Effects of different transplanting densities on population development and grain yield of double cropping super rice.

Using two super hybrid rice combinations Luliangyou 996(early rice) and Ganxin 688(late rice) as the materials,the effects of different transplanting densities(D1~D4 for early rice and M1~M4 for late rice) on the population development and grain yield of double cropping super rice were studied.The results showed that the grain yield,dry matter yield,and nitrogen accumulation of Luliangyou 996 grown as early rice increased with the density,but the grain yield and N accumulation of Ganxin 688 grown as late rice were higher in the treatments of M2 and M3 with medium densities.The effective tillering stage was postponed with reduced transplanting density.The number of maximal tillers and effective panicles increased with the density.The number of effective panicles and the number of basic transplanting seedlings were positively correlated.The percentage of effective tillers was negatively correlated with the number of basic transplanting seedlings and the number of maximal tillers.Lower density was favorable for increase of effective tiller percentage.The number of transplanting basic seedlings had a greater effect on effective panicles in early rice than in late rice.Late rice had a better self-regulation of the population than early rice.The number of spikelets per panicle and seed setting percentage decreased with the increase of transplanting density.The retrogression percentage of secondary panicle branches and spikelets was closely related to its differentiation number.