Grain Yield Construction and N Fertilizer Efficiency of Super Hybrid Rice under Different N Applications

To clarify the effects of different nitrogen application treatments on grain yield construction of super hybrid rice and utilization efficiency of nitrogen fertilizer, the nitrogen fertilizing experiment was conducted with Liangyou Peijiu, the pioneer super hybrid rice combination, as the material at Changsha, Hunan in 2001. The results showed that the applied amount of nitrogen had a significant effect on grain yield. During 0～240 kg/hm 2 (pure nitrogen), the relation of N amount to grain yield was expressed in a single peak curve with the peak (10.7 t/hm 2) of grain yield at 180 kg/hm 2 of N and with the most apparent yield increasing effect between 120 and 180 kg/hm 2 of N. The important reasons for the yield difference among different N applications were that there existed a very significant positive correlation (r=0.920 4 ** ) between N amount and spikelets per panicle and a remarkable effect of N amount on effective panicles per hectare under low N amount (0～120 kg/hm 2). Super hybrid rice had a special requirement to the source organ at heading stage and applying N had an obvious effect on the accumulation of dry matter in late stage. A higher N amount would ensure a higher LAI of super hybrid rice and maintain a higher rate of leaf dry matter and blade weight per shoot at heading stage, which is favourable to increasing the photosynthetic capability of plants and keeping from early senescence and promoting the complete transfer of photosynthates in late stage to fully make use of the great yield potentiality in super hybrid rice. There existed a great variation in the agronomic efficiency (AE) of N fertilizer among various N treatments. The highest AE (16.10) occured at the N amount of 180 kg/hm 2 and lowest (7.43) at 240 kg/hm 2.