Effects of Nitrogen Application and Planting Density on the Growth and Seed Yield of Four Russian Varieties of Soybean (Glycine max L. Merr.)

N is the most crucial nutrient for plant growth and yield. Soybeans require a large amount of N for growth and seed production because of their high protein content. Soybean plants fix N2 by root nodules in association with soil bacteria, rhizobia, but both the fixed N and the N absorbed from roots are essential to obtain a maximum seed yield. However, excess or inappropriate N fertilizer application represses N2 fixation and reduces seed yield. A basal deep placement of lime nitrogen promoted soybean seed yield without inhibiting N2 fixation activity in Japan. This study aimed to evaluate whether this technology can be applied in the Far East of Russia. The effects of deep placement of lime N with a wide row (75 cm) on the growth and seed yield of four Russian varieties were investigated. Without N fertilization, the average seed yield in wide rows was 2.77 t/ha, which was not significantly different from that in narrow rows (2.39 t/ha). Deep placement of lime nitrogen with wide rows increased total mechanical seed yield by 38%, 53%, 17%, and 6% in Primorskaya 4, 13, 81, and 86, respectively. The effect of basal urea application in narrow rows varied among cultivars. Soil analysis and the N composition in xylem sap indicated that the Russian field is richer in soil N than that in Niigata, and the contribution of N derived from N2 fixation was lower than that in Niigata. The effects of row spacing and N fertilization on seed yield varied by variety; therefore, it is necessary to evaluate each variety to determine the optimal row spacing and N fertilization. The field experiment indicated that the deep placement of lime N promoted seed yield of Russian cultivars. This technique may be applied in soybean cultivation in a large field if the appropriate machine is available.