have quickly become indispensable in a wide range of applications. Above all, GPS is used today by a large user community. Artificial augmentations can be used to improve the performance of the systems in terms of accuracy, availability and integrity. In space-based augmentations, differential correction data, integrity information and additional ranging signals are transmitted from geostationary satellites. In ground-based augmentations, a reference station (based on a geo-referenced position) compares the position solution (calculated by the SatNav System) with the real coordinates. In that case, the correction data is transmitted by a telemetric system to roving receivers near the reference station. Both augmentation techniques are based on the generic satellite navigation systems GPS or GLONASS, and are dependent on the availability of the source system. To overcome the dependency of the civil European user community upon foreign military systems, an initiative to build up an autonomous European Satellite Navigation System with an own-space segment was initiated. Since 1999, the realisation of this project has been on the way, and the employment of the new system, named Galileo, is currently expected in 2008.

Lowenberg DeBoer, J. (2000). "Comment on "Site-specific crop management: adoption patterns and incentives."" Rev agric econ 22(1): 245-250.

Lukina, E. V., W. R. Raun, et al. (2000). "Effect of row spacing, growth stage, and nitrogen rate on spectral irradiance in winter wheat." J plant nutr 23(1): 103-122.
Soil reflectance affects spectral irradiance measurements taken in winter wheat at early stages of growth when percent cover is low. The objective of this study was to determine the critical percent vegetation coverage needed for forage nitrogen (N) uptake calibration with indirect spectral irradiance measurements. Two field experiments were conducted at Tipton and Perkins, OK in October 1996. The effect of row spacing (15.2, 19.0, 25.4, and 30.5 cm) and growth stage (Feekes 4 and 5) under various N fertilizer rates (0, 56, 112, and 168 kg N ha-1) on spectral irradiance measurements from wheat was evaluated. The normalized difference vegetative index (NDVI) was used to characterized wheat canopy irradiance. In general, NDVI decreased with increasing row spacing and increased with N fertilizer rate at Feekes growth stage 4. Row spacing and N rate were independent of each other since no significant interaction was found. High correlation (r=0.81-0.98) was observed between NDVI and vegetation coverage. Percent vegetation coverage was a good predictor of the other dependent variables including forage dry matter and total N uptake, which could indirectly be determined using NDVI. The coefficients of variation (CV's) from NDVI values decreased with increasing vegetation coverage suggesting that less variable NDVI values (CV less than 10%) might be obtained from plots where vegetation coverage exceeds 50%.

Lutticken, R. E. (2000). "Automation and standardisation of site specific soil sampling." Precis agric 2(2): 179-188.

Maidment, D. R. and D. Djokic (2000). Hydrologic and hydraulic modeling support : with geographic information systems. Redlands, Calif., ESRI Press, c2000. ix, 216 p. : ill. (some col.).

Medlin, C. R. and D. R. Shaw (2000). "Economic comparison of broadcast and site-specific herbicide applications in nontransgenic and glyphosate-tolerant Glycine max." Weed sci 48(5): 653-661.
Weed population estimates were collected from four Glycine max fields during the summers of 1997 and 1998. Seedling weed populations were sampled using a regular coordinate system on a grid either 50 by 50, 30 by 30, or 10 by 10 m. MSU-HERB and Mississippi Herbicide Application Decision Support System (HADSS) (yield loss prediction and herbicide recommendation models for G. max) were used to determine the estimated net gain resulting from simulated herbicide applications at each sample location in each field. When necessary, the appropriate data points from the 10- by 10-m grid were removed to form population data sets on grids 20 by 20, 40 by 40, and 80 by 80 m. The objectives of this research were to compare estimated economic returns of site-specific herbicide management and broadcast herbicide management in nontransgenic and glyphosate-tolerant G. max and to evaluate the effects of various weed sampling intensities on estimated economic returns from site-specific herbicide applications. Site-specific herbicide management was the compilation of simulated herbicide treatments giving the highest estimated net gains at each location within each field. Broadcast herbicide management was the simulated broadcast application giving the highest estimated net gain for each field. Sampling costs and the unattainable site-specific application costs were not included in the estimated net gain calculations. In nontransgenic G. max production, the estimated net gain for treating the four fields with site-specific technology was $104.76 ha-1 higher than when using the optimum broadcast herbicide. In glyphosate-tolerant G. max production, the average estimated net gain for.

Moudon, A. V. and M. H. Hubner (2000). Monitoring land supply with geographic information systems : theory, practice, and parcel-based approaches. New York ; Chichester, Wiley, c2000. xii, 335 p. : ill., maps.

Mowrer, H. T. and R. G. Congalton (2000). Quantifying spatial uncertainty in natural resources : theory and applications for GIS and remote sensing. Chelsea, Mich., Ann Arbor Press, c2000. xxiv, 244 p., [8] p. of plates : ill. (some col.), maps (some col.).

Pande, S. (2000). GIS application in cropping system analysis : case studies in Asia : proceedings of the International Workshop on Harmonization of Databases for GIS Analysis of Cropping Systems in the Asia Region : 18-29 August 1997, ICRISAT, Patancheru, India. Patancheru, Andhra Pradesh, India, ICRISAT, 2000. 91 p. : ill. (some col.), col. maps.

Pierce, F. J. and D. D. Warncke (2000). "Soil and crop response to variable-rate liming for two Michigan fields." Soil Sci Soc Am j 64(2): 774-780.
Soil pH is known to vary spatially, making variable-rate lime application attractive where soil acidity occurs. This study examined the efficacy of variable-rate lime applications based on grid sampling at various scales on soil pH and the yield of corn (Zea mays L.) and soybean [Glycine max L.(Merr.)] during 3 yr. Lime was applied in two fields according to five lime management strategies: lime requirement (LR) estimated from maps interpolated from soil samples obtained from 30.5-, 61-, and 91.5-m grids; LR determined for the plot; and no lime. The LR interpolations consistently underestimating and were even not correlated with LR measured on each plot. Granulated lime, used to insure uniform lime application, was slow to react in the field and a lab incubation verified that it reached much slower than agricultural lime. Changes in pH occurred in the surface 10 cm, reflecting the depth of lime incorporation by chisel plowing. Corn yield did not respond to liming in 1995 and 1996. Soybean yield in 1997 increased due to liming at the Durand field, which had a lower range of soil pH values. Normalized soybean yields at both fields followed the same linear-plateau response to pH, with soybean yields declining below a threshold pH of about 5.9. While there is need for improvements in grid sampling design, variable lime applications under all of the grid sampling scales increased soil pH above the threshold pH for soybean in these fields, resulting in an improvement compared with whole field management.

Plant, R. E., D. S. Munk, et al. (2000). "Relationships between remotely sensed reflectance data and cotton growth and yield." Trans ASAE 43(3): 535-546.
Remotely sensed electromagnetic reflectance data can provide at relatively low cost a set of detailed, spatially distributed data on plant growth and development. Vegetation indices based on algebraic combinations of different wavelength bands are especially useful in summarizing reflectance data. One of the most commonly used vegetation indices is the normalized difference vegetation index, or NDVI. The objective of this study was to determine whether measurements based on the NDVI could provide information useful for site-specific management of cotton. Aerial photographs were taken of replicated Acala cotton field experiments in California in which the treatment was water or nitrogen stress level. NDVI integrated over time showed a significant correlation with lint yield in those experiments in which there was a significant stress effect on yield. The spatiotemporal pattern of NDVI reflected stress factors and was approximately coincident with the onset of measurable water stress. NDVI tended to indicate the presence of nitrogen stress even in those cases where the stress did not result in a significant yield reduction. In a study of the correlation of NDVI with late season plant mapping indices NDVI was correlated with nodes above white flower and strongly correlated with nodes above cracked boll. An alternative vegetation index, the relative nitrogen vegetation index, was not better than NDVI as an indicator of nitrogen stress.

