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 (Zea 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 (Nopt) or excessive N rate (Nover) 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.

► We analyze maize yield-N uptake requirement relations.
► N uptake requirements per Mg yield decreased with increasing yield because of the increasing HI and declining grain and straw N concentrations.
► N uptake requirements decreased with cultivars released from 1950s until now mainly due to declining grain N concentrations.
► Overuse N fertilizer could not delay leaf senescence and prolong photosynthetic activity.