اثر لجن فاضلاب و pH خاک بر قابلیت جذب عناصر کم‌مصرف و فلزات سنگین

Excessive application of sewage sludge leads to the accumulation of potentially toxic elements in soils. The objective of this greenhouse study was to examine the DTPA–extractability of Fe, Zn, Cu, Mn, Pb, Cd, Ni, and Co in relation to soil pH and to investigate the concentrations of these metals in corn (Zea mayz). The study was conducted using a factorial experiment in a completely randomized design with three replications. Sewage sludge was applied at 0, 50, 100, and 200 t/ha on four soils [Langaroud (pH= 4.8), Lahijan (pH= 5.7), Rasht (pH= 6.8), and Isfahan (pH= 7.9)]. Application of sewage sludge significantly increased DTPA-extractable Fe, Zn, Cu, Pb, Cd, and Ni in all soils. The increasing effect was in accordance with sludge level. Langaroud soil had the highest and Isfahan soil the lowest levels of DTPA-extractable metals. Application of sewage sludge increased plant growth and metals in the foliage of corn plants. The metal concentration in corn tissues also increased with decreasing soil pH. Overall, the application of sewage sludge as an organic material, particularly in acid soils, may increase availability of heavy metals, which may, in turn, result in soil pollution. Therefore, addition of sewage sludge to soils should be managed on the basis of the changes in soil heavy metal concentration.