On-farm evaluation of the improved soil nmin–based nitrogen management for summer maize in North China plain
The improved soil Nmin–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 Nmin–based N management compared to traditional farmer's N practices. The recommended N rates based on the improved soil Nmin 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 Nmin 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 Nmin–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.