Effect Of Seedling Age On Premature Heading And Yield In Rice

Due to the fast increase in population and requirement for land in economic development, area of arable land and food security is facing tremendous challenges in China. It is important to achive high grain production with the available land. Rice(Oryza sativa L.) is one of the most important food crops in China. One potential way to increase rice production with current land is to increase rice harvest frequency. Double- and triple-season rice contributed significantly to the increase in rice production in China, however, there are many obstacles for the adoption of multiple cropping in rice production with seedling age as one major one. It was found that prolonged seedling age could significantly reduce rice grain yield and cause premature heading(PH). However, it is still obscure about the relationship between premature heading and yield penalty under long nursery duration, and strategies to overcome these negative effects from prolonged seedling age. Thereore, the objectives of this study wereto(1) investigate the response of grain yield and yield components, plant morphology and growth to prolonged seedling age,(2) understand the mechanism of yield decline caused by PH, and(3) to explore whether different crop management practices could alleviate the negative effects. Field experiments were conducted at the experimental station of Zhougan and Zhangbang Villages, Dajin Town, Wuxue Country, Hubei Province, China, in both early season and late season from 2013 to 2014, and there were three crop management modes: farmer’s practice(FP), super-high yield(SH), and high yield and high efficiency(HH) and two seedling age treatment: CK(about 30 days of seedling age) and long seedling treatment(LS,about 40 days). The main results are:1. Grain yield was significantly reduced under LS treatment. Except for the late season rice in 2013, grain yield of LS treatment reduced significantly by 11.73%compared with CK. The yield reduction was mainly due to decrease in biomass production, spikelets number and grain weight.2. Premature heading was observed in LS treatment. In comparison with CK treatment, main stems under LS treatment head aound 8-13 days earlier, but tillers 8 days later. Grain yield, biomass, spikelets per panicle and grain weight of PHS stems decreased by 39.95, 38.30, 37.48 and 8.38%, respectively.3. Compared with CK, the surviving secondary branch number of PHS reduced by 8.11%, and the number of degenerated secondary branch and spikelets per panicle increased by 41.72% and 65.63%, respectively in 2013. In 2014, the numberof surviving primary and secondary branch of PHS decreased by 22.10% and 25.87%, respectively, and the degenerated spikelets number per panicle increased by 87.64%. No significant difference between NS and CK in spikelets and branches degeneration. Moreover, SPAD value in the flag leaves of PHS was significantly lower than CK, which indicated fast senescence in flag leaf of PHS.4. The vegetative growth of PHS stem was restricted. Significant declines in panicle height, stem height and leaf area per stem were observed by 24.46%, 34.31% and 36.33%, respectively in 2013.Plant height, panicle height, stem height and leaf area per stem decreased significantly by 17.24%, 29.90%, 40.21% and 61.97%, respectively in 2014. Difference between CK and NS was relatively small.5. Crop management practices and soil fertility have an impact on the growth of stems bearing the premature-heading panicles, however, they could not alleviate the negative effects caused by prolonged seedling age. Compared with Zhougan, PH had a more significant effect on the plant height, panicle height, stem height, leaf area index(LAI), numberof surviving secondary branch and spikelets per panicle in Zhangbang. Low soil fertility may increase the influence of PH on plant growth. In general, No significant differences were obeseved in the reduction of grain yield and growth of PH among the three crop management practices.In a word, the study demonstrated that prolonged seedling age could induce the occurrence of premature heading. The reduced vegetative growth of PH stems leads to lower sigle-stem grain yield compared with CK. Together wth the alteration in the pattern of heading, PH resulted in reduction of grain yield. Our study indicated that crop management practices and soil fertility could not alleviate the negative effects caused by prolonged seedling age. More study should focus on the difference in response to prolonged seedling age of different early- and late-season varieties. In rice production, more attention should be given to avoid long nursery duration.