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The information available on the environmental and plant characteristics that contribute to rice yield variation over a wide range of regions would be useful for understanding the generalized determinants of rice yield. In this study, we extracted the data (n = 107) of grain yield, biomass production, harvest index, intercepted radiation, radiation use efficiency (RUE), incident radiation and intercepted percent from 5 published studies conducted in 6 locations across 3 countries and evaluated the relationships between the parameters. A very large variation in grain yield, from 3.31 to 16.50 t ha −1 , was observed. About 73% and 6% of the yield variation was explained by biomass production and harvest index, respectively. Biomass production was strongly positively related to intercepted radiation. However, intercepted radiation would be difficult to further increase because it was related much more closely to incident radiation than to intercepted percent. Although RUE did not explain the variation in biomass production, it varied by nearly two fold (0.99-1.88 g MJ −1 ). Our study highlights the need for a comprehensive understanding of the various aspects of RUE in rice.

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This study was conducted to identify the factors associated with high grain yield in single seedling machine-transplanted hybrid rice under dense planting conditions. Field experiments were done in Yong'an Town, Hunan Province, China in 2015 and 2016. Two hybrid rice cultivars were grown under single seedling machine transplanting (SMT) and conventional machine transplanting (CMT) at a high planting density in each year. Grain yield and yield attributes were compared between SMT and CMT. Averaged across cultivars and years, grain yield was 12% higher under SMT than under CMT. Plant height, basal stem width, and shoot and root dry weights were higher in seedlings for SMT than for CMT. SMT had less maximum tiller number per m 2 and consequently less panicle number per m 2 than did CMT. Branch number per panicle, especially the secondary branch number per panicle, and spikelet number per cm of panicle length were more under SMT than under CMT, which resulted in more spikelet number per panicle under SMT than under CMT. SMT had higher or equal spikelet filling percentage than did CMT. The difference in grain weight between SMT and CMT was relatively small and inconsistent cross years. SMT had higher or equal total biomass and harvest index than did CMT. Dry weight per stem under SMT was heavier than that under CMT. Larger leaf area per stem was partly responsible for the heavier dry weight per stem under SMT than under CMT. Our study suggests that improvement in seedling quality, panicle size, and dry weight per stem are critical to the high grain yield in single seedling machine-transplanted hybrid rice under dense planting conditions.