Change in Nitrogen Requirement with Increasing Grain Yield for Winter Wheat

Overestimates of N requirements have led to excessive N application and serious environmental pollution in intensively managed agricultural systems. A database comprising 1395 measurements was developed from 2000 to 2011 using 88 on‐farm and station experiments conducted in five key winter wheat ( Triticum aestivum L.) domains in northern China. The database was created to evaluate the relationship between aboveground N uptake and grain yield with different N treatments and to quantify N requirements per Mg grain at different grain yield levels. Across all sites, wheat grain yield ranged from 1.6 to 11.8 Mg ha −1 . The nitrogen requirement per megagram grain yield (N req. ) increased with N supply from 20.8 kg under the treatment without N fertilizer to 25.7 kg under the excess N treatment. For the optimal N fertilizer treatment, the average N req. was 24.3 kg and it declined with increasing grain yield. For the yield ranges between <4.5 and 6.0 to 7.5 Mg ha −1 , N req. decreased from 27.1 to 24.5 kg due to increasing harvest index (HI; from 0.39–0.46) and decreasing grain N concentration (from 2.41 to 2.21%). For the yield ranges between 6.0 to 7.5 and 9.0 to 10.5 Mg ha −1 , N req. decreased from 24.5 to 22.7 kg due to decreasing grain N concentration (from 2.21 to 2.00%). For the yield ranges between 9.0 to 10.5 and >10.5 Mg ha −1 , N req. changed little due to stability in grain N concentrations and HI. In conclusion, the N requirement of a crop was affected by both the amount of N supplied and the grain yield.