Varietal Differences in Nitrogen Response of Soybeans Associated with their Nodulation

Abstract

Experiments were conducted in order to determine whether varietal differences in nitrogen response of soybean plants were associated with their nodulation. For this study, four pairs of nodulating and nonnodulating soybean isolines (Tol-1 and Tol-0, A62-1 and A62-2, Norin No. 2 and Tozan No. 89, and T202 and T201, the former is nodulating and the latter is nonnodulating) in Experiment I and five nodulating soybeans (Koganedaizu, Norin No. 2, Orihime, Tachisuzunari and T202) in Experiment II were planted under sand culture conditions. Nutrient solution 500 ml containing sufficient quantities of essential elements except nitrogen were applied to each plastic pot filled with 4.5 kg sand twice every week during the growth period. The concentration of nitrogen in the solutions ranged from 12.5 to 400 ppm (Table 1). The following results were obtained. 1) At higher concentration of nitrogen, more vegetative growth and higher seed yield were obtained in nonnodulating soybeans except Tol-0. The maximum vegetative growth of Tol-0 was almost attained at 50 ppm nitrogen (Tables 3 and 4). 2) Each isogenic pair of nodulating and nonnodulating soybeans except a pair of Norin No. 2 and Tozan No. 89 showed no significant differences in vegetative growth and seed yield at 400 ppm nitrogen (Tables 2, 3 and 4). 3) More vegetative growth of nodulating soybeans except T202 and Tachisuzunari was observed at high concentration of nitrogen (200 and 400 ppm) than at low concentration of nitrogen (12.5 and 50 ppm) (Tables 3 and 5). Maximum seed yields of Tol-1 and A62-1 were obtained at 400 ppm nitrogen and that of Koganedaizu at 200 ppm nitrogen, while those of Norin No. 2, Tachisuzunari and Orihime at lower concentration of nitrogen than 200 ppm (Tables 4 and 6). The former varieties, which responded well to nitrogen application, had low seed yields at low concentration of nitrogen and did not surpass those of latter varieties even at high concentration of nitrogen. 4) Norin No. 2 and Tachisuzunari had more nodule number and dry weight at low concentration of nitrogen at early and late growth stages than the other varieties (Table 7). 5) The amount of accumulated nitrogen at the early pod filling stage increased with higher applied nitrogen concentration in all nodulating soybeans. At low concentration of nitrogen it was larger in varieties which did not respond well to nitrogen application than in varieties which responded well (Table 9).