Soybean is very important leguminous crop world wide supplying protein and oil for food and animal feed. Soybean requires a large amount for N for the seed production because protein concentration is very high compared with cereals about 40% based on dry weight. Soybean plants assimilate the N from three sources; N derived from symbiotic N₂  fixation by root nodules with soil microorganism bradyrhizobia, absorbed N from soil mineralized N, and N from fertilizer when applied. Sole N₂ fixation is often insufficient to support the vigorous vegetative and reproductive growth. On the other hand, a heavy supply of N fertilizer depresses nodule development and N₂ fixation activity, which sometimes results in the reduction of seed yield. Our group (Niigata Agricultural  Research Institute and Niigate University) have developed a new fertilization technique for soybean cultivation to supplement N during seed filling stage without concomitant depression of  N₂ fixation by deep placement (20 cm depth from soil surface) of slow release  N fertilizers, coated urea and lime nitrogen (calcium Cyanamide) The N  from coated urea was efficiently supplied (the recovery rate was about  60 % by ¹⁵N experiment) mainly during reproductive stage without depression of N₂ fixation activity which was monitored by simple relative ureide method. We analyzed the  beneficial effects from soil analysis and plant nutrition sides. We would like to introduce the outline of our study  and review the characteristics of soybean N nutrition and N  fertilization to promote high and stable soybean seed production.