On-farm evaluation of an in-season nitrogen management strategy based on soil N_min test

Successful nitrogen (N) management requires better synchronization between crop N demand and N supply from all sources throughout crop growing season. An in-season N management strategy based on soil N_min test had been developed under experimental conditions, and more than half-N fertilizer could be saved without grain yield losses, compared with farmer's N management practices. The objective of this study was to evaluate this in-season N management strategy for winter wheat (Triticum aestivum L.) in different farmers' fields of North China Plain (NCP). A total of 121 on-farm N-response experiments (check with no N fertilizer, in-season N management based on soil N_min test, and farmer's practice) were conducted in seven key winter wheat production regions of NCP from 2003 to 2005. The average N rate determined with in-season N management strategy (128 kg N ha^-1) was significantly lower than farmer's practice (325 kg N ha^-1) without wheat grain yield losses. As a result, in-season N management strategy significantly increased economic gains by $144 ha^-1, reduced residual nitrate-N content in the top 90 cm soil layer and N losses by 81 and 118 kg N ha^-1, respectively (P < 0.05). Recovery N efficiency (REN), agronomic N use efficiency (AEN) and N partial factor productivity (PFPN) were significantly improved to 44%, 11 and 56 kg kg^-1, respectively, compared with farmer's N practice (REN, 18%; AEN, 3 kg kg^-1; PFPN, 20 kg kg^-1). Effective use of soil N supply and better synchronization between crop N demand and supply were main reasons for the increased N use efficiency. We conclude that the in-season N management strategy based on soil N_min test can be applied for winter wheat production in NCP for improved N use efficiency and reduced environmental contamination.