Irrigation Water Management

Irrigation Scheduling

4-Choice of Management Allowable Depletion (MAD)

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Situations Calling for Large MAD

• Hand move or wheel move sprinkler systems
  • With little hardware to cover many acres, these systems require a significant amount of time to get through their complete cycle and back to their beginning point again
• Furrows and border strips with long runs or sandy soils
  • These systems require a minimum amount of water just to get the water across the field
  • It's difficult to apply small amounts uniformly, and the larger application amounts are associated with longer irrigation intervals
• Specific plant requirements
  • Some plants need [moisture] stress at some point in their development, and this implies drying out, longer irrigation intervals and larger MADs
  • Almonds prior to harvesting - if tree bark is wet, shaker used to harvest almonds will damage tree trunk
  • citrus prior to bud formation
  • cotton - to promote set/growth of bolls rather than excessive vegetative growth
  • Grapes for wine, prior to harvest - some stress (up to 200 cb) can cause favorable effects on characteristics of grape juice
  • Some trees & vines prefer stress prior to wintering. The stress seems to "harden" the plant, and reduces liquid sap in trunks to avoid frost damage

Situations Calling for Small MAD

• Irrigation systems capable of frequent light applications
  • Microirrigation
  • Some sprinkler systems
    • Solid set
    • Permanent set
    • Center pivot
    • Linear/lateral move
    • LEPA
• Microirrigation requires frequent irrigations because only a portion of the soil volume is used
• Irrigation with saline water - salt damage can be reduced by keeping the soil very moist
• Shallow root zones - limit depletion to provide a safety buffer
• Uncertain water supply
• Specific plant requirements
  • Root crops like carrots, onions and potato need moist soil for proper shaping of root tubers
  • Strawberries are sensitive to moisture stress at all stages of growth
  • Some stone fruits (peaches, cherries) are sensitive to stress during fruit sizing
    • Stress hardens fruit skin
    • Moist soils after stress causes spurt of re-growth of fruit, splitting fruit
  • Corn is very sensitive to stress during its pollination stage