Reyns, P., P. Spaepen, et al. (2000). "Site-specific relationship between grain quality and yield." Precis agric 2(3): 231-246.

Righetti, T. L. and M. D. Halbleib (2000). "Pursuing precision horticulture with the internet and a spreadsheet." HortTechnology 10(3): 458-467.
Agriculture is changing. State-of-the-art computer systems that use GPS (global positioning systems) data, GIS (geographic information systems) software, remotely sensed images, automated sampling, and information analysis systems are transforming growers' ability to produce their crops. Currently, the farm service and agricultural sales industry, rather than the grower direct most information technology applications. Precision agriculture must become an information-driven and grower-driven process. Data evaluation has to be made simpler, less time consuming, and inexpensive. The purpose of this paper is to outline potential strategies and demonstrate how information can be processed and evaluated with readily available and inexpensive analytical tools.

Roberson, G. T. (2000). "Precision agriculture technology for horticultural crop production." HortTechnology 10(3): 448-451.
Precision agriculture is a comprehensive system that relies on information, technology and management to optimize agricultural production. While used since the mid-1980s in agronomic crops, it is attracting increasing interest in horticultural crops. Relatively high per acre crop values for some horticultural crops and crop response to variability in soil and nutrients makes precision agriculture an attractive production system. Precision agriculture efforts in the Department of Biological and Agricultural Engineering at North Carolina State University are currently focused in two functional areas: site-specific management and postharvest process management. Much of the information base, technology, and management practices developed in agronomic crops have practical and potentially profitable applications in fruit and vegetable production. Mechanized soil sampling, pest scouting and variable rate control systems are readily adapted to horticultural crops. Yield monitors are under development for many crops that can be mechanically harvested. Investigations have begun to develop yield monitoring capability for hand harvested crops. Postharvest controls are widely used in horticultural crops to enhance or protect product quality.

Robert, P. C. (2000). "Site-specific management for the twenty-first century." HortTechnology 10(3): 444-447.
A better awareness of soil and crop condition variability within fields brought the notion, in the early 1980s that variable management within fields by zones rather than whole fields would increase profitability by doing the right thing at the right place in the right way. At the same time, the microcomputer became available and made possible the acquisition, processing, and use of spatial field data as well as the development of a new kind of farm machinery with computerized controllers and sensors. Precision agriculture (PA) has been considered for most common cropping systems and some specialty crops, worldwide. It is particularly well adapted to high value crops such as many horticultural crops. PA is still in infancy and its adoption varies greatly but precision agriculture is the agricultural system of the future. It offers a variety of potential benefits in profitability, productivity, sustainability, crop quality, food safety, environmental protection, on-farm quality of life, and rural economic development.

Rooney, D. J. and B. Lowery (2000). "A profile cone penetrometer for mapping soil horizons." Soil Sci Soc Am j 64(6): 2136-2139.
Accurate soil mapping at a fine scale is needed for site-specific farming, research on solute transport, and many other applications requiring detailed analysis of both the depth and thickness of soil horizons. Soil mapping techniques currently used are too costly to address the spatial variability of soil mapping units. We propose the use of a profile cone penetrometer (PCP) to assist in mapping soil properties at a landscape scale. Data collected with the PCP show clear changes in soil properties with depth, and were confirmed using profile descriptions from soil pits as well as 4.3-cm-diam soil cores. Combining three-dimensional PCP data with soil attribute information will provide a rapid and effective means to digitally update soil surveys and improve the efficiency and cost effectiveness of sampling techniques.

Sadler, E. J., P. J. Bauer, et al. (2000). "Site-specific analysis of a droughted corn crop. II. Water use and stress." Agron j 92(3): 403-410.

Sadler, E. J., P. J. Bauer, et al. (2000). "Site-specific analysis of a droughted corn crop. I. Growth and grain yield." Agron j 92(3): 395-402.

Sadler, E. J., B. K. Gerwig, et al. (2000). "Site-specific modeling of corn yield in the SE coastal plain." Agric syst 64(3): 189-207.

Saraiva, A. M., A. R. Hirakawa, et al. (2000). "A weighing system for grab loaders for sugar cane yield mapping." Precis agric 2(3): 293-309.

Schneider, A. D. and T. A. Howell (2000). "Surface runoff due to LEPA and spray irrigation of a slowly permeable soil." Trans ASAE 43(5): 1089-1095.

Schroder, J. J., J. J. Neeteson, et al. (2000). "Does the crop or the soil indicate how to save nitrogen in maize production? Reviewing the state of the art. [Erratum: Sept 29, 2000, v. 68 (1), p. 85.]." Field crops res 66(2): 151-164.

Sembiring, H., H. L. Lees, et al. (2000). "Effect of growth stage and variety on spectral radiance in winter wheat." J plant nutr 23(1): 141-149.
Before sensor-based variable rate technology (VRT) can be used to reduce nitrogen (N) fertilizer rates in winter wheat (Triticum aestivum L.) spectral radiance readings must be understood. One prominent issue is the impact of crop growth stage on spectral radiance readings, and the ensuing problem of relating databases gathered at different locations and different stages of growth. In order to evaluate the impact of growth stage on spectral radiance, sensor readings were taken from a winter wheat variety trial and two long-term N and phosphorus (P) fertility trials. The normalized difference vegetative index was computed using red and near infrared (NIR) spectral radiance measurements [NDVI=(NIR-red)/(NIR+red)]. Total N uptake in winter wheat at Feekes growth stages 4, 5, 7, and 8 was highly correlated with NDVI. In the variety trial, non-significant differences in NDVI readings were noticed between the five common genotypes (by growth stage) grown in this region. However, slopes from linear regression of total N uptake on NDVI were different at different stages of growth, which suggests the need for growth stage specific calibration. Freeze injury (altered tissue color) affected the relationship between total N uptake and NDVI, however, NDVI continued to be a good predictor of in-season total N uptake in wheat even though cell blasting altered tissue color. This work showed that NDVI is a good predictor of biomass, but not necessarily total N concentration in plant tissue. The amount of variability in total N uptake as explained by NDVI increased with advancing growth stage (Feekes 4 to 7), largely due to an increased percentage of soil covered by vegetation.

Senay, G. B. and R. L. Elliott (2000). "Combining AVHRR-NDVI and landuse data to describe temporal and spatial dynamics of vegetation." For ecol manage 128(1/2): 83-91.

Solie, J. B. (2000). "The impact of precision farming strategies on profitability."

Spaner, D., D. B. McKenzie, et al. (2000). "Six years of adaptive and on-farm spring cereal research in Newfoundland." Can j plant sci 80(1): 205-216.

Stafford, J. V. (2000). "Implementing precision agriculture in the 21st century." J agric eng res 76(3): 267-275.

Stelljes, K. B. (2000). "New systems research targets precision agriculture's effectiveness." Agric res 48(10): 16-18.

Stoll, A. and H. D. Kutzbach (2000). "Guidance of a forage harvester with GPS." Precis agric 2(3): 281-291.

