Abstract: A field experiment was carried out to study the synergistic effects of transplanting density and nitrogen application rate on yield formation and nitrogen use efficiency of rice (cultivar Nanjing 9108). We set up three basic seedling densities of D₁ (90×10⁴ ind·hm^-2), D₂ (120×10⁴ ind·hm^-2), and D₃ (150×10⁴ ind·hm^-2), and four nitrogen application rates of N₁ (0 kg·hm^-2), N₂ (240 kg·hm^-2), N₃ (270 kg·hm^-2), and N₄ (300 kg·hm^-2). The results showed that under treatment N₂D₃, spikelets per panicle and filled grain percentage of rice were relatively small, but the effective panicle number was 29.3% higher than that of N₂D₁ and N₂D₂, which indicated that the higher number of effective panicles of rice resulted in unchanged yield. The biomass yield of N₂D₃ was 17.0% higher than that of N₂D₁ and N₂D₂, and such obvious enhancement of biomass yield ensure the high yield of rice. N₂D₃ treatment significantly increased rice nitrogen accumulation by 13.8% and nitrogen dry matter production efficiency by 7.1%. There was no variation in nitrogen use efficiency of grain yield of rice, but the nitrogen harvest index significantly decreased under the treatment of N₂D₃. Compared with N₂D₁ and N₂D₂, N₂D₃ treatment increased the N fertilizer absorption and utilization rate, partial productivity, agronomic utilization rate, and physiological utilization rate by 32.4%, 13.8%, 54.6% and 17.1%, respectively. Higher nitrogen application rate ensured the higher available nitrogen content in soil under different transplanting densities. When the input of nitrogen fertilizer was low, soil available nitrogen content could maintain a high level under high transplanting density. In conclusion, on the basis of conventional nitrogen application rate of 300 kg·hm^-2, by increasing planting density of rice and 20% reduction of nitrogen fertilization rate, the D₃N₂ treatment could ensure rice yield, improve N absorption and N use efficiency of rice, and maintain soil fertility of paddy field.

Key words: rice, yield, transplanting density, nitrogen input, nitrogen uptake and use efficiency.