Factors Affecting Variance in Yield Caused by Different Transplanting Times in High-Yield and Good-Eating-Quality Rice

Abstract

To avoid farm work competition and explore the possibility of diversification of cropping, we evaluated the yield and yield characteristics of the transplanting times (early, middle and late) in rice (Oryza sativa L.) for three years using three high-yielding cultivars, “Akidawara”, “Yamadawara” and “Toyomeki”, which have high eating quality. The later the transplanting time, the lower the filled brown rice yield. Sink capacity and the increase in shoot dry weight during grain filling tended to be smaller the later the transplanting time. To reveal the factors lowering the yield in late transplanting, we carried out several analyses under various climate conditions. The relationship between Y/S value, obtained from dividing yield (Y, g m^–2) by cumulative solar radiation (S, MJ m^–2) from 30 days before heading to 20 days after heading, and the average daily temperature in the same periods were approximated by a quadratic equation, meaning yield could be explained well by temperature and solar radiation. The maximum value in Y/S was found at around 23.4 to 24.0 ºC. On the other hand, it was inferred that the lower yield in late transplanting was affected not by the average daily temperature before and after heading but by the lower average daily solar radiation.