Stombaugh, T. S. and S. Shearer (2000). "Equipment technologies for precision agriculture." J soil water conserv 55(1): 6-11.

Thompson, W. (2000). "Farming in the zone." Calif grow 24(6): 6-7.

Verhagen, A., A. Stein, et al. (2000). "Use of wavelets to compare simulated yield patterns for precision agriculture at the field scale." Precis agric 2(4): 333-346.

Viscarra Rossel, R. A. and A. B. McBratney (2000). "A two-factor empirical deterministic response surface calibration model for site-specific predictions of lime requirement." Precis agric 2(2): 163-178.

Walters, A. (2000). "Using visual information for precision farming." Calif grow 24(5): 18-20.

Weise, G., Y. Nagasaka, et al. (2000). "An investigation of the turning behavior of an autonomous rice transplanter." J agric eng res 77(2): 233-237.
A relationship was established between the steering angle and the turning radius of an autonomous four-wheeled, rice transplanter travelling in a paddy field. The transplanter was operated at three different forward speeds in circular paths in a flooded paddy field. The vehicle position was measured using real-time kinematic global positioning system. Measured values were compared with theoretical values of turning radii obtained by a geometrical vehicle model. The predicted turning radius, however, was much smaller than the measured turning radius, the difference being attributed to poor lateral support of the tyres when operating on the soft top soil of a flooded paddy field.

Westervelt, J. D. and H. F. Reetz (2000). GIS in site-specific agriculture. Danville, Ill., Interstate Publishers, c2000. v, 58 p. : ill. (some col.).

Whelan, B. M. and A. B. McBratney (2000). "The "null hypothesis" of precision agriculture management." Precis agric 2(3): 265-279.

White, J. W. and P. R. Grace (2000). Modeling extremes of wheat and maize : crop performance in the tropics : proceedings of a workshop, CIMMYT, El Batan, Mexico, 19-22 April 1999. Mexico, International Maize and Wheat Improvement Center, Natural Resources Group, c2000. iv, 70 p. : ill.

Williams, M. M., II, R. Gerhards, et al. (2000). "Two-year weed seedling population responses to a post-emergent method of site-specific weed management." Precis agric 2(3): 247-263.

Wilson, J. N. (2000). "Guidance of agricultural vehicles--a historical perspective." Comput electron agric 25(1/2): 3-9.
This article provides a brief overview of research efforts over the past 50 years directed toward the development of guidance systems for agricultural vehicles. The motivations for and potential advantages of autonomous or semi-autonomous systems are discussed. Examples are presented of the two general approaches taken; namely, guidance with respect to a directrix generated by the previous pass, or guidance with respect to a directrix generated by fixed points in the field. From this review, it is concluded that two recent technologies, specifically computer vision and the global positioning system, possess the technological features and characteristics most closely resembling those possessed by the human operator for implementation of a vehicle guidance system.

Yang, C., J. H. Everitt, et al. (2000). "Mapping grain sorghum growth and yield variations using airborne multispectral digital imagery." Trans ASAE 43(6): 1927-1938.
Airborne digital imagery is becoming an increasingly important data source for precision agriculture. In this study, airborne digital imagery and yield monitor data were used to map plant growth and yield variability. Color-infrared (CIR) images were acquired from a grain sorghum field five times during the 1998 growing season, and yield monitor data were also collected from the field during harvest. The images were georeferenced and then classified into zones of homogeneous spectral response using unsupervised classification procedures. The images and unsupervised classification maps clearly revealed the consistency and change of plant growth patterns over the growing season. Correlation analyses showed grain yield was significantly related to the individual near-infrared (NIR), red, and green bands of the CIR images and the normalized difference vegetation index (NDVI) for the five dates. Stepwise linear regression was also used to relate yield to the three bands for each of the five dates, and the three images obtained at and after the peak growth produced higher R2-values (0.64, 0.66, and 0.61) than the other two early season images (0.39 and 0.37). Yield maps generated from the three best images agreed well with a yield map from the yield monitor data. These results demonstrated that airborne digital imagery can be a very useful data source for detecting plant growth and yield variability for precision agriculture.

Yang, C. and G. L. Anderson (2000). "Mapping grain sorghum yield variability using airborne digital videography." Precis agric 2(1): 7-23.
Mapping crop yield variability is one important aspect of precision agriculture. Combine mounted yield monitors are becoming widely available for measuring and mapping yields for different crops. This study was designed to assess airborne digital videography as a tool for mapping grain sorghum yields for precision farming. Color-infrared (CIR) imagery was acquired with a three-camera digital video imaging system from two grain sorghum fields in south Texas over the 1995 and 1996 growing seasons. The multispectral video data obtained during the bloom to soft dough stages of plant development were related to hand-harvested grain yields at sampling sites determined from unsupervised image classification maps of the two fields. Significant correlations were found between grain yields and the red band, the green band, and the normalized difference vegetation index (NDVI). Regression equations were developed to describe the relations between grain yields and each of the three significant spectral variables using an exponential model and two segmented models. Multiple linear regression equations were also determined to relate grain yields to the three bands and NDVI. These equations were then used to estimate grain yields at each video image pixel within each field and to generate grain yield maps. Comparisons of the estimated average yields from the regression equations with the actual yields indicated that yield estimation errors from the equations ranged from 0.0 to 10.0% in 1995 and from 0.2 to 7.3% in 1996 for field 1, and from 4.0 to 11.2% in 1995 and 6.3 to 12.5% in 1996 for field 2. Although the equations developed for one field in a given year may not apply.

Yao, H. and R. L. Clark (2000). "Development of topographic maps for precision farming with medium accuracy GPS receivers." Appl eng agric 16(6): 629-636.

Yao, H. and R. L. Clark (2000). "Evaluation of sub-meter and 2 to 5 meter accuracy GPS receivers to develop digital elevation models." Precis agric 2(2): 189-200.

(2001). Issues in the management of agricultural resources : proceedings of a seminar in commemoration of FFTC's 30th anniversary, National Taiwan University, Taipei, Taiwan, ROC, September 6-8, 2000. Taipei, Taiwan, Food & Fertilizer Technology Center, 2001. xvi, 259 p. : ill., col. maps.

(2001). Cropping Systems and Water Quality Research Unit. Columbia, Mo., USDA, ARS, The Unit, [2001]-.
The mission of Cropping Systems and Water Quality Research Unit is to develop knowledge and technology to optimize yields from crop production systems while minimizing erosion and enhancing water and soil quality.

(2001). Proceedings, third International Conference on Geospatial Information in Agriculture and Forestry : 5-7 November 2001, Denver, Colorado, USA. Ann Arbor, MI, Veridian, c2001. 1 CD-ROM : col.

Auernhammer, H. (2001). "Precision farming--the environmental challenge." Comput electron agric 30(1/3): 31-43.
Precision farming makes use of information technologies in agriculture. With the satellite positioning system and electronic communication standards, position and time may be integrated into all procedures connected to farming. Today, precision farming is primarily geared towards site-specific application of fertilisers with the resulting cost advantages being quite small. Thus, precision farming will likely gain in importance only when viable additional benefits, such as reduced environmental burdens and increased flow of information, are recognised and evaluated and become part of the reward itself.

Bailey, J. S., K. Wang, et al. (2001). "Use of precision agriculture technology to investigate spatial variability in nitrogen yields in cut grassland." Chemosphere 42(2): 131-140.

