Study on Population Characteristics and Formation Mechanisms for High Yield of Pot-Seedling Mechanical Transplanting Rice

【Objective】The characteristics of yield formation and population dynamics and mechanisms of high-yielding formation were identified in pot seedling of mechanical transplanting japonica rice.【Method】Twenty-four japonica rice cultivars which have different weights of single panicle were grown by unified high-yielding cultivation in 2010, and were divided into three panicle types by clustering analysis with average single panicle in maturity. Three panicle types of japonica rice cultivars including large panicle type(LPT, Yongyou 2640 and Yongyou 8) and medium panicle type(MPT, Wuyunjing 24 and Ningjing 3) and small panicle type(SPT, Huaidao 5 and Huaidao 10) were field-grown from 2011 to 2012 in Diaoyu town, Xinghua County, Jiangsu province, China. By setting carpet seedling of mechanical transplanting rice(CS) as CK, the yield and yield formation, number of population stem and tiller, leaf area index(LAI) and dry matter accumulation of pot seedling of mechanical transplanting rice(PS) were investigated, and high-yielding formation mechanisms of PS were also explored in respect of seedling quality, matter accumulation after transplanting, plant type, staged photosynthetic matter production, photosynthetic potential(PP), crop growing rate(CGR) and net assimilation rate(NAR), matter transport in stem and sheath and root activity. 【Result】 Yield was significantly or very significantly higher in PS than CS. The range of increased yield was 8.71%-11.11% in large panicle-type variety, medium panicle-type variety was 6.85%-7.89%, and small panicle-type variety was 5.30%-6.34%. The increased yield was mainly attributed to higher total spikelets in PS, which owning to sufficient panicle and expanding spikelets per panicle. Compared with CS, PS had earlier tiller, suitable peak seedling tillers, slower reducing rate of tillers after jointing, enough effective panicles and higher ratio of productive tillers to total tillers at maturity. Leaf area index and dry matter accumulation in PS was significantly higher at the critical stage for effective tiller and very significantly greater at and after booting stage, and higher 5.17%-11.00% and 5.36%-9.20% at maturity than CS. The mechanisms of high-yielding formation in PS was that: After transplanting, there had strong seedling, better population started quality, earlier seedling establishment, faster tiller, more tillers of low position and greater dry matter weight of aboveground and root; They formed higher photosynthetic efficiency and quality population at heading, which had tighter plant type, better canopy, bigger leaf area, higher specific leaf weight, stronger stem and sheath, greater grain-leaf ratio; At the late growing stage, there had stronger root activity, slower decreasing rate of leaf area, higher photosynthetic potential and crop growing rate and net assimilation rate, greater dry matter accumulation, more coordinated matter export and translocation of stem and sheath. 【Conclusion】With better population started quality and earlier tiller, pot seedling of mechanical transplanting rice had obvious advantages, especially, higher photosynthetic matter production and greater dry matter accumulation at the middle and late growing stages, which the yield formation characteristics were sufficient panicle, larger panicle type and more spikelets per panicle.