Influence of Boron Sources and Application Levels on Fractional Distribution and Transformation of Boron in Calcareous Soil under Groundnut (Arachis hypogaea L.) Cultivation

Boron (B) dynamics in calcareous soils are strongly influenced by soil chemical properties, which affect its availability and transformation. A factorial experiment was conducted to evaluate the effect of boron sources (borax and boric acid) and application level (0, 2.5, 5, and 7.5 mg kg -1) on the distribution of boron fractions in calcareous soil under groundnut (Arachis hypogaea L.) at flowering, pod formation, and harvest stages. The results revealed that increasing boron levels significantly enhanced all boron fractions, including readily soluble, specifically adsorbed, oxide-bound, organically bound, residual bound, and total boron fraction, particularly at 7.5 mg kg-1, indicating greater retention and transformation into stable soil pools. In contrast, boric acid mainly increased the readily soluble boron fraction, contributing primarily to the immediately available boron pool. Boron fractions showed a progressive increase from the flowering to harvest, suggesting a gradual transformation from soluble to more stable forms over time. The findings indicate that borax promotes the transformation of boron into less available and more stable soil fractions, whereas boric acid enhances the readily soluble and plant-available form of boron in calcareous soil.