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Ponded Fields Can Take Out Nitrogen, Crops

Ponded Fields Can Take Out Nitrogen, Crops
When in season, soybeans tend to hold on a little longer than corn.

Somewhere almost every year somebody deals with ponding and flooding after the crop is up. In 2013, Sullivan and Knox Counties bore the brunt of ponding and flooding, but it occurred in other areas that received heavy rains in June as well.

Two things happen. One, says Mike Earley, agronomist with Seed Consultants, Inc., is that nitrogen tends to take off. It either leaches down into the soil with the rain below where crop roots can get it, or denitrifies into the air as a gas and is lost. Bacteria in saturated soils and N in the nitrate form lead to losses.

Weather matters: These crops can survive ponded conditions longer if the temperatures in the soil and in the air are 60 degrees F or cooler.

The other issue is how long crops can remain under water and still survive. That varies by the amount of time the crop is submerged, which crop it is and the stage of growth of the crop, plus the weather conditions at the time, Earley says. He saw plenty of ponding in 2013 and watched how the crops reacted.

"Corn plants at V6 stage or younger are more at risk because the growing point is still near ground level," he says. "In general, young corn plants can survive two to four days covered with water.

"Part of it depends upon the weather. If the soil and air temperature are 60 degrees F or lower, the crop may hang on longer. However, if the sun is out and the temperature is 70 to 80 degrees, it bakes the crop under water and some plants may not survive even 24 hours."

Small soybeans can generally survive 48 to 96 hours under water, but may be able to survive longer if conditions are right, he notes. However, if the flooding and ponding is later in the season when soybeans are in the reproductive stage, yield losses will mount up quickly. If soybeans flood at the R1 stage, at the beginning of the reproductive phase, yield losses may be 1.5 to 2.3 bushels per day that the crop is submerged, he concludes.

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