Grain yields in relation to N requirement: Optimizing nitrogen management for spring maize grown in China

The overestimation of nitrogen (N) uptake requirement under a high-yield cropping system with maize (Zen mays L.) has been a driving force in the overuse of N fertilization and environmental pollution in China. A database comprising 1246 measurements collected between 2005 and 2009 from 105 on-farm and station experiments conducted in the spring maize domains of the Northeast. Northwest of China and the North China Plain, was used to evaluate N uptake requirement in relation to grain yield. Field experiments with different maize cultivars and N management forms were also carried out to assess this relationship. Across all the sites, maize yield averaged 11.1 Mg ha(-1) which was more than twice that of the national maize grain yield average of China of 5.3 Mg ha(-1) and the world average of 4.5 Mg ha(-1). Nitrogen uptake requirement per Mg grain yield averaged 17.4 kg. Considering 6 ranges of grain yield (<7.5 Mg ha(-1), 7.5-9 Mg ha(-1), 9-10.5 Mg ha(-1), 10.5-12 Mg ha(-1), 12-13.5 Mg ha(-1) and >13.5 Mg ha(-1)), N uptake requirements per Mg grain yield were 19.8, 18.1, 17.4, 17.1, 17.0 and 16.9 kg respectively. This decreasing N uptake requirement per Mg grain yield with increasing grain yield was attributed to increasing harvest index (HI) and the diluting effects of declining grain and straw N concentrations. Grain yield increased with year of cultivar release from the 1950s to the 2000s. with N uptake requirement per Mg grain yield decreasing because of declining grain and straw N concentrations. Compared with the current commercial hybrid (ZD958), the lower N uptake requirement per Mg grain yield of the N-efficient hybrid of XY335 was attributed to a lower straw N concentration while maintaining a similarly high grain yield and grain N concentration. In neither of the years was there any evidence of leaf senescence in either optimal N rate (N-opt) or excessive N rate (N-over) and there was no significant difference between N uptake of these two treatments. This indicated that excessive N application could not delay leaf senescence to sustain further grain yield increase. (C) 2012 Elsevier B.V. All rights reserved.