The Upper Midwest has received higher-than-average rainfall over the past few weeks, causing flooding and ponding in many corn fields. John Sawyer, professor of agronomy at Iowa State University, says that wet soils in June are more conducive to nitrate loss, reminding growers that corn plants “do not respond well to saturated soils, and therefore can express symptoms similar to N deficiency when they really are showing excess water stress.”
Growers can calculate nitrogen loss estimates to offer guidance for supplemental nitrogen applications, Sawyer says.
To estimate N loss, the first step is to estimate the amount of ammonium converted to nitrate-N. By now, one could assume late fall anhydrous ammonia and manure ammonium to be nearly converted to nitrate, and with early April preplant N applications a majority converted to nitrate. Less conversion to nitrate would occur with use of a nitrification inhibitor. Recent ammonium applications (within the last two weeks) would still be predominantly in the ammonium form, especially for anhydrous ammonia. Recent application of nitrate-containing fertilizers would result in more nitrate being present. Urea-ammonium nitrate solutions (28 or 32 percent UAN) contain one-quarter nitrate-N, and nitrify more rapidly. The second step is to estimate the percentage of nitrate-N loss as described in research from University of Illinois. The amount of nitrogen loss is calculated from these two estimates.
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