Effects of Nitrogen Fertilization on Growth and Grain Yield of Ratoon-rice, Tianyouhuazhan

A ratoon-rice, Tianyouhuazhan, was used to study the effects of N application rates on the photosynthetic products and grain yield of the first-season and ratoon crops. Five rates of N fertilization, i.e., N0 at 0 kg·hm^-2 (control), N1 at 69.00 kg·hm^-2, N2 at 138.00 kg·hm^-2, N3 at 207.00 kg·hm^-2, and N4 at 276.00 kg·hm^-2, were applied on the first crop. The fields were followed with a 160.50 kg·hm^-2 application rate for the ratooning. The results showed that higher N fertilizations increased the tiller number, dry matter accumulation, and transporting of storage substances to the grains, but large amount nitrogen use decreased the N agricultural use efficiency (NAUE) on the first crop. The grain yields increased by 12.12% to 23.35% over that of N0 due to the fertilizations, with the greatest production achieved by N3. The panicle count and spikelets per panicle increased with the rate increases before reaching N4 level. For the ratoon crop, the increases on grain yield ranged from 1.61% to 5.54% as compared with N0. N4 also caused a yield reduction of 4.73% over control. The panicle count of the ratoon crop decreased with rising N application, while the spikelets per panicle increased. It appeared that a N fertilization of 174.12 kg·hm^-2 for the first crop followed by 160.50 kg·hm^-2 for the ratoon crop could maximize the combined grain production.