Phosphate Adsorption of Some Acid Soils in Relation to their Properties

摘要

Effect of soil properties on phosphate adsorption was examined on 14 surface (0-0.15 m) soil samples of Eutric Dystrochrepts and Mollic Udorthents from hilly area of Haryana; Typic Haplequolls, Aquic Hapludolls of U.P.; Typic Hapludalfs, Typic Haplustalfs, Typic Paleohumelts of H.P.; and unclassed soils of Assam. The samples of each soil were equilibrated for 24 hrs at 25±2QC with aqueous solution of KH_2PO_4 containing (0-500 mu g P mL~(-1)) in a l:20::soil:solution ratio. The amount of P adsorbedincreased and distribution coefficient (Kd) and percentage of added phosphate adsorbed (Xad) decreased with increasing solution P concentration. Phosphate adsorption was satisfactorily described by the two surface Langmuir (R2 = 0.97-0.99, P = 0.01) andFreundlich equations (R~2 = 0.97- 0.99, P = 0.01). The values of b2 (adsorption maxima of lower energy sites) were 2.82 to 8.78 folds as compared to bt (adsorption maxima of higher energy sites); whereas the values of kt (bonding energy constants of higher energy sites) were 4.58 to 51.99 folds of k_2 (bonding energy constants of lower energy sites). The contribution of high and low energy sites to total adsorption maxima ranged from 10.23 to 26.18 and 73.82 to 89.77%, respectively. Inverse relationshipwas observed between adsorption maxima and bonding energy constants. The pH was correlated negatively and significantly with constants of Langmuir (b_1, b_2, k_1) and Freundlich-K, while non-significantly with k_2 and n. The Al was correlated positivelyand significantly with b_1, k_1, k_2 and Freundlich-K but non-significantly with b_2 and n. The Al + Fe were correlated non-significantly with b_2, k_1, k_2, K and n, while significantly with b_1. The Fe and clay had nonsignificant correlations with allthe constants of Langmuir and Freundlich equations. However, when the effect of individual property (e.g. Al, Fe) was compared for soils, not varying in other soil properties, it was found to be highly marked. The multiple regression equations revealedthat soil properties (pH, EC, OC, CaCO_3, CEC, clay, Al, Fe and available P) jointly accounted for 73.80% variation in b_1, 64.30% in b_2, 73.0% in k_(l5) 43.0% in k_2, 85.30% for Freundlich-K and 26.40% for n in these soils.