The Effects of Sewage Sludge Application Doses and Times on Extractable Metal Concentrations in a Calcareous Pasture Soil

Abstract

The objective of this study was to determine the effect of the increasing doses of sewage sludge and different application times on DTPA (diethylenetriaminepentaacetic acid) extractable nutrients and heavy metal concentration in calcareous soil for three years. For this purpose, sewage sludge was applied at different rates (0, 4.1, 8.2, 16.4 t ha-1) and periods (spring and autumn) to meet the nitrogen fertilizer requirement of grass-legume mixtures. Experiment results showed that cumulative sludge applications significantly increased DTPA extractable metal concentrations for 0-20 cm. Sludge application in spring period reduced the soil pH and increased the extractable metal concentrations compared to the autumn. Sludge application doses increased DTPA-Zn concentration for all soil depths and years. At the end of the experiment, it was determined that the heavy metal contents in the soil did not reach the levels that would have a negative effect on plant production. The fact that Van soil is rich in lime and alkaline pH of the soil, where the experiment was carried out, caused the solubility of heavy metals from sewage sludge to be low and toxic effect not to be seen. However, long-term sludge application should be followed in soil.