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Declining groundwater levels in the Great Plains are forcing farmers in this region to alter their irrigation strategies in order to maintain economic returns sufficient for sustainability. Outlined below are three common limited water situations with respect to a 126-acre standard pivot:
Low capacity: Well capacity of 350 gallons per minute (gpm) or less.
Allocated water: Average annual allocation of 12 inches or less with a well that has adequate capacity (more than 350 gpm) depending upon the year.
Low capacity plus allocated water: Average annual allocation of 12 inches or less with a less than 350 gpm well.
A good strategy when well capacities are limited is to use cropping practices that will require fewer irrigated acres at any one point during the growing season. This could mean devoting a portion of the field to dryland cropping or splitting the field between crops that have different water timing needs such as corn and wheat. For example, peak water demand for wheat is in May and June while corn and soybean require the most water in July and August.
Table 1 can be used to determine if your irrigation system can keep up with crop demands throughout the season. Compare the approximated daily and weekly application rates corresponding to your irrigation system’s capacity with the historical or actual crop water use rates for your field to determine when crop water needs will exceed the irrigation capacity. For example, a 350 gpm well on a 126-acre pivot can apply 0.15 inches of water per day and 1.0 inch per week. Crop water use rates may easily exceed this irrigation capacity during the reproductive stages (Table 2). If stored soil moisture is not adequate during this peak water demand period, water stress and yield losses could occur. In this situation, a farmer could choose to irrigate fewer acres. This 350 gpm well could irrigate 62 acres at an application rate of 0.30 inches per day and more closely meet peak crop demands.
The use of crop rotation is a common strategy for water conservation in limited irrigation systems. Rotating crops with high and low water needs can allow farmers to reserve irrigation for the high water needs crop, such as corn and soybean, and conserve water on crops that need less water, such as winter wheat. For example, if the annual irrigation allowance is 10 inches, a farmer could use a corn-wheat rotation where the wheat receives 5 inches in one season reserving a total of 15 inches of irrigation for the corn crop the following season.
Farmers can impose some water stress during the vegetative stages of corn and soybean without sacrificing yield. However, water stress at the reproductive stages can have a substantial impact on yield potential. Research studies have shown that irrigation can be withheld until approximately two weeks prior to tassel for corn and full flowering (R2) or early podding (R3) for soybean without incurring yield penalties.1,2,3 This type of irrigation strategy will require:
Genuity® DroughtGard® Hybrids corn products are part of a systems approach to drought mitigation combining top-yielding germplasm selected for its drought-tolerant characteristics, the inclusion of a drought-tolerant biotechnology trait, and agronomic best management practice recommendations. The systems approach is designed to help farmers manage risk and minimize yield loss when drought stress occurs. In yield trials from 2012-2015, DroughtGard Hybrids corn products have demonstrated a 5 bu/acre advantage over other corn products during severe drought conditions and in optimal growing conditions.
A technique used in the southern Great Plains when well capacity is insufficient to fully meet crop requirements during peak water needs is to irrigate before planting a crop. This provides a relatively full profile before the crop is planted, which helps to buffer the crop from water stress later in the season. This technique may not be suited for farmers with allocated water as pre-season irrigation uses a portion of the allocation to fill the profile, which could have been filled by precipitation. Pre-season irrigation works well on silt loam soils with high water holding capacities, but there is little advantage with this technique on sandy soils with low water holding capacity.