Irrigation
Water Management
Irrigation
Scheduling Basics
1-Car
Analogy
First Volkswagen's in the US
- This car has a 10 gallon gas tank
(+ some reserve -> you can use the whole 10 gallons).
- As you drive, you get 30 miles per gallon.
- You average 20 miles of driving per day.
1) How far can you
drive on a full tank before needing to refuel?
- 30 miles/gallon x 10 gallons/tank
= 300 miles/tank
2) If you follow
this practice, how many days between gas stops?
- 300 miles/tank ÷ 20
miles/day = 15 days/tank
3) If you refuel
10 days after fill-up, how much gas can you put in your tank without
it overflowing?
- 10 days driving x 20 miles/day
= 200 miles driven
- 200 miles driven ÷ 30
miles/gallon = 6-2/3 gallons used
4) Your room-mate,
who drives with a lead foot, only manages to get 25 miles per
gallon when borrowing your car. Your room-mate also drives 20
miles per day (when you are so benevolent as to make the car available).
How long can your room-mate go between fill-ups?
- 25 miles/gallon x 10 gallons/tank
= 250 miles/tank
- 250 miles/tank ÷ 20
miles/day = 12-1/2 days/tank
5) You get your car
fitted with a new gas tank that has a capacity of 12 gallons (+
some reserve -> you can use the whole 12 gallons). How many
days can you go between fill-ups?
- 30 miles/gallon x 12 gallons/tank
= 360 miles/tank
- 360 miles/tank ÷ 20
miles/day = 18 days/tank
What's
the analogy?
| car, fuel use |
==> |
soil-plant-water
system, water use |
| gas tank |
==> |
soil
moisture reservoir
+ soil type (texture)
+ root zone |
| miles/day ÷ miles/gallon = fuel
use (gallons/day) |
==> |
water
use (in/day) (ETc) |
| model of auto, driver, driving habits,
driving route all change fuel use |
==> |
crop,
time of season, weather all change water use |
| amount of fuel used |
==> |
soil
moisture depletion (SMD) |
| amount
of fuel to add when refueling |
==> |
soil
moisture depletion (SMD) at time of irrigation |
| amount
of fuel left |
==> |
soil
moisture content (SMC) |
| size
of fuel tank |
==> |
available
water holding capacity (AWHC) |
| maximum
fuel use allowed to maintain a reserve to prevent running out
of gas on the freeway |
==> |
maximum
allowed depletion
max SMD = AWHC x MAD |
| days
between refilings |
==> |
days
between irrigations |
|