Soybean seeds contain a large amount of protein (about 35%), and there is a significant correlation between the total amount of N accumulated in soybean plants and seed yield. Soybean utilises N from several sources, including mineralised soil organic matter, symbiotically fixed N, and N from fertiliser when applied. Soybean plants fix a large amount of N by root nodules symbiotically associated with soil bacteria called "rhizobia". However, sole N2 fixation is often insufficient to support the vigorous vegetative and reproductive growth of soybean plants. For the maximum yield of soybean, it is necessary to use both N2 fixation by root nodules and nitrogen absorption from roots. This book introduces the promotive effects of deep placement of slow release N fertilisers on growth, N2 fixation activity and seed yield of soybean cultivated in some rotated paddy fields of Niigata prefecture, Japan, including rotated paddy fields and upland fields.