Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : CIV. Effects of light intensity and different shading methods during the ripening period on the percentage of ripened grains

摘要

Matsushima. one of the authors, reported in the previous paper (1957) that the more intense light intensities than 0.6 cal./cm2/min. or 350 cal./cm2/day were almost of no use for increasing the percentage of ripened grains and he made the he made the fact as an evidence of his experimental results that the light-curves of carbon assimilation even in rice plant communities show a saturation point at about 0.6 cal./cm2/min. However, after the authors ascertained that the light-curves of carbon assimilation did not always show a saturation point in rice plant communities, as shown in the previous papers (No. 102 and 103), they considered that the above-mentioned fact would be a different one under luxuriant growth conditions and under different shading treatments. Therefore, they re-examined the relation between the percentage of ripened grains and light intensity by using two different communities, i. e. one is 4.3 and the other is 7.0 in the leaf-area-index, and two different shading methods, i. e. one is the shading with white clothes and the other with lattice plates made of vinyl chloride. (The former shading method increases the pepcentage of the amount of diffused light to the total amount of sunlight, while the latter neither increases nor decreases the percentage.) The results obtained can be summerized as follows. 1) The relation between the light intensity during the ripening period and the peroentage of ripened grains (or the weight of non-winnowed 1, 000 grains) appears to show the curves with a light saturation point in a plant community having a low leaf-area-index as reported before, while it indicates the curves with no saturation point in a plant community having a high leaf-area-index. 2) Even if the light intensity is equal to each other shading method, the percentag of ripened grains (or the weight of non-winnowed 1, 000 grains) is always higher in the cloth shading method than in the lattice shading. On the basis of this fact it has been pointed out that in the shading experiments the percentage the percentage of the amount of diffused light to the total amount of sunlight should be taken into consideraton. 3) The reason why in the past experiments the more intense light intensities than 0.6 acl./cm2/min. or 350 cal./cm2/day are of no use for increasing the percentage of ripened grains may be explained as follows. In the shading experimnets conducted in the past rice plant communities used are all low in the leaf-area-index and consequently the number of grains per unit area is very small, and moreover the shading methods used are all conducted by using white cloths and percentage of the amountof diffused light is much larger in the treatments than in the natural conditions. 4) As a result of investigation on the distribution in specific gravity of imperfectly ripened grains (lighter than 1.06 specific gravity), the following facts heen clarified : The perceotage of ripened grains is much influenced by the number of imperfectly ripened grains which are lighter than 0.86 specific gravity and the caryopsis developments of which have stopped at the early ripening stage, and the occurrece of them can be ascribed to the shortage of the amount of carbon assimilation at the time at which the starch-content in culms attains its minimum.