[Effect of nitrogen management modes on grain yield, nitrogen use efficiency and light use efficiency of wheat]

A nitrogen management experiment with three nitrogen levels (0, 120, and 180 kg·hm^-2, namely N₀, N₁₂₀, N₁₈₀) and three nitrogen allocation modes (N_A: base fertilizer 100%; N_B: base fertilizer 70% + seedling fertilizer 30%; N_C: base fertilizer 60% + jointing fertilizer 40%) was conducted at four sites (Chongqing, Renshou, Guanghan and Xichang) during two consecutive years, the SPAD value, canopy photosynthetic rate (CAP), photosynthetically active radia-tion (PAR) interception efficiency and grain yield were determined, and the nitrogen use efficiency and PAR use efficiency were calculated. The results showed that the SPAD of upper-most three leaves, CAP, PAR interception efficiency and grain yield were promoted with increasing nitrogen fertilizer, but nitrogen fertilizer use efficiency, productivity efficiency, uptake efficiency and use efficiency were decreased. The promoting effects of nitrogen fertilizer postponing were different among nitrogen levels, with the highest SPAD in N₁₈₀ treatment and the highest CAP in N₁₂₀ treatment. The light use efficiency of different nitrogen fertilization patterns differed among four sites. Furthermore, nitrogenous fertilizer postponing significantly increased nitrogen agricultural fertilizer use efficiency, productivity efficiency, uptake efficiency and apparent nitrogen recovery efficiency, but declined nitrogen use efficiency, and the performance of N_C was better than N_B. Among different sites, Guanghan had the highest SPAD, CAP, PAR interception efficiency and grain yield, Xichang had higher SPAD and nitrogen use efficiency, lower CAP and PAR use efficiency, Chongqing and Renshou had the lowest SPAD, light use efficiency, nitrogen use efficiency and grain yield. Biomass had significant positive relationships with grain yield, CPA, SPAD, and PAR interception efficiency. Therefore, the increase of nitrogen fertilizer could promote yield at all sites, and nitrogenous fertilizer postponing could further optimize grain yield component and improve nitrogen and light use effi-ciency. But the effects depended on the years and sites, thus a target nitrogen management mode should be site-specifically made.