Author(s): R. KAR, P. C. BOSE AND A. K. BAJPAI

Abstract: Clay-organic complexes (COC) and organic-free clays (OFC) have been isolated from different locations under mulberry growing brown forest soils of Kalimpong. Homo-ionic suspension of isolated COC and OFC has been equilibrated with graded concentrations of phosphorus (P) at 300 ±1O K to study the adsorption pattern of the latter. The P adsorption data obtained for both the COC and OFC have been significantly fitted to Freundlich adsorption isotherm (R2 = 0.60* to 0.93**) while Langmuir adsorption isotherm is mostly fitted to the adsorption data pertaining to OFC (R2 = 0.82* to 0.99**). OFC registers higher strength of adsorption (K) and affinity of adsorbate to adsorbent (n) over COC in terms of Freundlich isotherm and thus confirms the positive effect of organic matter in association with clay towards the reduction of P fixation. Poor fit of Langmuir isotherm to the P adsorption data by COC corroborates the above finding. However, P adsorption by OFC in terms of Langmuir isotherm registers varying bonding energy (K) and adsorption maxima (b) for the soils of different locations. Interestingly, OFC isolated from the soils of Reshambari, Sangsey and Bhalukhop exhibit similar adsorption maxima but differentiate each other substantially in terms of tenacity for retention of P as evinced by varying K values. Attempts have also been made to relate the adsorption parameters with relevant soil characteristics.

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