Nitrogen metabolism and seed composition as influenced by foliar boron application in soybean

The physiological effects of foliar boron application (FB) on nitrogen metabolism and seed composition have not been well established in soybean [(Glycine max(L.)Merr.)]. Therefore, the effect of FB on nitrogen metabolism and seed composition was investigated. Nitrate assimilation was evaluated by measuring nitrate reductase activity (NRA) and nitrogen fixation was evaluated by measuring nitrogenase activity and natural abundance of ¹⁵N/¹⁴N. NRA were significantly (P?≤?0.05) higher in plants that received FB than the control plants. Higher rate of FB (One application of four times of commercial rate) inhibited nitrogen fixation as measured by natural abundance of ¹⁵N/¹⁴N ratio, but increased NRA. The higher activities of NR and nitrogenase by FB were accompanied with a higher B concentration in leaves. The significant (P?15N/¹⁴N, accompanied with a higher rate of FB, suggested a possible mechanism where nitrate assimilation may compensate for the decrease in nitrogen fixation. FB increased seed protein by 13.7% and oleic acid by 30.9% compared to the control plants. This alteration was accompanied by a higher B concentration in leaves and seed. The results suggest that FB affects nitrogen metabolism and alters seed compositions, especially protein and unsaturated fatty acids.