EFFECT OF SOIL PROPERTIES ON THE SORPTION OF ORTHOPHOSPHATE AND PYROPHOSPHATE IN SOME ARID AND SEMIARID SOILS

The effect of soil properties on the sorption of orthophosphate (OP) a nd pyrophosphate (PP) was examined on surface (0-0.15 m) soil samples of Camborthids, Torrisamments, and Ustochrepts of arid and semiarid re gions of Haryana, India. Subsamples of each soil were equilibrated ind ividually for 24 hours at 25 degrees C with aqueous solutions of KH2PO 4 and K4P2O7 containing 0-100 g P m(-3), in a 1:20 soil : solution rat io. Percent sorption of added phosphate (X-ad) and distribution coeffi cients (K-d) progressively decreased with increasing solution P concen tration and sorption of phosphate (x). The values of X-ad and K-d for each soil were higher for OP than PP. Phosphate sorption was satisfact orily described by the Freundlich equation (r(2) = 0.96-0.99) and the two-surface Langmuir equation (r(2) = 0.95-0.99). The contribution of lower energy sites (b(2)) to total sorption maxima ranged from 97.4 to 99.4% in different soils, whereas the values of k(1), (binding energy constant of higher energy sites) were 58- to 598-fold of k(1) (bindin g energy constant of lower energy sites). The b(1) (sorption capacity of higher energy sites) and b(2) for OP were 1.18- to 2.11-fold and 1. 47- to 1.61-fold, respectively, as compared to their corresponding val ues for PP, whereas k(1) and k(2) were generally lower for OF. The eff ect of any individual variable soil property, such as clay, CaCO3, org anic carbon (OC), clay/OC, and CaCO3/OC, was marked on phosphate solut ion only on soils not varying in other properties. Nevertheless, the c orrelations of OC with b(1), b(2), and K, were positive and significan t (P = 0.05) owing to the positive correlations of OC with clay and Ca CO3. The Freundlich parameter K increased and n decreased with decreas es of clay and CaCO3.