[Effects of tillage mode and nitrogen application rate on nitrogen use efficiency of wheat in a farming-pasture zone of North China].

A field experiment was conducted in a farming-pasture zone in Chifeng City of Inner Mongolia Autonomous Region, North China to investigate the effects of different tillage modes and nitrogen (N) application rates on the grain yield and nitrogen use efficiency (NUE) of winter wheat. The results showed that long term conservation tillage increased the wheat NUE by 3% -4%, and decreased the environmental pollution by fertilizer N. Conservation tillage promoted the N absorption by wheat, and increased the grain yield. When the N application rate increased from 120 kg hm-2 to 360 kg . hm-2, the NUE decreased from 36. 5% to 26% , fertilizer N loss increased by about 5% , i. e. , the corresponding N loss was increased from 60 kg hm-2 to 200 kg hm-2, and the environmental N pollution increased markedly. The wheat NUE of the residual N in last season was less affected by tillage mode, but more affected by the N application rate in last season, with an overall tendency of the higher the N application rate in last season, the lower the NUE and the more the fertilizer N loss. After two seasons' wheat planting, the proportion of the total nitrogen recovery by the wheat-soil system was about 44% -50%, among which, the residual N in soil occupied about 13% -18% of applied N.