Influence of sewage sludge application on soil quality: II. Heavy metals

In a 2 yr field experiment the influence of sewage sludge application on the total and available forms of heavy metals, i.e., Zn, Mn, Cu, Fe, Pb, Cd, and Ni was studied. The soil was a Typic Xerochrept and it was cultivated with cotton after amendment with sewage sludge rates ranging from 0 to 30-ton ha(-1)yr(-1). The experimental design was completely randomized blocks with five treatments each replicated four times. After 2 yrs of sewage sludge application, soil samples were taken from all the plots from a depth 0 to 50 cm and the concentrations of the total and available forms (DTPA extractable) of the above mentioned heavy metals were determined. The results showed that sewage sludge application significantly increased the total concentration of Cu, Zn, and Pb in the surface layer. DTPA exctractable forms were increased significantly in all the metals studied except Mn. Total concentration of Cu, Zn, and Cd were strongly correlated with organic matter content. DTPA extractable Cu, Zn, Cd, and Fe were also strongly correlated with organic matter content positively and negatively with soil pH. For all the metals studied except Cu and Fe, there was no evidence of leaching in the deeper layers.