Late-season Irrigation Decisions More Difficult This Year

This year’s record rainfall across parts of the Midwest could make it more difficult for grain producers to determine a late-season irrigation strategy, a Purdue and Michigan State Extension irrigation specialist says.

Turning off the tap too early could reduce yield, but applying too much water to flood-damaged corn and soybean fields would be a waste of time, energy and money, said Lyndon Kelley.

“Late-August, early-September conditions in most years alleviate late-season irrigation scheduling questions,” Kelley said. “The typical crop water use drops as average rainfall increases.”

But in some flooded areas, crop development has been delayed, meaning the plants require more water than they normally would this late in the year.

“Often, the delayed portions of the fields have low yield potential for reasons other than lack of water,” Kelley said. “If those areas account for less than a quarter of the irrigated area, producers shouldn’t worry about additional applications.”

By mid-August, damp soybean fields could be at greater risk for developing white mold. Producers should spray the crop as few times as possible yet maintain at least 50 percent of the available soil water holding capacity until most pods turn yellow, Kelley says.

He advises applying as much as an inch of water at a time and allowing as much drying time as possible between applications. Limiting the number of applications helps to reduce the risk of a white mold outbreak, he said.

Plants with Soybean Sudden Death Syndrome generally have weaker root systems and a harder time taking in water, Kelley said. Producers should make sure the soil in the top 12 inches of the rooting area has higher moisture content.

Monitoring crop and soil conditions is especially important to ensure that the plants are getting the right amount of water, Kelley said.

Typically, soybean plants showing their first yellow pod need about one-tenth of an inch of water on a day when temperatures are in the mid-80s Fahrenheit, with corn at dent stage requiring slightly more.

Both Purdue and Michigan State Extension services publish real-time data on the Web, showing how much water crops require each day. The Purdue I-Climate website is available at Michigan State’s Enviro-Weather service is at

To monitor soil conditions, producers should use an auger probe to take a sample from 12 inches below the root zone. At that depth, the soil should form a loose ball, indicating the presence of moisture.

Soils that form a tight ball show an even higher level of moisture that could sustain the plant for at least a few days.

Corn producers trying to maintain test weight in dry, late-summer conditions should maintain about 50 percent of the available soil water holding capacity until the crop reaches black layer, Kelley said.

Source: Purdue University 

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