Effects of Soil Applications of Micro-Nutrients and Chelating Agent Citric Acid on Mineral Nutrients in Soybean Seeds

Micro-nutrient deficiency in soil results in crop yield loss and poor seed quality. Correcting this deficiency is normally done by foliar or soil application. The objective of this research was to determine the effects of soil applications of five micro-nutrients (Mn, Cu, Zn, Mo, and B) alone and in combination with a chelating agent citric acid (CA) on soybean leaf and seed nutrients. Source of micro-nutrient compounds were MnCl2, CuCl2, ZnCl2, MoO3, and H3BO3. Our hypothesis was that micro-and macro-nutrients may be transported to leaves and then to seeds at different rates. They may interact synergistically or competitively during the uptake process. A greenhouse experiment was conducted at Mississippi Valley State University, Itta Bena, Mississippi, USA. Soybean cultivar, Bolivar (maturity group V), was applied with micro-nutrients-chelating agent citric acid at V3 and R3 (pod initiation) stage. The results showed that applications of Cu, Zn, B and Mo increased three unrolled trifoliate leaves Cu, Zn, B by 26.5%, 13.8%, 113% and Mo increased to 179 mg/kg, respectively in the leaves. Also, the application of “Cu, Zn, B and Mo increased Cu, Zn, B by 55.5%, 8.2%, 28.6% and Mo increased to 202 mg/kg” respectively in soybean seeds. Application of Mn had no direct effect on increasing Mn either in leaves or in seeds, however, Mn and Mn + CA treatment affected other mineral contents. Application of Cu, Zn, Mo, B and CA increased macro-nutrients K, N, P, Mg, and S. Irrespective of the applications, the nutrient increase trend in seed was Na > Fe > Zn > Mn > B > Cu > Mo. However, Mo application resulted in the following seed nutrient accumulation pattern: Na > Mo > Fe > Zn > Mn > B > Cu. This may suggest that Mo had higher mobility to seeds than other micro-nutrients. Combination of soil application of Mo + CA increased Mo in leaves at V3 stage; however, Mo + CA soil application during pod-filling stage had no significant effects on Mo accumulation in seeds. The current research showed that some micro-nutrient application with the chelating agent CA could increase seed nutrients. Since these results are conducted under greenhouse experiments, further research under field conditions is needed before conclusive recommendations are made.