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.

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 weatherconditions 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 weathercondition (non-shading treatment) or an unfavourable weathercondition (shading treatment) to each period, thus creating 8 different types of weatherconditions (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 weatherconditions, 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 weatherconditions 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 weathercondition in the third period ( ripeningperiod), in other words, the weathercondition in the third period ( ripeningperiod) was found to have the largest influence on yield, i. e. however long the period of an unfavourable weathercondition 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 weathercondition might last before heading, if it was unfavourable in weathercondition 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 weatherconditions. 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 weatherconditions, and these two fertilizing methods are both characterized by increasing the percentage of ripenedgrains. 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 weatherconditions, and the fertilizing method was characterized by increasing the number of spikelets per unit area and by decreasing the percentage of ripenedgrains. 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 ripenedgrains and consequently the fertilizing methods which increase the percentage of ripenedgrains are usually much better in increasing yield than the fertilizing methods which increase the number of spikelets per unit area.