Basso, B., J. T. Ritchie, et al. (2001). "Spatial validation of crop models for precision agriculture." Agric syst 68(2): 97-112.

Bergeijk, J. v., D. Goense, et al. (2001). "Soil tillage resistance as a tool to map soil type differences." J agric eng res 79(4): 371-387.
Precision agriculture is based on spatial knowledge of soil and crop conditions in the management decisions. In this paper, a method to improve determination of soil physical properties is proposed. Current practice is to analyse soil samples, taken at several locations in a field, for physical properties. To obtain a sound coverage, many soil samples have to be analysed. When soil properties are correlated, it is possible to reduce the number of soil samples of one property and enhance its spatial resolution with the information of another, more densely sampled, property. In this study, information gathered automatically during the major soil tillage operation, ploughing, is used to improve the spatial resolution of sampled topsoil clay content. Plough draught was measured during two seasons on a 6 ha field. The specific plough draught varied between 30 and 50 kN m(-2). Clay content varied between 6 and 22% and topsoil moisture content range was 120-240 g kg(-1) during the first year and 180-300 g kg(-1) in the second year. The specific plough draught maps of both years showed a similar spatial pattern with a cross correlation coefficient at zero distance of 0.6. The use of specific plough draught as co-variable in the co-kriging technique made it possible to decrease the number of topsoil clay content samples from 60 to 18 ha(-1) with only 20% increase in prediction error. On this field, the spatial variation in top soil clay content was correlated with the spatial variation of the crop yield.

Bergeijk, J. v., D. Goense, et al. (2001). "Dynamic weighing for accurate fertilizer application and monitoring." J agric eng res 80(1): 25-35.
The mass flow of fertilizer spreaders must be calibrated for the different types of fertilizers used. To obtain accurate fertilizer application manual calibration of actual mass flow must be repeated frequently. Automatic calibration is possible by measurement of the actual mass flow, based on dynamic weighing of the spreader. This paper describes the design and test of a dynamic weighing system. Under field conditions, this system was able to provide force due to spreader weight readings that have a standard deviation of 20 N, over a measurement range of 6-20 kN, at a maximum time delay of 1 s. Time-stamped data logging of the spreader weight and the theoretical application rate combined with position information allows determination of the realized spatial application of fertilizer. A comparison can be made between realized and prescribed application rates. This information is necessary for evaluation of fertilizer management in a precision agriculture farming system and to accurately target fertilizer application to crop and soil status.

Bongiovanni, R. and J. Lowenberg DeBoer (2001). Precision agriculture : economics of nitrogen management in corn using site-specific crop response estimates from a spatial regression model. [Ames, Iowa?], American Agricultural Economics Association, 2001.

Bouma, J. (2001). "The role of soil science in the land use negotiation process." Soil use manage 17(1): 1-6.
The hierarchial concept of land use planning becomes less relevant in a society with continuous interactions between stakeholders, researchers, planners and politicians. In this context, land use negotiation rather than land use planning appears to be the most appropriate concept. In the negotiation process, good quality data about the land is important as land properties are, obviously, key elements to be considered. Case studies at farm and regional level have been analysed to explore answers to a number of questions. How can soil data be presented most effectively? What are the research needs? How can the large existing body of data be mobilized most effectively? Studies on regional land use in Costa Rica used methods in a logical sequence including projections, explorations and predictions of land use patterns. The work involved upscaling of data, obtained at farm level, to the regional level. Work at farm level focussed on prototyping procedures in which farming systems were 'designed' by close interaction between farmers and scientists, including applications of precision agriculture. Soil data demands were analysed, emphasizing the effects of using data with different degrees of detail together with the application of pedotransfer functions which effectively transform existing data into parameters that are difficult or expensive to measure directly. This not only facilitated interactions with stakeholders but also with colleague scientists in interdisciplinary teams. In addition, use of Geographical Information Systems allowed visual presentations of alternative geographical land use patterns that were associated with various scenarios, thereby facilitating the.

Chen, X., C. Xu, et al. (2001). "An analysis of relationships among plant community phenology and seasonal metrics of Normalized Difference Vegetation Index in the northern part of the monsoon region of China." Int j biometeorol 45(4): 170-177.
This study focuses on relationships between the phenological growing season of plant communities and the seasonal metrics of Normalized Difference Vegetation Index (NDVI) at sample stations and pixels overlying them, and explores the procedure for determining the growing season of terrestrial vegetation at the regional scale, using threshold NDVI values obtained by surface-satellite analysis at individual stations/pixels. The cumulative frequency of phenophases has been calculated for each plant community and each year in order to determine the growing season at the three sample stations from 1982 to 1993. The precise thresholds were arbitrarily set as the dates on which the phenological cumulative frequency reached 5% and 10% (for the beginning) and 90% and 95% (for the end). The beginning and end dates of the growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from NDVI curves for 8-km2 pixels overlying the phenological stations. According to a trend analysis, a lengthening of the growing seasons and an increase of the integrated growing season NDVI have been detected in the central part of the research region. The correlation between the beginning dates of the growing season and the corresponding threshold NDVI values is very low, which indicates that the satellite-sensor-derived greenness is independent of the beginning time of the growing season of local plant communities. Other than in spring, the correlation between the end dates of the growing season and the corresponding threshold NDVI values is highly significant. The negative correlation shows that the earlier the growing season terminates, the larger the.

Elms, M. K., C. J. Green, et al. (2001). "Variability of cotton yield and quality." Commun soil sci plant anal 32(3/4): 351-368.
Precision agriculture technologies offer an opportunity to vary production inputs within a field. Variable rate application offers the potential to increase production efficiency and minimize potential adverse environmental effects of agricultural chemicals. As an initial step in the development of precision agriculture technologies for cotton, studies are needed to document variability of cotton. The primary objective of this study was to document variability of yield and quality of irrigated cotton within and across three growing seasons. This study was conducted on a 5.3 ha irrigated field located at the Erskine Research Farm at Texas Tech University, Lubbock, TX. The crop was grown under a conventional tillage system with a 1.0 m row spacing. With the exception of sample collection, the field was managed traditionally with respect to production inputs. A grid system (57 points) was established on 30.5 m (approximately 0.1 ha) intervals. Production of fruiting sites, fruit retention, lint yield, fiber length, strength, micronaire, and gross revenue were estimated for each grid point. Soil chemical and physical properties were also determined for each grid point. Highest variability was observed for lint yield and production of fruiting sites, and lowest variability was observed for lint quality parameters. Yield was correlated to production of fruiting sites each season. Nitrate concentrations were highly variable, and yield was negatively correlated to nitrogen (N) in 1997. This suggests that variable application of N may be a viable management option in the future. Yield was positively correlated to calcium (Ca), pH, and CEC in 1997. Yield variability was.

Fraisse, C. W., K. A. Sudduth, et al. (2001). "Delineation of site-specific management zones by unsupervised classification of topographic attributes and soil electrical conductivity." Trans ASAE 44(1): 155-166.
The objective of this research was to determine if unsupervised classification of topographic attributes and soil electrical conductivity could identify management zones for use in precision agriculture. Data collected in two fields located in central Missouri were used to test the proposed methodology. Principal component analysis was used to determine which layers of data were most important for representing within-field variability. Unsupervised clustering algorithms implemented in geographic information system (GIS) software were then used to divide the fields into potential management zones. Grain yield data obtained using a full-size combine equipped with a commercial yield sensing system and global positioning system (GPS) receiver were used to analyze the "goodness" of the potential management zones defined for each field. Principal component analysis of input variables for Field 1 indicated that elevation and bulk soil electrical conductivity (EC) were more important attributes than slope and Compound Topographic Index (CTI) for defining claypan soil management zones. The optimum number of zones to use when dividing a field may vary from year to year and was mainly a function of weather and the crop planted. The number of zones decreased if adequate moisture conditions were present throughout the cropping season (unpredictable) or if crops tolerant to water stress were planted (predictable). This classification procedure is fast, can be easily automated in commercially available GIS software, and has considerable advantages when compared to other methods for delineating within-field management zones.

