| The experiments were conducted with the conventional high-yielding nitrogen management practice (180 kg/hm2 or 150 kg/hm2N rate and basal N:tillering N: panicle N= 3:3:4), and 2 indica hybrid rice varieties with medium late maturing (Dexiang 4103, Yixiang 3724) were selected as test materials, We studied the effect of 4 panicle fertilizer application strategies (the 4th leaf-age:the 2nd leaf-age proportion= 1:3,2:2,3:1,4:0, notes for N1, N2, N3 and N4, respectively) on the population quality and grain yield under the 180 kg/hm2 N rate in 2012., We also studied 3 panicle fertilizer application strategies (the 4th leaf-age:the 2nd leaf-age proportion= 1:3,2:2,3:1, notes for N1, N2, N3, respectively) on grain yield formation and some physiological characteristics under 180 kg/hm2 and 150 kg/hm2N rates in 2013. With 2 years’ experiments, results are as follows:1. Panicle fertilizer application strategy showed significant effects on rice yield under both 180 kg/hm and 150 kg/hm N rates, although the yield between 2 varieties has a significant difference, the interaction between panicle fertilizer application strategy and cultivar was not significant. However, the interaction of panicle fertilizer application and N rate was signficant, both cultivars had higher yields in N1 under 180 kg/hm2 N rate; while achieved the highest grain yield under 150 kg/hm2 in N2 condition. As for yield components, more spikelets per panicle and total spikelets, higher seed-setting rate and 1000-grains weight were obtained, so N1 under 180 kg/hm2 N rate produced more grain; however, the higher yield in N2 under 150 kg/hm2 mainly lied on more spikelets per panicles and total spikelets.2. Panicle fertilizer application had a significant effect on differentiation and degradation of branches and spikelets, but performanced differently with 2 N rates. With the increasing of the ratio of the first panicle fertilizer under 180 kg/hm2, the differentiation numbers of primary branches, secondary branches, the spikelets on primary branches and the spikelets on secondary branches were all decreased, but the degradation numbers and the degradation rate were increased. N1 under 180 kg/hm2 had more differentiation of branches and spikelets but less degradation of branches and spikelets, so reached the highest survived spikelets number. N2 under 150 kg/hm2 had more differentiation of branches and spikelets, lower degradation rate, especially the secondary branches and spikelets on secondary branches, so the survived spikelets was also considerable.3. Panicle fertilizer application strategy had significant effects on population quality under 180kg/hm2. As the proportion of panicle fertilizer applied at 4th leaf increased, the length, width and area of upper three leaves increased rapidly, especially the sword leaf, besides, the leaf area index (LAI) and the proportion of upper three leaves in total leaves area were also increased significantly. However, the spikelet-leaf ratio was significantly reduced. The increasing of upper three leaves area increased leaf basic angle, stretch angle and droop angle, whereas the light transmittance ratio (LTR) declined, and the photosynthetic rate of 2nd leaf and 3th leaf also decreased significantly after full heading stage. With the proportion of panicle fertilizer applied at 4th leaf increased, the decreasing rate of green leaves (DRL) was accelerated, and the accumulation of assimilation products declined, but the export of stem and leaves increased significantly after heading. With the contribution of an appropriate leaf area index, the highest spikelets-leaf ratio, good LTR, higher photosynthetic rate especially 2nd and 3th leaf, lower DRL, best population quality performance, and the highest accumulation of assimilation products after heading, therefore, N1 under 180kg/hm was the optimal N management practice.4. Panicle fertilizer application strategy had significant effects on nitrogen metabolism and sugar-nitrogen ratio. The nitrogen metabolism under 180kg/hm was stronger than 150 kg/hm2 like Glutamine synthetase activity, Chlorophyll content and N content, while the sugar content and sugar-nitrogen ratio performed the opposite. These physiological performance varied under different panicle fertilizer application strategy with different N rates, the nitrogen content of N1 under 180 kg/hm2 is weaker after the first panicle nitrogen applied, then grew rapidly with the second panicle N, while the sugar content and sugar-nitrogen ratio were always the highest. The nitrogen metabolism of N2 under 150 kg/hm2 was appropriate after the first panicle N applied, and increased rapidly after the second panicle N, which was the highest at heading stage, the sugar content and sugar-nitrogen ratio were also moderate. The correlation analysis showed that sugar and sugar-nitrogen ratio was closely correlated to the differentiation and degradation of branches and spikelets. The nitrogen metabolism and sugar-nitrogen ratio of N1 under 180 kg/hm2 and N2 under 150 kg/hm2 were more harmonious than other treatments, so they had more differentiation and less degradation of spikelets. This could be the physiological mechanism influenced spikelets per panicle by the panicle fertilizer N.5. Generally speaking, panicle fertilizer application strategy should pay more attention to manage the first panicle N which affected ear differentiation mostly under 180 kg/hm2. In this N application strategy, coordinating surgar and nitrogen metabolism under a relative high level of nitrogen metabolism can increase grain number per panicle and total spikelets, optimizing leaf area and raising grain-leaf ratio can obtain a high quality of rice population. Besides, the addition of panicle fertilizer should be applied to increase chlorophyll content and slow down the decrease of greenery which would promote the photosynthetic production after flowering, the seed setting rate and 1000-grain weight would also increase. Differing from 180 kg/hm2 N rate, panicle fertilizer application strategy should focus on how to distribute the first and second panicle N, which should maintain a relative proper and steady N concentrate and sugar-nitrogen ratio, increase survived spikelets per panicle and total spikelets to gain a high grain yield. |
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