Studies on the Relationship between Ripening of Rice and the Accumulation of Carbohydrates and Nitrogen Compounds

We have been considering that nitrogen dressing at the heading stage of rice plant is rather unfavorable for the ripening. From the results of our experiments, however, it was made clear that it is possible to increase the fertility or grain weight by supplying the top-dressing of nitrogen to the rice plant which was very low in contents of nitrogen at heading stage. Furthermore higher yield was obtained by the top-dressing of nitrogen at the early period of flower primordia differentiating stage than that the heading stage. This is due to the increase of spikelets per panicle, even though the fertility and grain weight were decreased. High yielding rice plants-more than 900∼975 kg. per hectare in brown rice-showed higher fertility compared with that of the rice plants which were cultivated with the usual method. The cause of the high fertility has been considered as follows : Nitrogen content of high yielding rice plants was lower than that of ones cultivated with usual methed before heading. After heading, however, higher accumulation of nitrogen than the control was observed. Much starch was produced and stored in the straw, especially in leaf sheath and culm, in the heading stage of high yielding rice, compared with the control. After heading starch translocated rapidly into ears. Until about 20 days after heading, starch contents in the straw once decreased, but in the following period, they increased again.