There’s still plenty time to apply nitrogen (N) to wheat in the eastern Midwest, says Edwin Lentz, Ohio State University (OSU) agronomist. He says N should be applied between green-up and beginning stem elongation. OSU research has shown that yields are not affected by delayed N 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 the first node visible of early stem elongation compared to initial green-up. Yields dropped 10-15% when a single application was delayed to early boot stage.
“At this time, we would recommend producers apply N as soon as field conditions allow application equipment,” says Lentz. “Since we are applying N between initial green-up and early stem elongation, any N source would be appropriate, so selection should be based on cost and availability.”
OSU 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,” says Lentz. “Thus, a realistic yield potential is needed to determine the optimum N 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% 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,” says Lentz, discussing wheat following beans. “Generally, we would recommend that you subtract from the total (spring N) any fall-applied N up to 20 lbs./acre.”
Based on the equation above and deducting 20 lbs. from a fall application, OSU recommends a spring application of 110 lbs. N/acre for a yield potential of 100 bu.; 90 for 90 bu. potential; 70 for a 80-bu. and 40 for a 60-bu potential. Since green-up has started across the region, price should be the main factor in selecting an N source. Volatilization losses should still be minimal for urea-based fertilizers at this time. Potential loss of N from 28% solution may be furthered reduced by applying in a band.