On-farm evaluation of the improved soil Nmin-based nitrogen management for summer maize in North China Plain

The improved soil N-min-based N management is a promising approach to precision N management, which determines the optimum side-dress N rates based on N target values and measured soil nitrate N content in the root soil layer at different growth stages. A total of 148 on-farm N-response experiments, in seven key summer maize (Zea mays L.) production regions of North China Plain (NCP) from 2003 to 2005, were conducted to evaluate the N-min-based N management compared to traditional farmer's N practices. The recommended N rates based on the improved soil N-min method were not significantly different (<= 31 kg N ha(-1)) from those determined by yield response curves (n = 13). The average N rate determined with the soil N-min method (157 kg N ha(-1)) was significantly lower than farmer's practice (263 kg N ha(-1)), while maize grain yield was 0.4 Mg ha(-1) higher than farmer's N practice (8-5 Mg ha(-1)) across all sites (n = 148). As a result, the improved soil N-min-based N management significantly increased net economic gains by $202 ha(-1), reduced residual nitrate N content and N losses by 44 kg N ha(-1) and 65 kg N ha(-1), respectively, and improved recovery N efficiency, agronomic N efficiency and N partial factor productivity by 16%, 6 kg kg(-1) and 36 kg kg(-1), respectively, compared with farmer's N practice. We conclude that the improved soil Nmin-based N management can be applied for summer maize production in NCP for improved N use efficiency and reduced environmental contamination.