Agronomic evaluation of dried sewage sludge and sewage sludge ash as sources of nutrients for maize

The aim of this study was to determine whether dried sewage sludge (SS) and sewage sludge ash (SSA) from municipal sludge processed in a mono-incineration plant in Olsztyn (Poland) are good sources of P and other nutrients for maize (Zea mays L.). The effect of fertilization with dried SS and SSA on heavy metal accumulation in soil and plants was also determined. The pot experiment comprised 9 fertilizer treatments: control; 12.5 g, 25.0 g and 37.5 g of SSA DM per kg soil DM: 12.5 g, 25.0 g and 37.5 g of SS DM per kg soil DM; 62.5 mg of P as Ca(H2PO4)(2) per kg soil DM; 62.5 mg of P as Ca(H2PO4)(2) + 62.5 mg of Mg as MgSO4 7H(2)O per kg soil DM. A dose of P as Ca(H2PO4)(2) covered the requirements of plants for P. In all the treatments, maize plants were additionally fertilized with equal amounts of N (as NH4NO2) and K (as KCl). Dried municipal SS and SSA were characterized by a high concentration of plant-available P, Mg and low concentrations of toxic trace elements, such as Cd. Pb, Ni, Cr and Hg. Fertilization with SS and SSA exerted a significant yield-forming effect. The weight of maize harvested from treatments fertilized with SS and SSA was approximately 5-fold higher than that noted in the control treatment. Sewage sludge ash and SS were very good sources of P and Mg for plants. The tested waste products significantly increased P and Mg uptake by plants and the content of available P in soil. Sewage sludge and SSA did not lead to a significant increase in heavy metal concentrations in soil or in plants.