MSU Extension

Most irrigation systems were designed to supplement summer rainfall and do not have the long term capacity to keep up with drought condition crop water requirements. This can result in yield and quality reduction when water is restricted. The need for water is most critical now. Reducing irrigation to the level that is below basic crops water needs will jeopardize both the investment made on the applied water and purchased crop inputs. Corn exhibits the greatest yield reduction from drought conditions at pollination and the following two weeks.

Soybeans have little yield reduction in when drought conditions occur during the vegetative growth period as long as enough water is available for near normal plant growth. Adequate water is critical through blossom to prevent aborting of developing pods. Greatest yield advantage from irrigation is often achieved from R3 (beginning pod, one pod 3/16 inch long on one of the upper four nodes on the main stem having unrolled leaves) through R6 (full seed, one pod containing green seed that fills the pod cavity on one of the upper four nodes on the main stem having unrolled leaves. Water applied at R3 to R5 encourages flower and pod retention. This increases yield potential by increasing the number of seeds per acre. Irrigation water applied after R5 will primarily improve yields by increasing seed size.

What can you do as irrigators?

1. If your water supply becomes challenged; prioritize your irrigations to the greatest advantage. Limit irrigation to acreage that you can meet crops water needs, giving priority to the most valuable crop at it critical stages.
2. Consider rebuilding part of the soil reserve if your water supply allows after limited rainfall events. In fields where crops are showing soil moisture depletion like rolling corn or flipped soybean leaves consider building a reserve by irrigating in excess crop E.T. It may be possible to reduce water applications late in the growing season with minimal impact on yield
3. Maximize the percentage of irrigation water that enters the soil and is available to plant roots. Irrigation water applied at a rate faster than it can infiltrate into the soil can cause runoff. Even if the water does not leave the field it can create under and over irrigated spots. Walk the most venerable sites in your irrigated fields and identify problem areas. Venerable areas have the heaviest (finer textured) soils or most compacted areas. Look for areas where water is applied the fastest by the system, with a focus on near the last tower of a center pivot. If signs of runoff are present, reduce your irrigation application rate. For future years, consider changing the distribution system to one offering greater wetted areas.
4. Maximize application rates while avoiding runoff. Irrigation water that evaporates directly from the soil or foliage does not effectively meet the plants water needs. During drought condition as much 0.1 inches of each application is caught in foliage and soil upper surface where it evaporates directly to air. Bare soils may have one to two inches of topsoil that void root development due to excessive heat. This soil will hold 0.06 to 0.14 inches of irrigation from the plant for each application depending on the type of soil and presents crop residue. An irrigator applying a single one and a half inch of water instead of three 0.5- inch applications to a soil with a surface that holds 0.1 inches/ inch in the top inch of soil will have saved 0.2 inch of irrigation water.
5. Improving uniformity of the irrigation system allows all areas within the field to receive close to the same amount of water. Adjust end guns, repair leaks and sprinkler malfunctions to provide as uniform application as possible. Eliminating under- or over-irrigated portions of the coverage area allows closer management of water without jeopardizing yields. Recent Nebraska research shows minimal irrigation water saving from drop nozzles. These systems greatly increase the potential of irrigation water runoff (because water is applied to a smaller area) and can result in poor uniformity when plant height interferes with distribution pattern.
6. Verify your actual application by measuring system output over many locations, or better yet, a complete system evaluation. In testing on over 40 systems, it was not uncommon for the producer’s estimate of application to be 20 percent different than the tested application.
7. Plants grown on heavier soils will need as much water as plants in light sandier soils. The crops evapotranspiration needs are the same for the plant. The advantage of heavier soil is that it can store more water so additional water is carried into the summer and larger rainfall events in the summer are more effectively stored. Once the soil moisture is depleted the same amount of irrigation water must be applied to meet crop needs.
8. If water supply during drought is not adequate to run the entire system continuously, consider pumping for only part of each day thus allowing time to replenish the pumps draw down area or for ponds to recharge. Reduced pumping volumes may allow a continuously lower than normal pumping volume. Close down the supply line valve, shut off the pivot end gun or reduce big gun nozzle size to adjust the system’s application to a lower volume requirement.
9. Private ponds can often improve groundwater recharge by cleaning and expanding their area. Water temperature difference in the pond can be used as an indicator of the direction of recharge. A local excavator with irrigation pond digging experience is often the best resource in determining potential pond improvements. A recharge well is sometimes utilized to pump continuously at a low volume into existing pond to store water for irrigation. Since most existing irrigation ponds normally recharge themselves (they are connected to the aquifer), recharge wells are relatively ineffective as water is circulated back to the aquifer.
10. Problems have occurred when impoundments have been created in county drains including blowouts and damage to culverts crossings. Always consult the local drain commissioner when making changes in a public drain.
11. Irrigation scheduling can result in more effective use of the water.

For more information on avoiding irrigation runoff, test irrigation system uniformity or irrigation scheduling and the drought visit:

• Michigan State University (MSU) Extension’s Irrigation Resources page.

• MSU Extension’s Drought Resources