Fate of heavy elements in sludge when applied to fruit trees.
Darwish O. H., Ahmed F. F., Mohamed G. A.
Author Affiliation: Soil Science Dept., El-Minia University, Giza, Cairo, Egypt.
Alexandria Journal of Agricultural Research 42 : 159-169
Abstract : The effects of sewage sludge application (5 kg/tree, applied in January) on yield and Cd, Se, Mn, Cr, Fe and Pb contents of leaves, fruit peel and fruit juice were determined for plants growing in 2 orchards in Mallawi district of El-Minia Governorate, Egypt. In the first orchard, grapes (cv. Red Roomy), Balady bananas, Balady oranges, Balady mandarins and Egyptian Balady limes were grown, while in the second orchard mangoes (cv. Hindy Bisinnara) and Balady guavas were grown. All plants received their N requirements from a combination of sewage sludge (55 g N/5 kg) and ammonium nitrate. Fruit yields were significantly increased by sludge application, most notably in grapes (69% increase compared with the control). Only very small amounts of each heavy metal were taken up by plants. The order of efficiency with which the plants took up elements from the soil was grapes > limes > mandarins > oranges > guavas > mangoes > bananas. Possible causes of the low uptake of heavy metals from the soil are discussed. Fe, Mn and Cr were present in leaves, fruit peel and fruit juice in higher concentrations than Pb, Se and Cd. Concentrations of heavy metals found in fruit juice were considered too small to be toxic to man.