水稲収量予察の作物学的研究 (予報) : 〔V〕 収量構成4要素の決定時期特に決定終期に就いて

抄録

The authors made an experiment to know of the periods in which the values of 4 factors constituting the yield of rice are determined and especially the end of the periods. The experiment had two treatments; the one was a pruning treatment of all blades and the othar was that of all roots. Both treatments were carried out in the field, according to 4 randomized blocks method, on different dates ranging from 15th day after transplanting to maturity with an interval of 2∼5 days. The material was the medium maturing variety, Norin-No. 25, and 12 plants were used in eacn treatment. Examining the degrees of influences caused by treatments with the help of modern statistics, the authors could accomplish their purpose to a considerable extent. (1) Number of ears per plant seemed to be mainly determined by the time of the beginning of young panicle formation, and not to be influenced by external conditions in the periods after the stage of the beginning of generative cell formation. (2) The influence upon the number of spikelets per ear began to appear at the stage of the first bract primordia differentiation (approximately 32 days before heading), and it became severest at the beginning of reduction division (13 days before heading), and it finished by the time 5 days before heading. (3) Fruiting percentage began fo be affected from the stage of first bract primordia differentiation, and became most susceptible at the time 7 days defore heading in the blade treatment and at the time immediately after and 23 days after heading in the root treatment, and it held constant in and after the period 33∼38 days after heading. The reasons why the most susceptible periods occurred as mentioned above were explained by transpiration of leaves and regenerating ability of blades and roots after treatment. By the way, only, grains heavier than 1.06 in specific gravity were recognized as fruited grains. (4) Weight of 1, 000 grains began to be affected from the stage of the beginning of young panicle formation (27 days before heading); and became most susceptible at the stage of beginning of generative cell formation (18 days before heading) and in the period between immediatly after and 28 days after heading, and this susceptible period ended at the time 38 days after heading. The fact that one of the most susceptible periods exists before heading seemed to offer some promise in forecasting the weight of 1, 000 grains. (5) Yield of grain was affected by the time at which the first treatment carried out, and became constant in and after the period 33-38 days after heading. The periods, in which the poorest productions were brought about, were found at the stage of the most vigorous tillering, the beginning of reduction division, and immediately after and 23 days after heading in the root treatment; but the period was found only at the stage when almost all upper-most leaf-blade appeared out of the subordinate sheathes (7 day before heading) in the blade treatment. As a result of comparing the ability of 4 factors of controlling the yields, representing them in logarithmic values, it was made clear that number of ears in the period before the beginning of young panicle formation, number of spikelets per ear and fruiting percentage in the period between the beginning of young panicle formation and the time 5 days before heading, and fruiting percent in the period after that had the greatest influence on the yields respectively. As a whole, weight of 1, 000 grains seemed to have the least influence upon the yields, but fruiting percentage the largest. (6) Basing on the fact that the better yields and the higher fruiting percentages were obtained in the cases of the earlier and the later blade-treatments than that of the stage, 7 days before heading, empirical formulas were also derived, which will be utilized in estimating yields in crop-failures caused by various disasters.