Sat Nov 07 2009
With nitrogen accounting for 35-50 percent of the total fertilizer costs of growing winter wheat, growers should pay special attention to the amount and timing of the application. Spring nitrogen should be applied between greenup and beginning stem elongation (Feekes 6). Ohio State University research has shown that yields are not affected by delayed nitrogen until after early stem elongation (generally the end of April). Studies over the last five years have shown that yields were the same or slightly better when a single application occurred at Feekes 6 (first node visible of early stem elongation) compared to initial greenup. Since we are applying N between initial greenup and early stem elongation, any nitrogen source would be appropriate, so selection should be based on cost and availability.
Ohio State University still recommends the Tri-State Fertility Guide for N rates in wheat. This system relies on yield potential of a field. As a producer, you can greatly increase or reduce your N rate by changing the value for yield potential. Thus, a realistic yield potential is needed to determine the optimum nitrogen rate.
Once you have selected a value for yield potential, the recommendation may be based on the following equation for mineral soils, which have 1-5 percent organic matter and adequate drainage: N rate = 40 + [1.75 x (yield potential - 50)]
We do not give any credit for the previous soybean crop, since we do not know if that organic N source will be released soon enough for the wheat crop. Generally, we would recommend that you subtract from the total (spring N) any fall applied N up to 20 lb/A.
Based on the equation above and deducting 20 lb from a fall application, we would recommend a spring application of: 110 lb N /ac for a yield potential of 100 bu, 90 lb N/ac for 90 bu/ac; 70 lbs N/ac for a 80 bu/ac and 40 lb N /ac for a 60 bu/ac yield potential.
Volatilization losses of nitrogen should still be minimal for urea based fertilizers at this time. Potential loss of nitrogen from 28 percent solution may be furthered reduced by applying in a band (dribble bar).
(Bruce Clevenger is the agriculture and natural resouces educator at Ohio State University Extension, Defiance County. He can be reached at 419-782-4771, or clevenger.10@cfaes.osu.edu.)
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