Accumulation and Redistribution of Fertilizer Nitrogen‐15 in Soft Red Winter Wheat

Abstract

AbstractInformation is lacking on N accumulation in soft red winter wheat (Triticum aestivum L.) and the fate of residual fertilizer N in soil. The objectives of this study were to determine the uptake and redistribution of fertilizer and total N within the wheat plant as well as the amount and distribution of fertilizer N in the soil profile at wheat maturation. Urea‐15N was applied at the rate of 112 kg N ha−1 at tillering. Plant samples were taken at six growth stages and partitioned into top and bottom leaf blades, stem + leaf sheaths, and spikes, and analyzed for total and fertilizer N accumulation. Soil samples were taken at wheat harvest and analyzed for total N and fertilizer N recovery in inorganic, organic, and total N fractions. Nitrogen accumulation in the wheat plants increased until flag leaf emergence and then displayed no significant change during later growth stages or at maturity. Leaf blades and stem + leaf sheaths attained maximum N accumulation at flag leaf emergence and heading, respectively. Spikes continued to accumulate N from heading until maturity. Nitrogen loss from the leaf blades and stem + leaf sheaths exceeded N gain in the spikes. A maximum fertilizer N accumulation of 74.4% in the wheat plants was found by the flag leaf stage and then the fertilizer N accumulation steadily declined to only 46.7% by maturity. Fertilizer N accumulation for plant parts was similar to total N accumulation; however, significant fertilizer N losses occurred after flag leaf emergence. Fertilizer N recovered in the 0‐ to 100‐cm soil layer following harvest was only 11.6% of that applied and was mainly concentrated in the organic fraction of the top 10 cm of soil.