WET SEWAGE SLUDGE APPLICATION EFFECT ON SOIL PROPERTIES AND ELEMENT CONTENT OF LEAF AND ROOT VEGETABLES

ABSTRACT

Pot experiments were conducted in a heated greenhouse to study the effects of increasing doses of sewage sludge application on vegetables grown for leaves (lettuce, endive, spinach) and roots (radish, carrots, beets), and on some soil properties. Results showed that sewage sludge application increased or decreased soil pH in cases of lower or higher values respectively, increased soil organic matter, and increased soil concentrations in all mineral elements studied, except for manganese (Mn) and cobalt (Co). Cadmium (Cd) was not detected in soil-sewage sludge mixtures. After sewage sludge application, edible plant parts of leaf and root vegetables had increased copper (Cu) and zinc (Zn) concentrations and decreased Mn concentrations, whereas iron (Fe) concentrations remained almost unchanged in the leaf vegetables and were lower in the root vegetables. Cobalt, lead (Pb), and Cd were not detected in plant tissues. Increasing doses of sewage sludge resulted in higher dry matter yield of vegetable edible parts, with those grown for roots responding stronger.

ACKNOWLEDGMENTS

Authors are grateful to Mr. G. Keskilidis, Director of sewage sludge treatment plant, Ptolemaida, Greece, for the stimulating discussions on these topics.