Availability of 15N‐Labeled Nitrogen in Fertilizer and in Wheat Straw to Wheat in Tilled and No‐Till Soil

Abstract

AbstractIn a field study, wheat (Triticum aestivum L.) was grown in microplots under conventional tillage and no‐till seedings to compare availability of fertilizer nitrogen for two consecutive crops. The 15N‐labeled ammonium sulfate was surface‐applied in May 1980 to a spring wheat crop which utilized 25 to 40% of the fertilizer N, with the highest uptake occurring on no‐till. There was no difference in dry matter production between tillage methods. A winter wheat crop was then grown in the same microplots to assess the availability of the residual labeled fertilizer N, and in new microplots which were treated with the spring wheat straw containing 5.29 atom % 15N and 1.20% total N to assess the availability of straw N. Approximately 9% of the wheat straw N was taken up by the 1980 to 1981 winter wheat crop, while an average of 6% of the residual fertilizer N was utilized. Winter wheat dry matter production was highest on no‐till receiving 168 kg N/ha, but no difference was found between the effects of tillage methods on the availability of straw N or on the uptake of residual fertilizer N. Therefore, decreased wheat production on no‐till in the Pacific Northwest would not likely result from poorer crop utilization of fertilizer N under no‐till than under conventional tillage. Overall low crop N‐use efficiencies of the surface‐applied fertilizer N were likely due to immobilization and denitrification.