Precipitation Patterns

Another major factor in irrigation scheduling is making use of precipitation, both during the growing season and in the off season. Shown below is a map detailing the average net irrigation requirement for corn for the State of Nebraska.

The net irrigation requirement is based on precipitation patterns and soils. In wet years less water is needed and in dry years more water will be needed.

View the map below to see the net irrigation requirement for your area.
Divide net irrigation requirement by the application efficiency of your irrigation system (Table 1). The result is the average gross amount of irrigation you need to apply in an average year.
If you normally pump more than the average gross amount, you might consider a different method of scheduling your irrigations.

Table 1 - Managing Irrigation Applications
System		Overall Efficiency, %
Furrow Irrigation	Every Row	40-75
	With Surge Valve	60-85
	With Reuse	55-90
	Siphon Tube	40-75
	Alternate Row	60-85
Sprinkler Irrigation	Hand Move	60-80
	Solid Set	60-85
	Traveler	55-75
	High Pressure Impact	70-80
	Low Pressure Impact	75-85
	Low Pressure Spray	70-90
	Low Pressure Bubble	60-95
Drip Irrigation		70-95

Gross irrigation calculator (below) can help you determine the average gross amount of irrigation that you will need to apply in order to meet water demand of corn.

Download Calculator (.xls)

A way to significantly reduce irrigation requirements is to leave more crop residue on the field and practice less tillage. For more information:

In some areas where water restrictions are significant, deficit irrigation of crops may need to be practiced.

Under allocation most producers will not be able to pump the economical optimal amount of irrigation water. In addition to good irrigation management, producers may need to consider other water saving practices.