English abstract
Usage of sewage sludge for agricultural purposes is a common practice in many countries around
the world. It contains different nutrients and organic matter which are essential for plants. Besides, it contains different concentrations of heavy metals such as Cd, Cr, Mn, Pb and Zn. These heavy metals are essential for plants in trace amount and some are toxic even in small concentrations. Once these elements present in the soil, it would be difficult to get ride of them. Because they tend to accumulate on the soil surface or percolate to deeper soil layers causinganother problem which is ground water pollution The objectives of this study were to study the distribution of heavy metals (Cd, Fe, Mn, Pb, Zn and Ca and Mg) in sludge treated soil fraction, to detect the dominant element in sludge treated soil fraction, to compare heavy metals in the control and sludge treated soil samples and to assess heavy metals SCS concentration in the top and bottom soil layers. Open ended columns were filled with sandy loam soil to CON ins 45 cm high. Then 260 g of sewage sludge was added to three columns and another three columns were left as control. Distilled water was applied to the columns at a rate of 130 ml three days a week.Then after six months, soil samples were collected and analyzed by sequential extraction procedures and total extraction method. The results of this study showed that after sludge application, the concentration of Mn, Fe and Zn (in both layers) and Cd and Pb (in the top layer), were found in the residual fraction as dominant form. Cadmium and Pb in the bottom layer were found in carbonate fraction. Other elements such as Ca and Mg were not affected by sludge application they were in carbonate and exchangeable fraction, respectively, for both layers before and after sludge application. Thus, elements such as Ca and Mg were in available form to plants before and after sludge application while other elements such as Cd, Mn, Zn and Fe were not in available form because they were strongly bounded to the soil components. Lead on the other hand, tended to percolate to deeper layer of the soil because its concentration in the bottom layer was higher than in the top layer. Thu lead leached out from the soil to deeper layer with water application.
