Effect of Seedling Raising Methods on Leaf Photosynthesis and Grain Yield of Mechanically-transplanted Japonica Rice

This study was conducted to investigate the effects of seedling raising modes on photosynthetic charactedsticsand grain yield under wheat straw returning. Four representative cultivars in Huaibei area were selected as test materials. By setting potted seedlings and carpet seedlings, the effects of different nursery meth- ods on the photosynthesis of rice at different growth stages in Huaibei area were investigated. Compared with carpet seedlings, the leaf area index of potted seedlings decreased at the maturation stage, but the dry weight of leaf shewed no significant difference.The SPAD of potted seedlings had an increasing trend after transplanting, but the SPAD increased differently according to cultivars. The net photosynthetic rate, stomatal conductance and transpiration rate of the leaves of pot seeding rice were significantly higher than those of carpet seedling rice on the 85^th d after transplanting. However, theintracellular CO2 concentration and water use efficiency of leaves had no significant differences between different ＇treatments. The results indicate that the photosynthetic capacity of flag leaves of pot seedling rice is stronger in early and middle stages, but the decay rate of photosynthetic function is slightly faster than carpet seedling rice, which might be the main reason for the rice yield of potted seedlings having no remarkable difference from carpet seedlings.

Effects of soilless substrates on seedling quality and the growth of transplanted super japonica rice

This study was conducted to investigate the effects of soilless substrates of hydroponically grown long-mat seedlings （HLMS） on seedling quality and field growth characteristics of transplanted super japonica rice. A widely grown conventional super japonica rice cultivar （Wuyunjing 23） was selected as the test material. The effect of HLMS on seedling quality, mechanical transplantation quality, field growth characteristics, yield, and benefit-cost ratio were compared with seedlings grown in organic substrates and traditional nutritive soil, whJch was selected as the control. Root number, root twJstJng power and root activity of seedlings cultivated by HLMS were decreased compared to that of the organic substrates andcontrol. However, seedling root length as well as aboveground growth were increased compared to the organic substrates and control seed- lings. In the HLMS, the content of gibberellin acid （GA3） decreased while abscisic acid （ABA） content increased compared to that of the organic substrates and control seedlings. During the early stages after transplanting, the re-greening of HLMS was delayed compared to that of the organic substrates and control seedlings. Nevertheless, there were no significant differences in tiller dynamics and crop yield among the HLMS, organic substrates and control treatments. The effects of HLMS on seedling production were similar to those of the organic substrates and traditional nutritive soil in the present study, suggesting that HLMS have the potential to replace traditional nutritive soil in seedling production without decreasing crop yield. Finally, it is important to reduce organic substrates and topsoil dependence during rice seedling production and worthwhile to consider HLMS popularization and its application on a larger scale.