Effects of nitrogen amount and fertilization patterns on crop yield and nitrogen use efficiency on the North China Plain

Appropriate fertilization is an important component for ensuring high crop yields and avoiding the disadvantages of non-point source pollution. We used the North China Plain as the study area and seven long-term experiments to investigate how different nitrogen application rates and fertilization modes (no fertilizer CK, fertilizer NPK, organic fertilizer M, organic-inorganic combined application NPKM) would affect crop yield and the efficient use of nitrogen. We found that there was a parabolic trend between crop yield and fertilization amount. The highest crop yield appeared in the combined application of organic and inorganic fertilizers and different fertilization modes affected crop yield. We found no significant difference between NPKM and NPK treatments for wheat yield, with both higher than with M and CK treatments. For maize crops, there was no significant difference in crop yield between NPKM, NPK and M although they had significantly higher yields than with CK treatment. The nitrogen utilization rate decreased with higher nitrogen application and fertilization modes had certain effects on nitrogen utilization rates. We found no significant difference in nitrogen use efficiency between NPKM and NPK treatment for wheat, but they were higher than with M treatment. There was no significant difference in nitrogen use efficiency between NPKM, NPK and M for maize. This comprehensive analysis of the effects of nitrogen application rate and fertilizer replacement ratio on wheat yield showed that, in the North China Plain, there was great potential to replace chemical fertilizers with organic fertilizers. This replacement would not significantly decrease crop yields, and possibly led to higher yields than with purified fertilizer. However, in order to avoid a significant decrease in crop yields, total N input should be determined when replacing chemical fertilizer with organic fertilizer.