Effects Of Nitrogen Dressing Rate Of Panicle Fertilizer On Grain Growth And Somephysiological Characteristics Of Machine-transplanted Hybrid Rice

In2011and2012, this study was investigate the effects of different nitrogen dressing ratios on yield formation, characteristics of nitrogen accumulation, distribution and utilization, grain growth and its physiological mechanism in Machine-transplanted hybrid rice, with representative cultivar Fyou498as material and under the condition of field experiment, in Pixian Sichuan province. The main results were as follows:1Different nitrogen dressing ratios had significant effect on yield and yield components of Machine-transplanted hybrid rice. From jointing stage to booting stage, with increasing the ratio of nitrogen dressing,dry matter accumulation was decreased, but, dry matter accumulation was increased from booting stage to heading stage. With the increasing of N rate of panicle fertilizer, grain yield was increased. The results showed the treatment of ratio on base and tillering fertilizer to panicle fertilizer (7:3) was the best. In2011, as the increasing of reserving flower fertilizer, grain yield was increased. Under this same condition, grain yield was increased at first and then decreased in2012, at the same time, the treatment of ratio on promoting flower fertilizer to reserving flower fertilizer (10:0) was lowest. Again, the result proved that increasing the ratio of nitrogen dressing contributed to improving yield and its formation.2Different nitrogen dressing ratios had highly significant effect on chlorophyll content, net photosynthetic rate (Pn), and the key enzymes activities in carbon and nitrogen metabolism of flag leaf in Machine-transplanted hybrid rice. Results showed that chlorophyll content of flag leaf tended to drop off over flowering time, and chlorophyll content in N fertilization treatment was higher than that in CK treatment, and it increased as increasing the ratio of nitrogen dressing. The results showed the highest chlorophyll content was the treatment of ratio on base and tillering fertilizer to panicle fertilizer (5:5). Pn of flag leaf increased with increasing the ratio of nitrogen dressing and tended to drop off over flowering time. And, there was significant positive correlation between chlorophyll content and Pn, especially20days after anthesis, chlorophyll content had extremely remarkable correlation with Pn. Increasing the ratio of nitrogen dressing would delay senescence and promote photosynthesis of flag leaf, and increase average filling rate and maximum filling rate, related the increasing of sucrose synthase (SS), sucrose phosphate synthase (SPS), glutamine synthetase (GS), and glutamate synthetase (GOG AT) enzymes activity of flag leaf3Different nitrogen dressing ratios had highly significant effect on the final weight of a kernel (A) maximum grain filling rate (GRmax), mean grain filling rate (GRmean) and the key enzymes activities in carbon and nitrogen metabolism of grain in Machine-transplanted hybrid rice. In the grain-filling processes of superior and inferior grains, the time reaching the maximum grain-filling rate (Tpo;) of superior grains was early, but the effective grain-filling time of superior grains was short, and maximum grain-filling rate (GRmax), mean grain-filling rate (GRmean) and the final weight of a kernel (A) were significantly greater than those of inferior grains. As increasing the ratio of nitrogen dressing, the final weight of a kernel of superior grains increased, but maximum grain-filling rate (GRmax) and mean grain-filling rate (GRmean) of superior grains were increased at first and then decreased. With the increasing of N rate of panicle fertilizer, the final weight of a kernel of inferior grains was increased at first and then decreased, maximum grain-filling rate (GRmax) and mean grain-filling rate (GRmean) of inferior grains were increased. The results suggested that reasonable ratio of nitrogen dressing has significant influence on grain-filling properties, it would play an important role in improving grain-filling rate, related the increasing of sucrose synthase (SS), sucrose phosphate synthase (SPS), glutamine synthetase (GS), and glutamate synthetase (GOGAT) enzymes activity of grain.4Different nitrogen dressing ratios had significant effect on fertilizer-N accumulation, distribution and utilization of Machine-transplanted hybrid rice. The study proved that total N accumulation, apparent N recovery efficiency (ANRE) and agronomic N use efficiency (ANUE) increased with increasing the ratio of nitrogen dressing, and there was a significant positive correlation between ANRE and yield. But, physiological N use efficiency (PNUE) was reduced as increasing the ratio of nitrogen dressing, and there was a significant negative correlation between PNUE and yield, as increasing the ratio of nitrogen dressing, nitrogen uptake per100kg of grain (NAPG) was increased and then decreased. In conclusion, in order to promote grain yield, increasing the ratio of nitrogen dressing is effective way.