Submitted to: Plant and Soil
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/26/2010
Publication Date: 6/24/2010
Citation: Bellaloui, N., Reddy, K.N., Abel, C.A., Gillen, A.M. 2010. Nitrogen metabolism and seed composition as influenced by foliar boron application in soybean. Plant and Soil. 336:143-155. Interpretive Summary: Boron is an essential nutrient for crop growth and seed quality. Low boron in soil leads to yield loss and low seed quality. Although the Mississippi delta soils contain enough boron to support soybean production, its absorption by soybean plants under drought and in nonirrigated fields may not be enough to support high production and seed quality. We found that two boron sprays increased protein content and decreased oil content. Two boron sprays also increased desirable effects of oleic acid and lowered linolenic acid in seed which could lead to improved stability and shelf-live. Soybean producers can spray boron under drought condition to gain the beneficial effect of increasing protein, increasing oleic acid and decreasing linolenic acid in soybean seed.
Technical Abstract: The effect of foliar boron (B) application on nitrogen metabolism and seed composition in soybean was not well investigated, especially under water stress conditions. Nonirrigated field experiment and watered (W) and water-stressed (WS) greenhouse experiments were conducted to investigate the effects of B on nitrogen fixation, nitrogen assimilation, seed yield, and seed composition. Boron was applied at a rate of 0.45 kg/ha once at 4 (T1) or 8 (T2), or twice at 4 + 8 (T3) weeks after planting (WAP). Control (C) plants received no B application. Under field conditions, the results showed that protein percentage was significantly (p< 0.05) higher and oil percentage was significantly (p< 0.05) lower in boron-treated plants with two B applications than the control plants. Boron concentrations in leaves and seed of B-treated plants were higher than those of control plants. Four times B applications resulted in a higher delta 15N (15N/14N ratio), indicating nitrogen fixation was substantially lower under multiple B-treated plants than under non-B plants. Higher oleic fatty acid and lower linolenic acid was observed in seed of plants that received two B applications. Similar trend of protein, oil, oleic and linolenic acids was observed in W plants under greenhouse conditions. In WS plants, however, boron concentration in leaves and seed were lower (ranges between 34-41 mg/ kg in leaves; 7-10 mg B/ kg in seed compared to the W plants (up to 70 mg B/ kg in leaves and up to 51mg B/ kg in seed). Nitrogen fixation measured using acetylene reduction assay (ARA) and nitrogen assimilation measured using in vivo nitrate reductase assay showed higher rate in plants that received either one or two B applications than the control plants. There were no differences in soybean yield between B-treated and B-nontreated plants. These results suggest that multiple foliar boron application at vegetative and flowering stages influenced seed composition and nitrogen metabolism, suggesting a possible role of B in soybean seed quality. Lack of B translocation from leaves to seed in WS plants indicated that B translocation to seed is significantly influenced by water stress even under adequate soil B concentration conditions.