The goal of irrigation management is to use water in the most profitable way at sustainable production levels. For production agriculture this generally means supplementing precipitation with irrigation.
In recent years we have seen declines in groundwater levels, almost statewide. Much of the State of Nebraska is considered fully or over-appropriated. This means that in those over-appropriated areas there will be no new development of irrigated acres.
Some Natural Resources Districts have established pumping restrictions for irrigation water. Increases in fuel prices means that pumping extra irrigation water increases irrigation expenses without increasing income.
High nitrate levels have been found in many areas of the state. Nitrates in drinking water can be attributed, in part, to over-application of nitrogen fertilizer and/or over- irrigation.
All of these factors indicate that irrigators should be scheduling their irrigation applications to make maximum use of precipitation and reduce excess use of irrigation water.
Irrigation scheduling needs to begin with a discussion on soil and soil water. This is the basis of irrigation scheduling.
Coarse soils, such as sands and gravels, have relatively large pores. However the number of pores is small when compared to a finer textured soil. Fine soils, like clays or clay loams, have relatively small pores. Having many small pores means that a fine textured soil can hold more water than a coarse textured soil.
Coarse sandy soils can have roughly 0.5 inches of available water per foot of soil depth. On the other hand, silt loam soils have roughly 2 inches of available water per foot of depth. Crops can use about half of the available water without any yield reduction. With the large range of available water for different soil types, it becomes clear that a better understanding of soil water and soil physical properties is needed before fine tuning an irrigation schedule.
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.
- Click on 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. Go to Table 1 >>
- If you normally pump more than the average gross amount, you might consider a different method of scheduling your irrigations.
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:
- Reduce Need for Irrigation by Maintaining Crop Residue and Reducing Soil Tillage
- Calculator: Dollar savings from irrigating less (.xls)
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.
Ag Irrigation Management Publications from UNL Extension
Irrigation Scheduling: Checkbook Method (PDF 9 pgs, 696KB)
The checkbook method considers rain and irrigation as deposits, and crop water use as withdrawls.