When Should Minnesota Farmers Irrigate Again?

By Scout Nelson

Minnesota farmers are facing important irrigation decisions as corn and soybean crops move closer to maturity. Hot, dry conditions and limited rainfall have left some areas of the state with low soil moisture. As harvest approaches, growers are asking whether another round of irrigation is needed.

University of Minnesota guidance explained that the decision depends mainly on three factors: the amount of water remaining in the crop’s root zone, the current crop growth stage, and the amount of water the crop is expected to use before maturity.

Corn and soybeans can still need water during their later reproductive stages. Corn may lose yield when water stress reduces grain filling and kernel weight. Soybeans also need enough moisture during pod and seed development to support yield. Therefore, late-season irrigation can still be useful when crops have high water needs, and soil moisture is too low.

However, not every field needs additional water. Soil moisture can differ based on soil type, rainfall, root depth, and previous irrigation. Fields that receive timely rainfall may have more available water than nearby fields. Farmers can use soil moisture sensors, soil probes, and irrigation scheduling tools to check conditions before deciding.

The crop growth stage is also important. Corn at the beginning dent stage may have about 2 inches of water use remaining through maturity, while corn at half milk line may need about 0.8 inches. Soybean water needs can decline from about 2.9 inches at beginning seed to about 1.2 inches at full seed.

Farmers should also watch the short-term weather forecast. Applying too much water before rainfall can move water and nitrate below the active root zone. This risk becomes more important as crops near maturity and nitrogen uptake slows.

The best approach is to combine soil moisture information, crop growth stage, expected water use, and weather conditions. More irrigation is not always better late in the season. Careful planning can help farmers protect yield while avoiding unnecessary water use and costs.

Photo Credit: istock-laughingmango