Abstract
Incubation and field experiments studies were carried out to estimate urease and arginine ammonification activities in soil treated with sewage sludge as bioindicators. The amounts of DTPA extractable Cd, Cr, Cu, Pb, Ni, and Zn in the original soil were 0.03, 0.64, 5.3, 2.3, 0.35 and 1.3 mg/Kg, respectively. The incubation study was carried out in the laboratory at controlled conditions (23 +/- 3 C degrees and 50 % water holding capacity) at different periods. The obtained results showed that urease and arginine ammonification activities increased with increasing sludge in soil relative to the control soil. In experimental field study, soil samples (0-15 cm) were collected from fields cultivated with winter season as wheat and faba bean and summer season crops as corn and soybean. The results obtained showed that urease and arginine ammonification activities were higher in sewage sludge-treated soil than in those of the control. Urease and arginine ammonification activities were almost lower in soil samples collected from fields cultivated with winter crops than those of summer crops. These data showed that the amounts of DTPA - extractable Cd, Cr, Cu, Pb, Ni, and Zn from the sludge treated soil of the four fields did inhibit both urease activity and arginine ammonification. These findings suggest that recycling of sewage sludge, and applied at a rate of 200 ton /hectare for three successive growth seasons did not lead to accumulation of heavy metals in soil to the levels which could hinder soil biochemical activity.