Crop scientifical studies on the yield-forecast of lowland rice. : Preliminary report : II. Relations between the yield of lowland rice crop and its constituting factors and interrelations among them.

By using the data of experiments for nineteen years on climate-adaptability of rice crop at Konosu Agricultural Experiment Farm, correlation coefficients between the yield of rice crops and its constituting factors and among those individual factors were calculated. And the results were summarized as follows. (1) Correlations between the yield and the number of panicles were possitive in all varieties, and differences of the coefficients among early, intermediate and late maturing varieties were insignificant. (2) Correlation coefficients between the yield and the number of spikelets per panicle were high in early varieties and low in late ones. (3) Fruiting percentages were most strongly correlated with the yields in late varieties and most weakly in intermediate ones. (4) Correlation coefficients between the yield and the weight of 1, 000 grains were low in early varieties and high in late ones. The later the maturity of a variety was, the higher its coefficient became. (5) In short correlation coefficients between the yield an its constituting factors, except the number of panicles, were very different in earliness of varieties. The factors strongly correlated with the yield were considered to act as the limiting factors of the yield determination component in consequence of their insufficient development caused by unfavourable environmental conditions in the growing stage in which their values are destined. (6) Correlation coefficients between the number of panicles and, spikelets were possitive in early varieties but significantly negative in late ones. This seemed to be closely connected with the fact that a meteorological good condition in the second and third decades of July increased the number of panicles of all varieties and of spikelets of early varieties but obviously reduces the number of spikelets of late varieties, and the later it matures the more decreases the number of spikelets. (7) Number of panicles was negatively correlated in general with the fruiting percentage and the weight of 1, 000 grains in early and intermediate varieties. (8) Correlation coefficients between the number of spikelets and the fruiting percentage or the weight of 1, 000 grains seemed to scarcely relate to the important characters of varieties. (9) The fruiting percentage of late varieties were strongly correlated with the weights of 1, 000 grains. This seemed to be based on the fact that these two factors of late varieties are greatly influenced by the air temperature in September and October. (10) From the relation between number of panicles and other three factors it was suggested that the values of the three factors can be predicted, however may it be much or little, at the growing stage during which the number of panicles can be forecasted. And also the yield-forecasting method on late maturing varieties which is seriously desired at the present time may become practicable to a certain extent at the stage when the fruiting percentage can be foreseen by utilizing the correlation between the fruiting percentage and the weight of 1, 000 grains in late varieties.