Abstract
This experiment was carried out to know what sort of factors at the time of heading show close relation to the increase of top-dry-weight, and serve as successful index to forecast the yield. The two paddy rice varieties, Asahiyori and Yutakasenbon having different vegetation form with each other, were grown in the paddy field under different conditions of nitrogen supply, and light intensities. The results obtained were as follows: 1) The amount of total nitrogen contained in leaf-blades as well as the dry weight of leaf-blades per unit area at the beginning of ripening stage were closely related to both increment of top-dry-weight per unit field area in ripening period and the ultimate yield. Therefore, it seems possible to forecast the yield by the weight of leaf-blades at the beginning of ripening stage. 2) When the weight of all grains was to be forecast, the figures showing the dry weight of leaf-blades were useful enough, irrespective of varities, but, when the brown rice yield must be forecast, the figures were insufiicient, because there was a slight difference in the trash rice amount between varieties. 3) The figures of leaf-blades weight per grain (leaf-blades dry weight/number of total grains) at the beginning of ripening stage was of much importance. It related closely to the percentage of ripening graines, the trash rice weight, the percentage of trash rice weight and also to the weight of 1000 grains. Therefore, forecasting of these seems to be possible by the figures of the dry weight of leaf-blades. 4) The leaf area index at beginning of ripenning stage was within frorn 2.5 to 3.9 scope in this experiment.