Gaston, L. A., M. A. Locke, et al. (2001). "Spatial variability of soil properties and weed populations in the Mississippi Delta." Soil Sci Soc Am j 65(2): 449-459.
Simulation models and precision agriculture practices may require more detail and certainty about soil spatial variability than provided by soil surveys. This study described soil and weed spatial variability in 50-ha subareas of two sites included in the Mississippi Delta Management Systems Evaluation Areas project. Objectives were (i) to describe the spatial variability of soil properties and (ii) to determine relationships between spatially variable weed populations and soil properties. Surface soil samples were collected at nodes of 60-m square grids prior to planting cotton (Gossypium hirsutum L.) in 1996. Field-moist soil was analyzed for microbial activity. Air-dried soil was used to determine soil organic C, pH, and texture. Fluometuron and either clomazone, metolachlor, or norflurazon were banded over the crop row at planting. Weed counts were taken 6 wk after herbicide application. The spatial variability of soil properties and weed populations was described using geostatistics. Soil microbiological activity exhibited limited spatial dependence, but pH, organic C, and texture semi-variograms were well-described with spherical models. Although short-range (<60 m) variability was often high, the range of spatial dependence typically exceeded 120 m. Total weeds were spatially dependent both years; however, weeds susceptible to control by herbicide were not. Weed densities were significantly greater (P < 0.05) in areas that had higher organic C and finer texture. Areas of low organic C and coarse soil often had no weeds. Thus, more uniform weed control might be achieved by varying preemergence herbicide application rate. Acceptable weed control might be achieved with lower herbicide application.

Gerard, B. and A. Buerkert (2001). "Estimation of spatial variability in pearl millet growth with non-destructive methods." Exp agric 37(3): 373-389.
Growth variability in pearl millet (Pennisetum glaucum) over short distances is a severe constraint on the interpretation of agricultural experiments in the West African Sahel. The purpose of this study, therefore, was to compare different non-destructive methods to estimate, spatially, millet growth and final yields. Aerial photography, georeferenced radiometric measurements and a chlorophyll meter were tested during three rainy seasons in a nitrogen rate x density x genotype experiment in western Niger. For the radiometric measurements, normalized difference vegetation indices (NDVI) obtained and calibrated for individual millet hills spaced 1.5 m apart were aggregated for the entire experiment with 6000 samples per hectare. A simple calibration procedure was used to correct for variation in soil background reflectance and incident light. For NDVI measurements of individual planting hills, the correlation between plant total dry matter (TDM), leaf weight, leaf area and NDVI was high (r2 = 0.89-0.91) and regression parameters were genotype-specific. Aggregated georeferenced NDVI measurements at the plot level correlated with grain and TDM at harvest (r2 = 0.40-0.87). The analysis of true-colour and infrared aerial photographs permitted the monitoring of millet growth and the quantitative evaluation of treatment responses throughout the growing season. The infrared images were the most efficient in the detection of vegetation followed by the normalized green band of true-colour images. The red band was the least effective because of the influence of soil albedo and image vignetting. Although chlorophyll meter measurements reflected relative differences in plant nitrogen status between.

Grace, P. R. and J. W. White (2001). Directions in modeling wheat and maize for developing countries : proceedings of a workshop, CIMMYT, El Batan, Mexico, 4-6 May 1998. Mexico, CIMMYT, c2001. vi, 42 p. : ill. (some col.), maps.

Halls, P. J. (2001). Spatial information and the environment. London ; New York, Taylor & Francis, 2001. xiv, 284 p. : ill., maps.

Hartkamp, A. D. (2001). Maize production environments revisited : a GIS-based approach. Mexico, D.F., Natural Resources Group, CIMMYT, 2001. 33 p. : col. maps.

Holmstrom, K. E., M. G. Hughes, et al. (2001). "Spatial mapping of adult corn earworm and European corn borer populations in New Jersey." HortTechnology 11(1): 103-109.
In 1998, Rutgers Cooperative Extension (RCE) and the Grant F. Walton Center for Remote Sensing and Spatial Analysis (CRSSA) at Rutgers University began a joint program to use global positioning system (GPS) and geographic information systems (GIS) technologies to map the spatial distribution of corn earworm (Helicoverpa zea Boddie (Lepidoptera:Noctuidae)) and European corn borer (Ostrinia nubilalis Hubner (Lepidoptera:Pyralidae)). In 1999 the Rutgers Cooperative Extension Vegetable Integrated Pest Management (IPM) Program operated a network of 81 blacklight insect survey traps in New Jersey. These 15 W blacklight traps were used to monitor adult populations of vegetable crop pests including corn earworm and European corn borer. All blacklight trap sites were mapped using a hand held GPS unit. Average daily corn earworm and European corn borer population data were imported into a GIS software package, and then linked to corresponding mapped locations throughout New Jersey. State wide spatial distributions of adult corn earworm and European corn borer populations were produced weekly, and distributed via extension newsletters and web sites to augment the current RCE IPM outreach program.

Johnson, C. K., J. W. Doran, et al. (2001). "Field-scale electrical conductivity mapping for delineating soil condition." Soil Sci Soc Am j 65(6): 1829-1837.
Traditional sampling methods are inadequate for assessing the interrelated physical, chemical, and biological soil properties responsible for variations in agronomic yield and ecological potentials across a landscape. Recent advances in computers, global positioning systems, and large-scale sensors offer new opportunities for mapping heterogeneous patterns in soil condition. We evaluated field-scale apparent electrical conductivity (EC(a)) mapping for delineating soil properties correlated with productivity and ecological properties. A contiguous section of farmland (250 ha), managed as eight fields in a no-till winter wheat (Triticum aestivum L.)-corn (Zea mays L.)-millet (Panicum miliaceum L.)-fallow rotation, was EC(a) mapped (approximately equal to 0- to 30-cm depth). A geo-referenced soil-sampling scheme separated each field into four EC(a) classes that were sampled (0- to 7.5- and 7.5- to 30-cm depths) in triplicate. Soil physical parameters (bulk density, moisture content, and percentage clay), chemical parameters (total and particulate organic matter [POM], total C and N, extractable P, laboratory-measured electrical conductivity [EC(1:1)], and pH), biological parameters (microbial biomass C [MBC] and N [MBN], and potentially mineralizable N), and surface residue mass were significantly different among EC(a) classes (P less than or equal to 0.06) at one or both depths (0-7.5 and 0-30 cm). Bulk density, percentage clay, EC(1:1), and pH were positively correlated with EC(a); all other soil parameters and surface residue mass were negatively correlated. Field-scale EC(a) classification delimits distinct zones of soil condition, providing an effective basis for soil sampling. Potential uses.

Khanna, M. (2001). "Sequential adoption of site-specific technologies and its implications for nitrogen productivity: a double selectivity model." Am j agric econ 83(1): 35-51.

