A pot experiment was carried out using boron-deficient alluvial soil to investigate the effect of boron on growth, yield and content of protein and fat in grains of soybean. 1) Visual symptoms were not observed in the boron-deficient plot until the period of terminal leaf development. 2) The color of the leaves remained green during the harvesting stage in the boron-deficient plot. Delay of maturity was clearly observed in the boron-deficient plot compared with the boron-treated plot. 3) Many sterile pods and immature grains were observed in the boron-deficient plot and yield of soybean was decreased to 67% of the boron-treated plot, resulting in a severe decrease in soybean yield. 4) Boron content of the grains of the boron-deficient plot was 4.2 mg kg^<-1> compared with 29.8 mg kg^<-1> of the boron-treated plot. 5) Decreases in the quantities of crude fat and crude protein were observed in the boron-deficient plot; especially, the crude fat quantity decreased remarkably. 6) In soybean grains collected from 36 different areas in Japan, a positive correlation was observed between boron content and crude fat content, but the correlation coefficient was low. However, among micronutrients, the boron content of grains showed the highest correlation coefficient to crude fat content. These results clearly show that not only yield but also the fat of grains is affected strongly by boron nutrition.
