Boron Fertilizer Effects on Soybean Yield, Leaf and Boron Concentration in Seed

Boron has long been recognized as an essential micronutrient for soybean [Glycine max (Merr.) L.]. However its primary role and mode of action remain unknown. Field studies were conducted on two soils(Byekola and Dashtenaz research station) in northeast Iran to determine the influence of B application time and rate on soybean growth, tissue B concentration, and seed yield. Boron fertilizer was applied at 0, 0.28, 0.56, 1.12, and 2.24 kg B ha-1 near the V2 or R2 growth stages. Boron fertilization had no significant effect on soybean yield at Dashtenaz but increased seed yields 47% at Byekola. B application at V2 increased yields compared with applications at R2. Trifoliate leaf B concentrations increased as B rate increased. Seed B concentrations also increased as B rate increased. Boron applied at the R2 stage resulted in equal or greater seed B concentrations than B applied at the V2 stage. Application of 0.28 to 1.12 kg B ha-1 during early vegetative or reproductive growth was sufficient to produce near maximal yields. The expected severity of B deficiency plus fertilizer and application costs associated with B fertilization should be considered when selecting the most appropriate B fertilization strategy.