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^-2and 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^-2grain 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.