Watch Corn Water Use Over the Next Few Weeks
Chad Lee, University of Kentucky
The current heat wave is expected to last until the end of June. There are some low chances of rain scattered in the forecasts. We need to start watching water use in corn across the state. The next two weeks could provide us with some strong indicators on expected corn yields this fall.
Corn water use increases from emergence to about V15 where it peaks until about R2 (blister stage) and then starts to drop off after that. At peak water demand, corn likely uses about 0.25 to 0.33 inches per day in our region. Air temperature, humidity and cloud cover all affect how much water is lost each day. Corn that is pollinating is the most sensitive to water stress.
Last year, about 20% of the Kentucky corn crop was pollinating by July 1. The 5-year average is closer to 35% of the corn crop pollinating by July 1. Corn planting was delayed a bit this year, but it is reasonable for us to assume that at least 15% or more of the corn crop will start pollinating in the next 10 days.
No-till and strip-till fields may be at an advantage over the next two weeks. Before corn gets tall enough to cover the rows, some water loss occurs from the soil. This evaporation is greater on tilled fields. Fields in no-till, strip till, and/or with excellent residue cover usually have less evaporation right now. Once the corn crop covers the rows, nearly all water loss is from the corn plants. That type of loss is transpiration. At this point, residue cover on the soil is less important than it was when corn plants were smaller. Deep roots are extremely important for the corn crop from here to the physiological maturity. Deep roots can access more water than corn plants with stunted roots from sidewall compaction or subsurface compaction. We may find out which fields were planted “just a bit too wet” this spring.
Farmers who can irrigate should be watching soil moisture and crop growth stages closely. Irrigation may need to begin in some areas where corn is farthest along. Irrigation should not overwater the field. Both dry soils and saturated soils can hurt pollinating corn. Soil moisture sensors can help greatly in targeting proper irrigation amounts.
Most farms do not have irrigation. In these fields, the heat and possible water stress are a matter of timing. Corn plants closest to pollination are likely at greatest risk over the next two weeks. Corn plants at earlier growth stages are a little more resilient. If irrigation is not an option, all we can do is watch the fields closely and monitor pollination success in a few weeks.