On‐Farm Evaluation of Winter Wheat Yield Response to Residual Soil Nitrate‐N in North China Plain

Abstract

High soil nitrate‐N accumulation has been observed in North China Plain (NCP), but it was seldom considered as a N source in N management due to the lack of data on crop response to soil nitrate‐N accumulation. A total of 124 on‐farm N‐response experiments were conducted from 2003 to 2006 in seven key winter wheat (Triticum aestivum L.) production regions of NCP to evaluate wheat yield response to residual soil nitrate‐N. High soil nitrate‐N accumulation (≥172 kg N ha−1 in 90 cm soil depth) was observed during wheat growing season. Compared with 165 nitrate‐N ha−1 in 0 to 90 soil layer before sowing, added fertilizer N did not increase wheat yield under 262 kg nitrate‐N ha−1 condition, but increased residual nitrate‐N and N losses and reduced recovery N efficiency (P < 0.05). Wheat yield response to residual soil nitrate‐N could be fitted by a linear plus plateau model, and calculated minimum soil nitrate‐N content for maximum grain yield was 211 kg N ha−1 (R2 = 0.31) before sowing across all 223 zero‐N plots in 124 sites. When two growth periods (before and after shooting stage) were analyzed separately, the coefficient of determination between yield and soil nitrate‐N increased significantly. We conclude that winter wheat yield response to added N fertilizer was unlikely if soil nitrate‐N content exceeded 72 (0–30 cm soil depth) and 175 kg N ha−1 (0–90 cm soil depth) before sowing and shooting stage, respectively. According to these thresholds, 55% and 37% of farmer's fields did not need to apply N fertilizer before sowing and at shooting stage, respectively.