Fundamental Studies on the Ridge-Culture of Rice Plants : (4) Contents of Nitrogen and Carbondioxide in Soils, and the Plant Growth and Yields.

Abstract

This report deals with the comparison between the soils of two experimental plots, the ridge culture and level culture (the control) in respect to the contents of two forms of nitrogen (NH3 and NO3) and carbondioxide. At the same time, the growth and yields of rice plants grown there were also tested. The main results were as follows:- i) The decrease of NH3-N contents occured more rapidly in the ridge soils than in the controls for NH3-N was more exhausted in the former soils than in the latter. On the contrary, more NO3-N was found in the ridge soils than the controls. These facts might be due to the persistence of the oxidative layers in ridge soils. ii) More carbondioxide were therefore always found in the ridge soils than in the controls. iii) Plant height, tillers and nitrogen contents in leaf-blades surpassed in the ridge plots than in the controls. Above facts were observed during the vegetative growth period, from planting to the beginning of the differentiation of primordial ear. In the generative stage of the growth, however, this tendency became quite reversed. iv) In regards to the maximum length and dry weights of roots the ridge plots exceeded the controls during the whole course of the growth. But the top-to-root ratio was generally higher in the controls than in the ridges. v) The heading date seemed to be somewhat promoted in the ridge plots than in the controls. vi) Plants of the control plot were superior in grain weights per plant and number of grains per ear to those of the ridge plot. Especially the grain wieghts compared with the weights of culms and leaves were remarkably smaller in the ridge plots. vii) Here it might be said that the plant growth in the ridge plots looked just like that of the so-called Akiochi, which means the poor grain harvest in spite of the preceding vigorous vegetative growth. Consequently, in every year, 11∼23% decrease of yield per unit area appeared in the ridge plots compared with the controls. viii) In short, the vegetative vigor of plants of the ridge plots might be favoured by its better physical soil conditions during the vegetative growth period. But as plants developed into the generative growth, gradually the declination of vegetative growth is shown due to the nutritive deficiency occured in ridge soil. This nutritive deficiency was largely attributed to the striking development of the oxidative state in soils as already reported in the previous paper, and consequently caused the yield decrease.