Nk. Tomar et K. Gautam, EFFECT OF SOIL PROPERTIES ON THE SORPTION OF ORTHOPHOSPHATE AND PYROPHOSPHATE IN SOME ARID AND SEMIARID SOILS, Arid soil research and rehabilitation, 12(3), 1998, pp. 263-273
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.