Em4885 irrigation management practices to protect ground water

4 CHAPTER
Using the previous example, assume the following:
• desired 23-hour sets (1 hour to change pipe positions)
• overall application efficiency of 75%
• application rate of .2 inch/hour
Now, solving for the soil water depletion at the time of irrigation:
SWD = SET TIME x AE x AR
= 24 x .75 x .2
= 3.6 inches
Thus, the farmer would wait until the soil water depletion was 3.6 inches before putting on
the 23-hour set. This assumes that the 3.6-inch soil water depletion will not adversely
affect crop development.
There are other methods for determining a strategy for center pivots and micro-irrigation
systems. WSU Cooperative Extension publication EB1305, Sprinkler Irrigation -
Application Rates and Depths, contains a detailed discussion on planning irrigations
with sprinkle systems.
4. React to the results - the initial irrigation sets should be monitored closely to see if the
strategy chosen is appropriate. The grower might have to react to unforseen circumstances.
5. Maintain records - most growers keep detailed records of farming operations and irrigation
management should be no different. The soil water deficit at irrigation, the condition of the
furrow, border strip, or field surface, the climate, the strategy used, and results should
all be noted.
SCS National Practice 449 addresses general irrigation water management while Practice
610 covers leaching for salt control.
IP 2.01.07 - Use Two Irrigation Systems in Special Situations (sprinklers for
pre-irrigations then furrows; portable gated pipe to reduce furrow lengths
for pre-irrigations; sprinklers to germinate crops irrigated by micro-irrigation;
over-tree sprinkler for cooling/frost control with undertree for irrigation)
Objective
Ensure that an appropriate irrigation system type is used throughout the season.
An appropriate system type will allow the highest application efficiency possible
consistent with overall farm economics.
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