Differences of nitrogen uptake, utilization and translocation between indica and japonica super rice

【Objectives】Currently, a large amount of super rice varieties are bred in China to excavate the high yield potential in rice production. Nitrogen is one of the most active factors for rice growth, yield formation and grain quality. The characteristics in N uptake, utilization and translocation of both indica and japonica cultivars and their relationship with yield formation, and the yield formation mechanisms of japonica super rice related with N nutrition are fully discussed in this paper. 【Methods】Five representative super hybrid indica rice and five conventional japonica super rice cultivars are used as materials in Suzhong region with ricewheat cropping rotation in 2011-2012 N content and N accumulation at the main growth stages, periodic N uptake rate and accumulation, N using efficiency, and N translocation amount, apparent N translocation rate and N translocation conversion rate in stemsheath and leaf from heading to maturity are analyzed systematically. 【Results】 1) The average grain yield, total N accumulation and N uptake per 100 kg of grain of japonica rice are 10.89 t/ha, 224.50 kg/ha and 2.79 kg, which are 13.21%, 32.74% and 17.45% significantly higher than those of indica rice. 2) N accumulation of japonica rice is higher than that of indica rice significantly from transplantingcritical leaf-age for productive tillers stage, jointing-heading stage and heading-maturity stage, while it shows an opposite tendency from critical leaf-age for productive tillers-jointing stage. The periodic N uptake rate follows the same trend as N accumulation. 3) The N contents in leaves, stems, sheaths, panicles at both the heading and maturity stages and the entire rice plants throughout the growth stage of japonica rice are higher than those of indica rice significantly. 4) The N recovery efficiency and agronomic efficiency of japonica rice are slightly higher than those of indica rice, while the N physiological efficiency, N using efficiencies for grain and biomass production, the partial factor productivity of applied N are opposite accordingly, reaching an significant level, except for the N physiological efficiency. 5) At the maturity stage, the ratios of N accumulation in stemsheath and leaves are significantly higher than those of indica rice, but lower N accumulation in panicles of japonica rice leading to the significantly lower N harvest index in japonica rice than in indica rice. 6) The N translocation amount, apparent N translocation rate and N translocation conversion rate in stemsheath and leaves from the heading to the maturity of japonica rice are all significantly lower than those of indica rice, but no significant difference for N translocation conversion rate of sheaths. 7) For the indica rice, the principal grain N is transferred from the N stored in the source organs at the heading stage, while for the japonica rice, the grain N is heavily dependent on the N rapid absorption from the jointing to the maturity stage. 【Conclusions】The proper N management for japonica rice is to control N uptake at transplantingjointing stage, promote periodic N uptake and accumulation at the jointingmaturity stage to satisfy the need of rapid N accumulation and high grain yield.