As summer winds down and crops approach maturity, the time is nearing to schedule your last irrigation of the season. According to Nebraska Extension’s “Irrigation and Nitrogen Management” handbook, “the application of a late irrigation when irrigation is not needed can reduce the storage for offseason precipitation by 1 to 3 inches.” As a producer, the best-case scenario is for your crop to deplete the soil moisture as much as possible so there is room available for the storage of offseason precipitation. If your soil profile does not have the storage available, then offseason precipitation can lead to more leaching of nitrates. Failing to utilize offseason moisture will also increase your pumping and fertilizer costs for the following year.
To schedule your final irrigation for the season, determine a prediction of the water your crop will need to reach maturity and know the amount of moisture still available in the root zone of your field. For example, if you have a corn crop that is beginning dent, it will need approximately 5 more inches to reach maturity. If the moisture available in the root zone is less than what is required to reach maturity, you would schedule a final irrigation that meets the need. It's important to remember that, even if there are hot windy days after your last irrigation, the plant will still use the same amount of water to reach maturity, it will just finish out quicker. Information on your soil moisture is a key to determining how much water will be needed to finish your crop. If you do not already, consider getting sensors in at least one of your fields to get the information you need.
If you want to keep tabs on how crops are using water in the area, check the weekly Crop Water Use Report on the Lower Loup NRD website. The report gives average daily water use data for corn, soybeans, and potatoes with a series of easy-to-read graphs. Each graph displays the water use of the crop at four different growth stages so they can be used by producers no matter when they planted. Visit LLNRD.org, go to the Resources tab, and click on Crop Water Use.