Effect of Nitrogen Management on Yield and Water Use Efficiency of Rainfed Wheat and Maize in Northwest China1

ABSTRACTA field experiment with four treatments and four replicates in a randomized complete block design was conducted at the Changwu Experimental Station in Changwu County, Shaanxi Province, of Northwest China from 1998 to 2002. The local cropping sequence of wheat, wheat-beans, maize, and wheat over the 4-year period was adopted. A micro-plot study using 15N-labelled fertilizer was carried out to determine the fate of applied N fertilizer in the first year. When N fertilizer was applied wheat (years 1, 2 and 4) and maize (year 3) grain yield increased significantly (P < 0.05) (> 30%), with no significant yield differences in normal rainfall years (Years 1, 2 and 3) for N application at the commonly application rate and at 2/3 of this rate. Grain yield of wheat varied greatly between years, mainly due to variation in annual rainfall. Results of 15N studies on wheat showed that plants recovered 36.6%–38.4% of the N applied, the N remained in soil (0–40 cm) ranged from 29.2% to 33.6%, and unaccounted-for N was 29.5%–34.2%. The following crop (wheat) recovered 2.1%–2.8% of the residual N from N applied to the previous wheat crop with recovery generally decreasing in the subsequent three crops (beans, maize and wheat).