Kuhlmann, F. and C. Brodersen (2001). "Information technology and farm management: developments and perspectives." Comput electron agric 30(1/3): 71-83.
Our aspirations are pessimistic for the fast diffusion of complex and demanding information technology (IT) aids and decision support systems (DSSs) among farmers. This view arises from some results of the new institutional economics, recent results of empirical decision research, data from farmers applications of decision models, as well as experiences introducing farm-level DSSs by our own working group at Giessen. For some areas of decision making, one can only hope that the use of models heightens problem awareness by the user, thus providing additional insights into the usually complex decision space. If, however, farmers want to increase the economic efficiency of their production and marketing processes by decreasing waste and friction, then we must continue to develop and refine knowledge-based DSSs. Problem selection, however, should be driven by new results of empirical decision research. Because imperfect knowledge exists regarding the input-output relations of agricultural production systems, as well as about the time- and space-variant uncontrollable input variables, close co-operation with the biological disciplines of agricultural science is needed. Multi-disciplinary research and end user orientation seem to be the key factors for further progress.

Lamb, D. W. and R. B. Brown (2001). "Remote-sensing and mapping of weeds in crops." J agric eng res 78(2): 117-125.

Landres, P. B., D. R. Spildie, et al. (2001). GIS applications to wilderness management : potential uses and limitations. Fort Collins, CO, U.S. Dept. of Agriculture, Forest Service, Rocky Mountain Research Station, [2001] ii, 9 p. : ill., map.

Lark, R. M. (2001). "Some tools for parsimonious modelling and interpretation of within-field variation of soil and crop systems." Soil tillage res 58(3/4): 99-111.

LaRuffa, J. M., W. R. Raun, et al. (2001). "Optimum field element size for maximum yields in winter wheat, using variable nitrogen rates." J plant nutr 24(2): 313-325.
The resolution at which variability in soil test and yield parameters exist is fundamental to the efficient use of real-time sensor-based variable rate technology. This study was conducted to determine the optimum field element size for maximum yields in winter wheat (Triticum aestivm L.), using variable nitrogen (N) rates based on sensor readings. The effect of applying N at four different resolutions (0.84, 3.34,13.38, and 53.51 m(2)) on grain yield, N uptake and efficiency of use was investigated at Haskell, Hennessey, Perkins, and Tipton, Oklahoma. At Feekes growth stage 5 an optical sensor developed at Oklahoma State University measured red (670 +/- 6 nm) and near-infrared (NIR, 780 +/- 6 nm) reflectance in each subplot. A normalized-difference-vegetative-index (NDVI) was calculated from the sensor measurements. Nitrogen was applied based on a NDVI-N rate calibration. Nitrogen rate, yield, N uptake, and efficiency of use responses to treatment resolution and applied N fertilizer differed in the 3 years of this experiment. In the first year, no significant influence of resolution on N rate, yield, N uptake, or efficiency of use was observed, likely a result of a late freeze that drastically reduced yields. In the second year of the experiment, there was a trend for a lower N rate and a higher efficiency of use for the 0.84 m(2) resolution. In the third year of this study, there was a trend for a higher yield and a higher efficiency of use for the 53.51 m(2) resolution at both sites. In general, the finer resolutions tended to have increased efficiency of use in high yielding environments (> 2300 kg ha-1), and decreased yields in low yielding environments. This.

Lukina, E. V., K. W. Freeman, et al. (2001). "Nitrogen fertilization optimization algorithm based on in-season estimates of yield and plant nitrogen uptake." J plant nutr 24(6): 885-898.
Current methods of determining nitrogen (N) fertilization rates in winter wheat (Triticum aestivum L.) are based on farmer projected yield goals and fixed N removal rates per unit of grain produced. This work reports on an alternative method of determining fertilizer N rates using estimates of early-season plant N uptake and potential yield determined from in-season spectral measurements collected between January and April. Reflectance measurements under daytime lighting in the red and near infrared regions of the spectra were used to compute the normalized difference vegetation index (NDVI). Using a modified daytime lighting reflectance sensor, early-season plant N uptake between Feekes physiological growth stages 4 (leaf sheaths lengthen) through 6 (first node of stem visible) was found to be highly correlated with NDVI. Further analyses showed that dividing the NDVI sensor measurements between Feekes growth stages 4 and 6, by the days from planting to sensing date was highly correlated with final grain yield. This in-season estimate of yield (INSEY) was subsequently used to compute the potential N that could be removed in the grain. In-season N fertilization needs were then considered to be equal to the amount of predicted grain N uptake (potential yield times grain N) minus predicted early-season plant N uptake (at the time of sensing), divided by an efficiency factor of 0.70. This method of determining in-season fertilizer need has been shown to decrease large area N rates while also increasing wheat grain yields when each 1 m2 area was sensed and treated independently.

McKinion, J. M., J. N. Jenkins, et al. (2001). "Analysis of a precision agriculture approach to cotton production." Comput electron agric 32(3): 213-228.
The hope of precision agriculture is that through more precise timing and usage of seed, agricultural chemicals and irrigation water that higher economic yields can occur while enhancing the economic production of field crops and protecting the environment. The analyses performed in this manuscript demonstrate proof of concept of how precision agriculture coupled with crop simulation models and geographic information systems technology can be used in the cotton production system in the Mid South to optimize yields while minimizing water and nitrogen inputs. The Hood Farm Levingston Field, located in Bolivar County, Mississippi, next to the Mississippi River, was chosen as the test sight to obtain a one hectare soil physical property grid over the entire 201 ha field. The 1997 yield was used as a comparison for the analysis. Actual cultural practices for 1997 were used as input to the model. After the 201 simulations were made using the expert system to optimize for water and nitrogen on a one hectare basis, the model predicted that an increase of 322 kg/ha could be obtained by using only an average increase of 2.6 cm of water/ha and an average decrease of 35 kg N/ha.

Millington, A. C., S. J. Walsh, et al. (2001). GIS and remote sensing applications in biogeography and ecology. Boston, Kluwer Academic Publishers, c2001. vii, 333 p. : ill., maps 1 computer optical disc (4 3/4 in.).

Montello, D. R. (2001). Spatial information theory : foundations of geographic information science : international conference, COSIT 2001, Morro Bay, CA, USA, September 19-23, 2001 : proceedings. Berlin ; New York, Springer, 2001. xiv, 502 p. : ill., map.

Pachepsky, Y. A., D. J. Timlin, et al. (2001). "Soil water retention as related to topographic variables." Soil Sci Soc Am j 65(6): 1787-1795.
Digital elevation models were proposed and used as a data source to estimate soil properties. This study evaluated variability of texture and water retention of soils for a gently sloping 3.7-ha field located in the long-term precision farming research site at the Beltsville Agricultural Research Center, MD. The specific objectives of this research were (i) to characterize variability of water retention across the hillslope, and (ii) determine and describe any correlations of soil water retention with soil texture and surface topography. Soil was sampled along four 30-m transects and in 39 points within the study area. Textural fraction contents, bulk density, and water retention at 0, 2.5, 5.0, 10, 33, 100, 500, and 1500 kPa were measured in samples taken from 4- to 10-cm depth. A 30-m digital elevation model (DEM) was constructed from aerial photography data. Slopes, profile curvatures, and tangential curvatures were computed in grid nodes and interpolated to the sampling locations. Regressions with spatially correlated errors were used to relate water retention and texture to computed topographic variables. Sand, silt, and clay contents depended on slope and curvatures. Soil water retention at 10 and 33 kPa correlated with sand and silt contents. The regression model relating water retention to the topographic variables explained more than 60% of variation in soil water content at 10 and 33 kPa, and only 20% of variation at 100 kPa. Increases in slope values and decreases in tangential curvature values, i.e., less concavity or more convexity across the slope, led to the decreases in water retention at 10 and 33 kPa. Results of this work show a potential.

