Effect of seedling age on yield and population quality of mechanized transplanted hybrid rice

As a modern and high efficient rice production mode, rice mechanized transplanting has been a principle development trend in China. Subject to geographical conditions, the development of rice mechanized transplanting in Sichuan, the largest rice production region in southwest China, is very slow, only account for 6.2% of total rice planting area in 2012, while the average ratio was 26% across the country. So the development of rice mechanized transplanting in Sichuan is urgent and meaningful. The optimal seedling age and variety is an essential problem should be solved. In this experiment, the effects of different seedling ages on yield and population quality of middle and late maturing hybrid rice in mechanized transplanting were studied. The experiment was conducted in Wenjiang, a representative plain region in Sichuan, from April to October during 2011 growing season. The experiment was designed as split plot with seedling age as main plot and variety as sub-plot with three replicates. Three different seedling ages as the main plot were 21, 28 and 35 days, and four rice varieties were selected with growth duration of middle and late maturating, respectively. Chuanxiang 3 and Fuyou 838 (142 days and 145 days growth duration) are middle maturing rice, while F-You 498 and Gangyou 725 (148 days and 150 days growth duration) are late maturing rice. The climate conditions during seedling stage in 2011 were representative and consistent with that of recent 5 years in precipitation, sunshine and temperature. The seedling rate of each seedling tray was 80 gram and seedlings were transplanted at a hill spacing of 30 cm × 15 cm, each plot covered 19.2 m2. The nitrogen fertilizer amount was 150 kg/hm2, and the amount of potash and phosphate are 90 kg/hm2 and 75 kg/hm2, respectively. The other managent measures were at a uniform with high-yield cultivation. The experiment results showed that all indexes were better than that of larger seedlings rice in mechanized transplanting, including grain yield, tillers at the effective tillering of critical leaf age (N-n), percentage of productive tiller, leaf area index, photosynthetic rate of flag leaf after heading, light transmission of groups, leaf area rate of productive tillers at heading and its ratio, leaf area from flag leaf to 3rd leaf from top of productive tillers at heading and its ratio. As for varieties, on both grain yield and various rice population indexes, the late maturing varieties were better than the middle maturing ones significantly, especially for F-You 498. F-You 498 showed medium tillering ability and ideal plant type, which is beneficial for improving light interception and reducing unproductive tillers, contributing to an excellent population photosynthetic production and a larger grain number per spike. Besides its impressed yield ability, F-You 498 got a better seedling flexibility, it can remained a relative high grain yield when seedling age extended to appropriately 28 days. In the middle maturity group, although Fuyou 838 have more number of panicles, their spikelets per panicle are poor, which restrict the yield increase. In this progress, too many unproductive tillers caused by immoderate tillers should be the main reason.