Abstract
In the early planting culture of rice at the northern parts in Japan, total number of spikelets per hill is increased, but sometimes percentage of fertile grains is lowered as compared with the standard culture. In the early planting culture, the air-dry weight of straws per hill was found heavier than that of standard culture during the initial stage of ripening and the weight decreased rapidly with the progress of ripening ; thus showing that the larger amount of reserve substances is stored in the straw and is translocated into the ears. This must be very favorable to the ripening. But when we consider the straw weight in proportion to the total spikelets, the value is always smaller during the whole process of ripening than that of standard culture. This fact may be one reason of lowered percentage of fertile grain. However, degree of decreasing of fertile grain % is smaller than degree of decrase in air-dry weight of straw per unit number of spikelets in comparison with standard culture. And, moreover, weight of 1000 hulled grains is heavier in early culture. Then, we can assume that in the early culture photosynthesis and translocation are going more actively than the standard culture during the ripening of grains, and this assumption is supported by the fact that the plants of early culture contain higher percentage of water during the period of ripening.
