Analysis of Developmental Factors Determining Yield and Its Application to Yield Prediction and Culture Improvement of Lowland Rice

Abstract

1. A noticeable fact was drown out from the present experiment that the rice plants, which possess the same amount of carbohydrates and the different number of spikelets, always differ not only in the percentage of ripened grains but also in the actual number of ripened grains and in the yield of grains, and the excessive spikelets in number always act on the plant to decrease the number of ripened grains and the yield of grains on account of causing the plant to increase the number of imperfectly ripened grains which are to be eliminated in the course of threshing, husking and cleaning. From this point of view it was emphasized that the excessive growth of rice plants often brings about a rather much reduction in yield of rice-grains. 2. It was made clear that a high content of nitrogen ih rice plants at heading time, which has hitherto been considered to be more injurious than beneficial to ripening, does not damage the ripening of grains, but rather favors it, enabling rice plants to raise their photosynthetic activity. The reason why a high content of nitrogen at heading time has been considered to damage the ripening could be explained by the fact that a high content of nitrogen brings about a large number of spikelets per plant and a large number of spikelets per plant are liable to act on the plant to decrease the percentage of ripened grains. 3. The amount of carbohydrates accumulated after heading, which was proved to be most inportant in constituting the yield of rice in the present experiment, was strongly correlated with the total amount of nitrogen which is the product of the dry weight of rice plants and the nitrogen content in rice plants. And the product of the total amount of nitrogen in rice plants and the total amount of solar radiation expressed in calorie was ascertained to be highly correlated with the grain-yield. From these facts, it was pointed out that the total amount of nitrogen in rice plants at heading time would be of great importance in predicting the grain-yield of rice.