Padgitt, S., P. Petrzelka, et al. (2001). "Integrated crop management: the other precision agriculture." Am J altern agric 16(1): 16-22.
"Precision agriculture" was a favorite buzzword in agricultural discussions in the 1990s. Proponents of precision agriculture note its promises are twofold: economic benefits for the producer and environmental benefits for society. These benefits are to be achieved by improving the efficiency of input use, based on data obtained with global positioning systems (GPS) and geographic information systems (GIS) technologies. Although fulfillment of these promises has been mixed to date, it appears that "precision agriculture" will continue in the agriculture vernacular into the 21st century. In this article, we propose another sense of the term, and argue that precision agriculture, or at least long strides in that direction, is possible short of these highly complex methods and capital investments, through integrated crop management (ICM). As practiced by the producer and/or provided by independent crop consultants, ICM is one alternative to providing information-intensive management on the farm, and has proven efficiency of input use. That is, the promise of economic and environmental benefits holds true in a manner that makes it possible for any producer to implement "precision agriculture." Using data from users and nonusers of independent crop consultants implementing ICM, this study reveals that several economic and environmental benefits are gained from the information and management recommendations provided by consultants. Pest and nutrient management recommendations have led to decreases in pesticide and commercial fertilizer use. For the majority of users, these input reductions have resulted in an increase in profits since hiring a consultant. Users.

Pelletier, M. G. (2001). "Adaptive signal processing for removal of impulse noise from yield monitor signals." J cotton sci 5(4): 224-233.
The use of precision agriculture has driven the need for yield monitors. Yield monitors used for research require more rigorous standards of measurement in order to provide spatial data at a finer grid size than typically used in an on-farm application. The objective of this study was to develop a method for load-yield monitors to correct for impulse noise that occurs whenever a harvester drives over a hole, ditch, or large rocks. Removing such artifacts of the instrument will improve the quality of the data obtained over a shorter grid size, which is more appropriate for research requirements than are the typical large grid sizes of commercial yield monitors currently in use. The system developed demonstrated a reduction in impulse noise through the use of an accelerometer to obtain the impulse noise response, which was then used in an adaptive noise-cancellation signal processing technique to reduce impulse noise in the yield signal.

Plant, R. E. (2001). "Site-specific management: the application of information technology to crop production." Comput electron agric 30(1/3): 9-29.
Site-specific management (SSM; also called, precision agriculture) is the management of agricultural crops at a spatial scale smaller than that of the whole field. Widespread farmer adoption of SSM practices is contingent on its economic advantage. Three criteria that must be satisfied in order for SSM to be justified are, (1) that significant within-field spatial variability exists in factors that influence crop yield, (2) that, causes of this variability can be identified and measured, and (3) that, the information from these measurements can be used to modify crop management practices to increase profit or decrease environmental impact. The objective of this paper is to review the state of SSM at the turn of the millennium and to offer some speculation as to its future course. The review is organized around the essential components of SSM listed above, i.e. measuring spatial variability, analyzing the data obtained from these measurements, using information gained from this analysis to effect changes in management practices, and determining whether the resulting benefits are worth the costs. The discussion section considers some potential effects of large-scale adoption of SSM, should this adoption occur.

Raun, W. R., J. B. Solie, et al. (2001). "In-season prediction of potential grain yield in winter wheat using canopy reflectance." Agron j 93(1): 131-138.
Nitrogen fertilization rates in cereal production systems are generally determined by subtracting soil test N from a specified N requirement based on the grain yield goal, which represents the best achievable grain yield in the last 4 to 5 yr. If grain yield could be predicted in season, topdress N rates could be adjusted based on projected N removal. Our study was conducted to determine if the potential grain yield of winter wheat (Triticum aestivum L.) could be predicted using in-season spectral measurements collected between January and March. The normalized difference vegetation index (NDVI) was determined from reflectance measurements under daytime lighting in the red and near-infrared (NIR) regions of the spectra. In-season estimated yield (EY) was computed using the sum of two postdormancy NDVI measurements (Jan. and Mar.) divided by the cumulative growing degree days (GDD) from the first to second reading. A significant relationship between grain yield and EY was observed (R2 = 0.50, P > 0.0001) when combining all nine locations across a 2-yr period. Our estimates of potential grain yield (made in early Mar.) differed from measured grain yield (mid-July) at three sites where yield-altering factors (e.g., late summer rains delayed harvest and increased grain yield loss due to lodging and shattering) were encountered after the final sensing. Evaluating data from six of the nine locations across a 2-yr period, EY values explained 83% of the variability in measured grain yield. Use of EY may assist in refining in-season application of fertilizer N based on predicted potential grain yield.

Rew, L. J. and R. D. Cousens (2001). "Spatial distribution of weeds in arable crops: are current sampling and analytical methods appropriate." Weed res 41(1): 1-18.

Reynolds, K. M. (2001). Fuzzy logic knowledge bases in integrated landscape assessment : examples and possibilities. Portland, OR, U.S. Dept. of Agriculture, Forest Service, Pacific Northwest Research Station, [2001] 24 p. : ill., maps.

Runquist, S., N. Zhang, et al. (2001). "Development of a field-level geographic information system." Comput electron agric 31(2): 201-209.

Singh, R. B., J. Fox, et al. (2001). Land use and cover change. Enfield, NH, Science Publishers, c2001. xi, 299 p. : ill. (some col.), maps (some col.).

Sparovek, G. and E. Schnug (2001). "Soil tillage and precision agriculture a theoretical case study for soil erosion control in Brazilian sugar cane production." Soil tillage res 61(1/2): 47-54.

Sudduth, K. A., S. T. Drummond, et al. (2001). "Accuracy issues in electromagnetic induction sensing of soil electrical conductivity for precision agriculture." Comput electron agric 31(3): 239-264.
Soil apparent electrical conductivity (EC(a)) has been used as a surrogate measure for such soil properties as salinity, moisture content, topsoil depth (TD), and clay content. Measurements of EC(a) can be accomplished with commercially available sensors and can be used to efficiently and inexpensively develop the dense datasets desirable for describing within-field spatial variability in precision agriculture. The objective of this research was to investigate accuracy issues in the collection of soil EC(a) data. A mobile data acquisition system for EC(a) was developed using the Geonics EM38 sensor. The sensor was mounted on a wooden cart pulled behind an all-terrain vehicle, which also carried a GPS receiver and data collection computer. Tests showed that drift of the EM38 could be a significant fraction of within-field EC(a) variation. Use of a calibration transect to document and adjust for this drift was recommended. A procedure was described and tested to evaluate positional offset of the mobile EM38 data. Positional offset was due to both the distance from the sensor to the GPS antenna and the data acquisition system time lags. Sensitivity of EC(a) to variations in sensor operating speed and height was relatively minor. Procedures were developed to estimate TD on claypan soils from EC(a) measurements. Linear equations of an inverse or power function transformation of EC(a) provided the best estimates of TD. Collection of individual calibration datasets within each surveyed field was necessary for best results. Multiple measurements of EC(a) on a field were similar if they were obtained at the same time of the year. Whole-field maps of EC(a)-determined TD from.

