Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice. : LXXXII. Effect of nitrogen depletion at different growth stages on the growth and yield of rice.

摘要

Growing rice plants in solution culture under a community condition and stopping nitrogen supply for 20 days at different stages of growth, the authors studied the effects of nitrogen depletion at various growth stages on the growth and yield of rice. As previously reported, no supply of nitrogen during the critical growth period in which the plant type after heading was predetermined made the rice plant decrease the number of spikelets per unit area, length of lower three internodes and upper three leaf-blades, but increase the amount of carbohydrates in straw at heading stage, and as a result of it, favoured ripening and prevented the plant from lodging. The three treatments which stopped nitrogen supply for 20 days from 59, 49 and 42 days before heading respectively were high in grain yield on account of the percentage of ripened grains being much increased. This high percentage of ripened grains in the present experiment could firstly be ascribed to decreasing the number of spikelets per unit area and increasing the amount of carbohydrates in straw at heading stage, and secondarily to controlling excessive growth, improving plant type and preventing the plant from lodging. The length of upper three leaf-blades was shortest in the treatment which stopped nitrogen supply during the period from 42 days to 20 days before heading, and the length of lower three internodes of rice plants was shortest in the treatment which stopped nitrogen supply from 49 days to 31 days before heading. In this experiment, however, the effect of improvement in plant type and light-utilizing efficiency on the rate of carbon assimilation, the increase in dry-matter after heading and the grain yield were hardly recognized, probably because the leaf-area-indexes in the experiment were not so high enough as the plant type could affect the photosynthetic efficiency. So far as the experiment was concerned, the amount of photosynthetic production after heading was mainly governed by the amount of nitrogen in leaf-blades at heading time as well as that of nitrogen supply after heading, and scarcely affected by the leaf-area-indexes, leaf-length and light-utilizing efficiency. (The plant type would play an important role in increasing photosynthetic production after heading when the leaf-area-index would be higher than 6.4.) The results in the present experiment are considerably different from those of pot experiments in same kind so far conducted, probably because the light condition after heading is so good in pot experiment that the grain yield is simply increased by only increasing the number of spikelets per unit area.