The effects of sewage sludge applications on nutrient and heavy metal concentration in a calcareous soil

The objective of this study was to examine the effects of sewage sludge (biosolids) and barnyard manure on nutrient and heavy metal concentrations of calcareous soil at Van, Turkey and to estimate its ecological conditions during 2000 and 2001. Sewage sludge applied at five rates (0, 10, 20, 40 and 60 kg.tree(-1)) in an apple orchard on calcareous soil significantly increased the available "Olsen" P estimated by extraction with sodium bicarbonate, but also diethylenetriaminepentaacetate (DTPA)-extract-able Fe, Mn, Zn, Cu, Ni and total N, Zn and Cu concentrations at the end of the study. The pH of topsoil (0-30 cm depth) decreased from 8.6 to 7.8 at the highest application rate. Extractable P, Zn and total Zn and Cu concentrations of calcareous soil significantly increased at all depths in the profile. Sewage sludge application only increased total N, DTPA-extractable Fe and Ni concentrations of topsoil. Treatment with barnyard manure at one rate (25 kg tree(-1)) did not increase nutrient and heavy metal concentrations of soil as far as sewage sludge. Only DTPA-extractable Mn and total concentrations of Zn and Cu rose with manure application at the end of the experimental studies.