On‐Farm Evaluation of the Improved Soil N_min–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 N min –based N management can be applied for summer maize production in NCP for improved N use efficiency and reduced environmental contamination.