Varietal differences in the response of rice plants to nitrogen-dressing with special reference to patterns of cange in nitrogen content of roots at successive growth stage.

Abstract

Varietal differences in the total nitrogen content of the roots or rice plants grown under 2 nitrogen dressing regimes (low fertilizer : 2.5 kg-N/10 a, high fertilizer : 7.5 kg/10 a) were investigated in 1984 by using the monolith method. Varietal differences in the decrease of the total nitrogen content of the roots and leaf blades as growth advanced were not recognized. The change in the amount of total nitrogen in the roots varied with cultivars. The cultivars used in this experiment can be divided into four types according to their patterns of change in the amount of total nitrogen in the roots, namely; a) those which showed no marked change in the amount of total nitrogen regardless of fertilizer levels and of growth stage, like Sen-ichi and Norin 3 (A type), b) those which showed a significant decrease in the amount of total nitrogen with the increase in the amount of fertilizer dressed, like Jyukkoku, Asahi and Futaba (B type), c) those which showed a proportionate increase with the amount of fertilizer dressed, like Takenari (C type), and d) those which showed variable response, where in the amount of total nitrogen was higher in the low fertilizer plot than in the high fertilizer plot in the early growth stage (July to August) and vice versa in the later stages (August to September) (D type). The general result of this study tends to suggest that there is a close significant correlationship between the amount of total nitrogen in the roots and root dry weight throughout the growth period of rice. Cultivars of A, B, and C types are distinct from each other on the regression line.