Analysis of Developmental Factors Determining Yield and Its Application to Yield Prediction and Culture Improvement in Lowland Rice. : LI. Effects of top-dressing with ammonium sulfate on the grain-yield and its constitutional factors at critical periods relating to determination of each yield-constitutional factor.

Abstract

Examining the effects of top-dressing with ammonium sulfate under different amounts of basic fertilizer on the grain-yield and its constitutional factors in critical periods in which the value of each yield-constitutional factor is determined, as seen in Table 1, the authors tried to establish some reasonable fertilizing methods to get good yields. The most effective stage for top-dressing to increase the value of each yield-constitutional factor was as follows (Refer to Fig. 1): (1) No. of panicles per hill……Maximum tillering stage. (2) No. of spikelets per panicle……Differentiating stage of 1st bract primordium and just before reduction division stage of P. M. C. (3) No. of spikelets per hill……Differentiating stage of 1st bract primordium. (4) Percentage of ripened grains……Just after full heading stage. (5) Weight of 1, 000 grains……Just before reduction division stage of P. M. C. The best top-dressing method to get good yields varied with the amounts of basic fertilizer and weather conditions, but it might be generalized that the top-dressing methods (Plot No. 3, 7, 4 and 5) which always cause the rice plant to increase the number of spikelets per hill or per unit area are successful in getting good yields under the conditions which make the plant get a high percentage of ripened grains, and on the contrary, the other top-dressing methods (Plot No. 6 and 1) which always cause the plant to get a high percentage of ripened grains are effective in increasing yields under the conditions which make the plant get an excessive number of spikelets per hill. And some other top-dressing methods (Plot No. 10, 9, 8, 2, 7, 4 and 5) which cause the plant to increase both the number of spikelets per hill and the percentage of ripened grain or only the number of spikelets per hill (except for Plot No. 3) were liable to get good yields under the conditions which make the plant get a medium percentage of ripened grains and a medium number of spikelets per hill.