[Effects of postponed basal nitrogen application with reduced nitrogen rate on grain yield and nitrogen use efficiency of south winter wheat].

Excessive nitrogen (N) fertilizer application has led to a reduction of nitrogen use efficiency and environmental problems. It was of great significance for high-yield and high-efficiency cultivation to reduce N fertilizer application with modified application strategies. A two-year field experiment was conducted to study effects of different N application rates at basal and seedling application stages on grain yield and nitrogen use efficiency. Taking the conventional nitrogen application practice (240 kg N·hm with application at basal, jointing, and booting stages at ratios of 5:3:2, respectively) as control, a field trial was conducted at different N application rates (240, 180 and 150 kg N·hm, N, N and N, respectively) and different application times [basal (L), fourth (L) and sixth leaf stage (L)] to investigate the effects on grain yield and nitrogen use efficiency. The results indicated that grain yield decreased along with reducing the N application rate, but it had no significant difference between N and N while decreased significantly under N. Nitrogen agronomy and recovery efficiency were all highest under N. Among different N application stages, grain yield and nitrogen use efficiency were highest under L. NL had no signifi-cant difference with control in grain yield, but its nitrogen use efficiency was significantly higher. The leaf area index, flag leaf photosynthesis rate, leaf nitrogen content, activity of nitrogen reductase and glutamine synthase in flag leaf, dry matter and N accumulation after jointing of NL had no significant difference with control. In an overall view, postponing basal N fertilizer application at reduced nitrogen rate could maintain high yield and improve nitrogen use efficiency through improving photosynthetic production capacity and promoting nitrogen uptake and assimilation.