水稲収量の成立原理とその応用に関する作物学的研究 : 第73報 過繁茂の場合における稲体の受光態勢による登熟歩合診断の研究

抄録

The prime necessity to increase the grain-yield of rice is to increase the number of spikelets per unit area, whereas with an increase in number of spikelets the rice plants are very liable to grow excessively and luxuriously and the percentage of ripened grains easily goes down in general. Considering therefore that an increase of the percentage of ripened grains under luxurious growth conditions is most important for maximizing yield, the authors made an experiment to clarify the relation between the morphological characteristics and the percentage of ripened grains under luxurious growth conditions. By heavily fertilizing the rice plants which planted in the early season, and at various growth stages, moreover, by top-dressing some of them with ammonium sulphate, and on the contrary, by restricting the absorption of nutrients on some of them, the authors succeeded in obtaining various kinds of rice plants differing in morphological characteristics in receiving light. After classifying the rice plants into five groups according to the number of spikelets per unit area, the authors investigated the relation between the morphological characteristics and the percentage of ripened grains, obtaining the following results. (1) The percentage of ripened grains was negatively correlated with each length of the flag-leaf (uppermost)-blade, second (penultimate) leaf-blade and third leaf-blade, and with the sum of length of the flag-leaf-blade and second leaf-blade and also that of the flag-leaf-blade, second leaf-blade and third leaf-blade. Among these characters the sum of length of the flag-leaf-blade and the second leaf-blade showed the highest correlation to the percentage of ripened grains. (cf. Fig. 5). (2) The percentage of ripened grains was also negatively correlated with each curvedness of the leaf-blabe of the flag-leaf, second-leaf and third leaf, and with the sum of curvedness of the flag-leaf and second leaf, and that of the flag-leaf, second-leaf, and third leaf. Among these characters the sum of curvedness of the leaf-blade of the flag-leaf and the second-leaf showed the highest correlation to the percentage of ripened grains. (cf. Fig. 8) By the curvedness of the leaf-blade is meant the quotient which is given by dividing the actual length (the arc) of a leaf-blade by the distance (the chord) between its auricle and the top of its curved leaf-blade. (3) The percentage of ripened grains was also negatively correlated with each angle of the stem to the flag-leaf as well as the second leaf, and also with the sum of these two angles. In partiqular, the sum of these two angles showed the strongest correlation to the percentage of ripened grains. (cf. Fig. 13) (4) In any cases above mentioned the second leaf-blade showed the closest relation to the percentage of ripened grains. It was pointed out, therefore, that for forecasting or diagnosing the percentage of ripened grains stress should be laid on the morphological characteristics of the second (penultimate) leaf-blade.