Soil Boron Fractions and Response of Green Gram in Calcareous Soils

A greenhouse experiment with green gram on boron (B) deficient calcareous soils was conducted for two years at Ludhiana (Punjab), India to study soil B fractions and response of green gram to B application. Three soils with calcium carbonate (CaCO₃) content 0.8 (Soil I), 2.1 (Soil II) and 4.6 (Soil III) percent were collected from different sites of Ludhiana and Bhatinda districts, Punjab, India. The treatments comprised of five levels of soil applied B (0, 0.5, 0.75, 1.0, and 1.5 mg B kg^?1). The experiment was laid out in completely randomized design (CRD) factorial design with three replications. Readily soluble B comprised 0.39 to 0.76 percent in Soil I, 0.32 to 0.54 percent in Soil II, and 0.21 to 0.34 percent in Soil III of the total B, taking into account of all the levels of B applied at both stages of crop growth. Readily soluble B increased with increasing application rates of B and decreased from grand growth stage (40 days after sowing) to maturity of the crop. Specifically adsorbed, oxide bound, residual, and total B was higher in Soil III as compared to Soil II or Soil I. At maturity, specifically adsorbed B converted into other fractions to maintain equilibrium in soil solution. Organically bound B was greater than oxide bound B. Among all fractions, the residual fraction accounted for the major fraction of the total B. Soil application of lowest level of B was adequate to cause significant increase in dry matter yield and seed yield of green gram regardless of type of soil.