Analysis of Yield-Determining Process and Its Application to Yield Prediction and Culture Improvement of Lowland Rice : LXXVI. Responses of rice plants grown under different types of weather conditions to different fertilizing methods of nitrogen.

Abstract

With a view to clarifying the yield-determining process of rice and to improving the rice cultivation as well as its growth diagnosis, the authors examined the responses of rice plants grown under different types of weather conditions to different fertilizing methods. Dividing the whole growth period of rice plants into three periods, i. e. the first, second and third, and giving a favourable weather condition (non-shading treatment) or an unfavourable weather condition (shading treatment) to each period, thus creating 8 different types of weather conditions (See Table 1) through a whole growth period, and then applying 8 different fertilizing methods (See Table 1) to 8 different rice plants which were growing under 8 different types of weather conditions, the authors carried out the experiment in a paddy field in Konosu in 3 randomized replicates during 3 seasons (1959∼1961). As a result, in every fertilizing method 8 different types of weather conditions had come to be classified into 2 types, one is an increasing yield type and the other is a decreasing one, from the response of grain yield of rice plants to weather condition in the third period (ripening period), in other words, the weather condition in the third period (ripening period) was found to have the largest influence on yield, i. e. however long the period of an unfavourable weather condition might last before heading, if it was fine in the third period, almost no detrimental effect was found on the yield of rice, while however long the period of a favourable weather condition might last before heading, if it was unfavourable in weather condition in the third period, the yield of rice was markedly reduced. Furthermore, the worst or best fertilizing method was not found through all the types of weather conditions. Two fertilizing methods, however, i.e. all the amount of fertilizer applied basically (f1) and half applied basically and a half applied at full heading time (f6), are quite effective in increasing yield in most types of weather conditions, and these two fertilizing methods are both characterized by increasing the percentage of ripened grains. On the contrary, a fertilizing method, a half applied basically and half applied at the neck-node differentiation stage (f3), showed the lowest or near lowest yield in most types of weather conditions, and the fertilizing method was characterized by increasing the number of spikelets per unit area and by decreasing the percentage of ripened grains. These results can be considered to be ascribed to the fact that in the experimental field in Konosu the grain yield of rice is mostly influenced by the percentage of ripened grains and consequently the fertilizing methods which increase the percentage of ripened grains are usually much better in increasing yield than the fertilizing methods which increase the number of spikelets per unit area.