Sullivan, M., T. VanToai, et al. (2001). "Evaluating on-farm flooding impacts on soybean." Crop sci 41(1): 93-100.
Flooding is a major problem that reduces soybean [Glycine max (L.) Merr.] growth and grain yield in many areas of the USA and the world. Our objective was to identify the plant and soil characteristics associated with different flooding durations in six fields in central Ohio. The soybean plants were at the V2 and V3 stages when rainfall-induced flooding occurred. The outer perimeters of the flooded areas were mapped, using GPS (global positioning system) technology, several times during the flooding event to delineate the change of the flooded area over time. Two 9-m wide transects across the flooded area within each field were divided into plots of 9 m by 9 m according to flooding duration: no flooding, 1 to 3 d, 4 to 6 d, and 6 to 8 d. Soil and plant nutrient levels, grain yield data and grain protein and oil content were determined for each plot. The soil cation-exchange capacity (CEC), pH, P, Ca, Mn, and Zn concentrations had significant positive correlation with flooding duration. There was a significant negative correlation of flooding duration with the population, height, number of pods, and yield of soybean. There was no significant correlation of flooding duration with seed weight, oil, or protein content of the seeds. Leaf tissue Ca, Mg, B, Fe, Cu, and Al concentrations had a significant positive correlation with flooding duration, whereas leaf tissue N concentration had a significant negative correlation with flooding duration.

Thomson, A. J. and D. L. Schmoldt (2001). "Ethics in computer software design and development." Comput electron agric 30(1/3): 85-102.
Over the past 20 years, computer software has become integral and commonplace for operational and management tasks throughout agricultural and natural resource disciplines. During this software infusion, however, little thought has been afforded human impacts, both good and bad. This paper examines current ethical issues of software system design and development in relation to privacy, accuracy, property, accessibility, and effects on quality of life. These issues are explored in the context of simulation models, databases, geographic information systems and artificial intelligence programs, especially expert systems. New approaches to system development place a much higher emphasis on the effects of system deployment within a complex human environment. Software design decisions often depend on more than one ethical issue, possibly conflicting, where the appropriate ethical choice is not always clear cut. Professional codes of ethics do little to change peoples' behavior; rather, incentives for using an ethical approach to software development may lie in significantly increased likelihood of system success.

Verstegen, J. A. A. M. and R. B. M. Huirne (2001). "The impact of farm management on value of management information systems." Comput electron agric 30(1/3): 51-69.
The value of management information systems (MISs) arises from improved managerial decision making and, therefore, will vary from farm to farm. Insight into this variation will be of use not only to farmers who consider (new) MIS investments, but also to companies that design and market MISs. In this study, the impact of farm management on the value of sow-herd MISs is investigated. Within the same research population, farm management is assessed with two conceptually different classification approaches - the sociological 'style of farming' approach and the farm-economic 'management level' approach. Management levels of sow farmers turned out to be positively correlated with MIS value (r = 0.35, P = 0.02). Although farmers with high management levels tend to be better informed anyway than farmers with low management levels, they get more added value from MISs.

Vieux, B. E. (2001). Distributed hydrologic modeling using GIS. Dordrecht ; Boston, Kluwer Academic Publishers, c2001. xvi, 293 p. : ill., maps.

Wang, M. (2001). "Possible adoption of precision agriculture for developing countries at the threshold of the new millennium." Comput electron agric 30(1/3): 45-50.
The concept of precision agriculture, based on information technology, is becoming an attractive idea for managing natural resources and realizing modern sustainable agricultural development. It is bringing agriculture into the digital and information age. The practice has smoothly extended into some developing countries. The basic principle of managing soil and crop variability within a field is certainly not new. It was named 'intensive and meticulous cultivation' by the Chinese people and has been long regarded as the cream of Chinese conventional agriculture. Toward the new millennium, China is preparing to follow the experience of the developed world and is starting to investigate the new technology. This paper considers the possible adoption of precision agriculture for developing countries and ideas in conducting the practice in China.

Whitney, J. D., Q. Ling, et al. (2001). "A citrus harvesting labor tracking and yield mapping system." Appl eng agric 17(2): 121-125.
A labor tracking and yield mapping system for manual citrus harvesting was developed and evaluated in two commercial harvesting operations in Florida. The system consisted of button recognition and barcode units, integrated with a differential global positioning system (DGPS) unit mounted on a truck, which was used to handle fruit collection containers (tub or bin) in the citrus grove. When the truck operator stopped to load each full tub or bin, the button and barcode of the harvester who filled the container was activated. This action recorded the number or name assigned to the harvester and the DGPS location of the container. The button unit was more reliable and was designed with an audible (alarm) and a visible (light) feedback to provide the truck operator verification of the recorded information. The system tallied the number of containers each harvester had harvested for the day and allowed the entry of other information pertinent to the harvesting operation. The DGPS data were used to map the yields with ArcView software. Field tests showed the labor tracking system was reliable and user friendly.

Whitney, J. D., Q. Ling, et al. (2001). "A DGPS yield monitoring system for Florida citrus." Appl eng agric 17(2): 115-119.
A yield monitoring system was developed based on a differential global positioning system (DGPS) and three fruit weighing systems. The DGPS unit eliminated post processing of the data and provided accurate location of fruit containers used in conventional manual harvesting. Three DGPS units did not vary significantly when comparing position accuracy. The weighing systems consisted of a pressure transducer mounted in the pressure line of the truck bed lifting cylinder, a system with four load cells under the four corners of the truck bed, and a single load cell in the loader boom. On trailer loads of fruit, the most to least accurate system was the lift cylinder (approximately 1% error), the loader boom (<2% error), and the load cells (approximately 5% error). On individual pallet bin loads of fruit, however, the coefficients of variation for the lift cylinder, loader boom, and load cells were 15, 6, and 25%, respectively.

Wu, B. M., A. H. C. v. Bruggen, et al. (2001). "Spatial analysis of lettuce downy mildew using geostatistics and geographic information systems." Phytopathology 91(2): 134-142.
The epidemiology of lettuce downy mildew has been investigated extensively in coastal California. However, the spatial patterns of the disease and the distance that Bremia lactucae spores can be transported have not been determined. During 1995 to 1998, we conducted several field- and valley-scale surveys to determine spatial patterns of this disease in the Salinas valley. Geostatistical analyses of the survey data at both scales showed that the influence range of downy mildew incidence at one location on incidence at other locations was between 80 and 3,000 m. A linear relationship was detected between semivariance and lag distance at the field scale, although no single statistical model could fit the semivariograms at the valley scale. Spatial interpolation by the inverse distance weighting method with a power of 2 resulted in plausible estimates of incidence throughout the valley. Cluster analysis in geographic information systems on the interpolated disease incidence from different dates demonstrated that the Salinas valley could be divided into two areas, north and south of Salinas City, with high and low disease pressure, respectively. Seasonal and spatial trends along the valley suggested that the distinction between the downy mildew conducive and nonconducive areas might be determined by environmental factors.

Sirjacobs, D., B. Hanquet, et al. (2002). "On-line soil mechanical resistance mapping and correlation with soil physical properties for precision agriculture." Soil tillage res 64(3/4): 231-242.

Timmermann, C., R. Gerhards, et al. (2002). "Analysis of the yield and weed distribution in arable fields in a Geographic Information Systems (GIS)." J agron crop sci 188(1): 34-42.