Studies on the Effect of Internal Nitrogen Concentration of Rice Plant on the Constitutional Factor of Yield

Abstract

Effect of internal nitrogen level of rice plant on its constitutional factors of yield, namely the number of stems per plant, number of spikelets per panicle and weight of a grain, was investigated. Pot cultures of rice plant Norin No. 29 were divided into two groups which received different amounts of nitrogen fertilizer, i. e. heavy (H) and light (L) respectinely. At certain stages of their growth they were dressed with various additional amounts of nitrogen. By means of this procedure various grades of N-level in the plants were maintained, and, under such a condition the magnitudes of the yield constitutional factors were examined in relation to the N-levels in the plants. The results obtained may be described as follows : (1) Internal level of nitrogen at tillering stage presented distinct effects on tillering, correlation coefficient between the number of tillers per plant and N % of the leaf blade (this was employed as a indicator of nitrogen level in plant) being high, (H : r= +0.969 and L : r= +0.968) (Fig.2). (2) High correlation coefficients were obtained between the average nitrogen concentration during 7 to 28 days before heading and the number of spikelets per panicle of main stem, (H : r= +0.961 and L : r= +0.979). Regression equation was y=39.3x+7.1 for H and y=36.0x+17 for L, where y : number of spikelets per panicle of main stem, x : mean of N % of leaf blade during 7 to 28 days before heading. It can be understood from the above mentioned data, that the yield may be lowered strongly by deficiency of nitrogen in that particular period. (Fig. 3) (3) Extreme deficiency of nitrogen at the ripening period caused reduction of weight of a grain. The weight of a grain may be increased with the increase of nitrogen concentration in this low N % zone. But above certain critical concentration no such effect can be expected. It was observed that when nitrogen existed in excess, reduction in weight of a grain might take place. (Fig. 4, 5)