Climatic responses of biomass production and grain yield in Japanese high-yielding rice cultivars under different transplanting times

Planting time is one of the management methods determining yield potential in rice. The aims of the present study were to determine whether early transplanting improves yield potential in temperate regions of Japan, and to identify quantitative influences of climatic factors on crop productivity. We evaluated differences in biomass production and yield formation under three transplanting times for high-yielding cultivars having different heading characteristics. Early transplanting extended growth duration, but did not increase biomass production before heading, resulting in no improvement in total spikelet number and yield potential. For all the cultivars, cumulative air temperature better explained differences in biomass production under different transplanting times than did cumulative solar radiation. The results indicate that early-transplanted plants could not effectively utilize solar radiation for CO2 assimilation and that early biomass production in early-transplanted plants was constrained by low temperature. On the other hand, biomass production after heading and grain filling in late-heading cultivars were reduced with late transplanting time, owing to lower solar radiation and lower temperature. These results suggest that avoiding late transplanting can increase final biomass as well as acquire stable and high grain yield in late-heading cultivars in temperate regions, even if early biomass production after transplanting is reduced by low temperature. Two indica-dominant cultivars showed the highest grain yield and biomass productivity in the present study, but showed higher base temperature for biomass production, indicating that inidica-dominant cultivars were susceptible to low temperature. Development of a management method and genetic modification to promote early biomass productivity at low temperatures is necessary for further improvement of yield potential of high-yielding cultivars in temperate regions.