Abstract: Application of nitrogen fertilizers is one of the most important measures to increase crop yields. Lankao’aizao 8 is a famous large-spike wheat (Triticum aestivum L.) cultivar planted widely in North China. To optimize the nitrogen application in Lankao’aizao 8 for the integrated purposes of yield, economic benefit, and environmental influence, a field experiment was carried out at Henan Agricultural University in 2005—2006 growth seasons. The nitrogen fertilizer treatments were arranged with application rates of 0 (N1), 90 (N2), 180 (N3), and 360 kg N ha^-1 (N4) in the randomized block design with three replicates, respectively. A half of the nitrogen fertilizer was applied before sowing as basic fertilizer together with 150 kg P₂O₅ ha^-1 and 150 kg K₂O ha^-1 and the other a half topdressed at jointing stage. Time-course measurements were taken on plant dry weight, nitrogen content, grain protein content, soil mineral nitrogen (N min) content during the experiment. The results showed that the grain yield and protein content increased with increasing nitrogen application amount, but the grain yield at N4 level (8 299.45 kg ha^-1) was lower than that at N3 level (8 602.92 kg ha^-1) though there was no significant difference. The N accumulation in shoots increased constantly with more nitrogen fertilizer applied. The N uptake in plants during jointing to heading accounted for 45.6%, 53.0%, and 49.7% of whole uptake amount in N2, N3, and N4 treatments, respectively, indicating wheat plants are sensitive to nitrogen from jointing to heading stages. The analysis on N balance further indicated that the unutilized nitrogen by the current crop mainly lost in forms of residual Nmin in soil and apparent N, which increased accordingly with more nitrogen applications. Considering grain yield and protein content, economic benefit, and ecological effect synthetically, the proper amount of nitrogen fertilizer for Lankao’aizao 8 in production in areas similar to the experimental condition is 202–239 kg ha^-1 calculated by the Marginal Revenue Analysis and the Coase theory of environmental economics. Accordingly, the expected grain yield and protein content are 8 628–8 680 kg ha^-1 and 14.6–14.8% under the current cultivation techniques, respectively.

Key words: Winter wheat, Yield, N balance, Nitrogen application rate