Soil boron and its fractions in agro-climatic zones of Karnataka.

Abstract

The study was conducted to evaluate the distribution of native soil B fractions and to investigate their relationships to soil properties. 12 soils of surface as well as subsurface of 10 agro climatic zones of Karnataka with diverse properties were studied. The extraction scheme proposed here partitioned B into five pools, (i) readily soluble, (ii) specifically adsorbed, (iii) oxide bound, (iv) organically bound, and (v) residual boron, respectively extracted with 0.01 M CaCl2, 0.05 M KH2PO4, 0.175 M NH4-oxalate (pH 3.25), 0.5 M NaOH, and HF + H2SO4+ HClO4. Among the fractions, residual boron contributed around 98 per cent and ranged from 125 in central dry zone to 567 mg kg−1 in northern dry zone followed by oxide bound boron that ranged from 2.15 in coastal zone to 8.21 mg kg−1 in eastern dry zone and the least amount was readily soluble boronthat ranged from 0.03 mg kg−1 in southern transition zone to 0.78 mgkg−1 in northern dry zone. Total boron was in highest amount in northern dry zone (582.3 mg kg−1). Residual boron has minimum effect on available boron, whereas readily soluble boron, specifically adsorbed boron, oxide bound boron and organically bound boron contribute towards boron nutrition in all the agro climatic zones. Relationships of individual B fractions with physical and chemical properties of the experimental soils confirmed the general validity of the proposed fractionation scheme,which is satisfactory in terms of sensitivity and position for soil boron.