Effect of nitrogen application rate on nitrogen uptake and distribution in rice

A micro-plot experiment using 15N labeled fertilizer was conducted to compare the effects of different nitrogen application rates on dry matter production, 15N uptake and distribution in two different rice cultivars, 4007 and Wuyunjing15 (WYJ15). The results obtained are listed as follows. There were no significant increments in yield of both rice cultivars if the nitrogen application rates were over N 150 kg/hm2, and the percentages of rice grain yield increase over control were 22.3%, 36.9%,43.2% and 38.1% for 4007 at N application rates of N 100, 150, 200 and 250 kg/hm2, respectively; while they were only 10.6%, 18.8%, 27.1% and 21.5% for Wuyunjing15. The 15N accumulation in grains of 4007 was much higher than in Wuyunjing15，but there were no significant differences in straws and roots between the two cultivars under the same nitrogen application rate. The 15N distribution in grains increased significantly with nitrogen application rates, but there was a reverse trend in straws, and no difference in roots of these two cultivars among N application rates. The study also showed that, at the same N application level, the total nitrogen utilization coefficient in 4007 was 3%–6% higher than in Wuyunjing15.