The Fate of Fertilizer Nitrogen Applied to the Paddy Field and its Absorption by Rice Plant : VII. Relationships between the absorption of nitrogen by the rice plants and the growth of the plants

Abstract

Field experiments were carried out in order to study the relationships between the nitrogen absorption by rice plants grown under various cultural conditions and the growth of the plants. The results obtained are as follows; 1) It was found that the rate of nitrogen absorption by the rice plants was the greatest just before the neck node differentiation stage throughout all the growth stages. The greatest rate of nitrogen absorption by the plants at this stage was positively correlated to the length of culms, the sum of lengths of lower three internodes, the sum of lengths of upper three leaf blades (excepting those of the plots of nitrogen top-dressing), and the number of spikelets per panicle (excepting those of the plots of no basal nitrogen, nitrogen top-dressing at the neck node differentiation stage and at the stage of reduction division), respectively. 2) The amount of plant nitrogen per unit area at the early stage of spikelet differentiation was positively correlated to the number of panicles per unit area. Furthermore, the amount of nitrogen in plant per unit area at the ear mergence was positively correlated to the number of spikelets per unit area. 3) It was previously shown by Matsushima et al (3, 4, 5, 6) that lodging resistance and light utilizing efficiency of rice plants were improved by the decrcase of the length of culms, the sum of the lengths of lower three internodes, the sum of the lengths of upper three leaf blades and the number of spikelets p6r panicle and by the increase of number of panicles and spikelets per unit area. In order to obtain the growth of rice plants mentioned above, the rate of nitrogen absorption by rice plants must be decreased just before neck node differentiation stage and be increased at the other growth stages. It was recognized that early transplanting and high plant density was effective means to permit the desirable rate of nitrogen absorption by rice plants and to increase the rice yield per unit area.