Assess Nitrogen Loss After Heavy Rains

Nitrogen (N) applied either last fall or this spring may wash away in areas experiencing substantial rainfall. After excessive rains, growers need to reassess nitrogen levels to ensure optimal yields at harvest, say Pioneer experts.

Pioneer agronomists suggest growers walk fields to estimate N loss, looking for lighter green or yellowing corn. To estimate losses, growers can rely on soil testing, chlorophyll meters or aerial photographs. Although they don't provide exact quantities, aerial images help determine the extent of loss across a whole field. Aerial images may work best if corn is waist high or taller.

Growers have options to correct N deficiencies. Once corn is too tall for N application machinery, rescue options are limited but not impossible. One of the best options is to dribble nitrogen between the rows with high-clearance equipment or aerial application. Another option is to broadcast dry urea. Broadcasting a urea-ammonium nitrate (UAN) solution on taller corn can cause substantial yield loss due to severe leaf burn. Between-row applications are safer. These applications are most effective prior to silking, the R1 stage.

Some growers may wonder if a late, or "rescue," application of N is worth the extra cost and effort. Research studies show positive responses to late N application. Corn typically uptakes nearly 40 percent of its total nitrogen needs after tasseling. Correcting N deficiencies prior to tasseling ensures plants meet their N needs throughout grain fill.

With warmer temperatures and significant amounts of rain, even growers who used N stabilizers may lose N. Stabilizers help delay the conversion of ammonium to nitrate. Corn standing in water for several days or saturated ground loses N to denitrification.