Labile pool of cadmium in sludge-treated soils

The labile pool of cadmium in sludge-treated soils was determined by application of isotopic dilution principle under laboratory and green house conditions using moong (Phaseolus aureus L.) as test crop. The laboratory indices like isotopic distribution coefficient (Kd) of 115Cd in 0.1 M CaCl2, labile pool (LP) of Cd in DTPA–CaCl2–Na acetate (adjusted to pH 5.0, 6.0 and 7.0) and supply parameter (SP) using Kd as intensity and LP as capacity factor of Cd in soils, were computed to compare these values with actual uptake of Cd by the crop to test them as indices of Cd availability. The path-ways of transfer of soil Cd from the discrete chemical pools to plants were also computed. The LP (pH 7.0) and the SP were significantly correlated with the concentration of Cd in plants and its uptake by the crop. They are, therefore, good indices of Cd availability in sludge treated vertisol soils and can be used as reference indices for standarization of chemical extractants. The water soluble + exchangeable Cd and the 0.05 M EDTA extractable Cd were observed to be the two major chemical pools of Cd in soils responsible for supply of this element to plants. As substantial part of 0.1 M Na4P2O7 extractable Cd applied to the soils remains in same form, they are not transfered into the food chain. The amounts of soil Cd extracted by DTPA–CaCl2–TEA (pH 7.3), EDTA–NH4OAC (pH 7.3) and Mg(NO3)2 (pH 6.0) were significantly correlated with concentration of Cd in plants and with uptake of Cd by moong crop.