Population quality and grain yield construction of mid-season indica hybrid rice "Wandao153" under different N applications

The effects of nitrogen application on the population quality,grain yield construction and utilization efficiency of nitrogen fertilizer in mid-season indica hybrid rice Wandao153 were investigated under field conditions.Five nitrogen treatments were set at 0 kg(N)·hm-2,150.0 kg(N)·hm-2,187.5 kg(N)·hm-2,225.0 kg(N)·hm-2,262.5 kg(N)·hm-2 and 300.0 kg(N)·hm-2 respectively.The results show that the rate of nitrogen fertilizer application has a significant effect on grain yield.Between 0 ~ 300 kg(N)·hm-2 nitrogen fertilization,indica hybrid rice yield initially increases to its maximum at 262.5 kg(N)·hm-2,and then drastically decreases at 300 kg(N)·hm-2.Relation between N application rate and grain yield follows a uni-peak curve,peaking at 11 355 kg·hm-2 grain yield of 262.5 kg(N)·hm-2,with the most apparent yield-increasing effect at 150~225 kg(N)·hm-2.The important factor for yield difference with different N application rates is variations in the number of spikelet which has a significant direct correlation with N application rate(r = 0.963 5**).Nitrogen fertilizer application markedly affects the population quality of indica hybrid rice.Appropriate N application rate enhances LAI and grain-leaf area ratio of mid-season indica hybrid rice,and also maintains higher rates of leaf dry-matter and blade weight per shoot at heading stage.This is conducive for increasing plant photosynthetic capability and dry-matter accumulation at the late stage,apparently enhancing conversion rate of dry-matter after heading,while keeping plants from early senescence and increasing lodging resistance at the late stage with high agronomic nitrogen utilization efficiency.The recommended amount of applied N for mid-season indica hybrid rice(for a super-high yield) in Jianghuai Region is 262.5 kg(N)·hm-2.