Use of stabilised and dried sewage sludge in cultivation of maize for silage

The present study explores the effects of stabilised and dried sewage sludge obtained from Antalya Hurma Advanced Domestic Wastewater Treatment Plant on cultivation of maize for silage when applied to extremely calcareous, clay loamy soil at the doses of 0 (SS0-Control), 2 (SS2), 4 (SS4), 6 (SS6), 8 (SS8) ton da-1. The study was carried out in 4 repetitions according to a randomised block design in the form of field experiment. The sewage sludge was mixed homogeneously into the soil of the experiment parcels which were then irrigated equally by drip irrigation system and left to incubate for a period of 3 weeks. Following the expiry of the incubation period, maize seeds were sown. At the end of a cultivation period of 100 days, the plants were harvested and the experiment was ended. The soil and plant samples taken throughout the experiment were subjected to laboratory analyses. Application of sewage sludge slightly reduced the pH and concentration of exchangeable potassium (K), while increasing the concentrations of organic matter (OM), total nitrogen (N) and available phosphorus (P) in the growing media. Electrical conductivity (EC), exchangeable magnesium (Mg) and sodium (N) concentrations slightly increased, but exchangeable calcium (Ca) was not affected statistically. While DTPA-extractable iron (Fe) and zinc (Zn) concentrations of the growing media considerably increased, manganese (Mn) and copper (Cu) concentrations rose only slightly. DTPA-extractable lead (Pb) and chrome (Cr) concentrations could not be determined, as they were below the detection limits (DL for Pb < 0.03 mg kg-1; DL for Cr < 0.05 mg/kg) of the ICP-OES device, whereas nickel (Ni) and cadmium (Cd) concentrations increased slightly. The total P concentration of the cultivation media increased considerably, while the total K and Na concentrations increased only slightly. The total Mg and Ca concentrations decreased slightly. While the total Fe, Zn and Cu concentrations rose, the total Mn concentration was not affected statistically. The total Pb concentration could not be determined, whereas the total Cr and Ni concentrations decreased and the total Cd concentration was not affected statistically. With the application of sewage sludge, a considerable increase was recorded in the chlorophyll, total N, protein, P, Ca, Mg, Fe, Zn and Mn, and a slight increase was recorded in K, Na and Cu concentrations of the leaf samples taken midway through the cultivation period. While Pb, Cd and Ni concentrations in the leaf samples could not be determined, the Cr concentration was found to be not statistically significant. Nitrogen and protein exhibited a considerable increase in whole shoots (excluding cob), cobs and roots of the plant. In whole shoots, Ca, K and Fe concentrations decreased, Na, Zn, Cu and Mn concentrations increased, and P and Mg were found to have been not affected. While Cd in the top parts could not be determined, Pb, Cr and Ni exhibited a slight increase. In the cobs, P, Ca and Na increased slightly, but K and Mg were not affected. Fe, Zn and Mn concentrations in the cobs increased considerably, whereas Cu, Cr and Ni increased slightly and Cd and Pb could not be determined. In the roots, P, Ca, K and Na increased slightly and Mg was not affected. Fe, Zn, Mn and Cu concentrations rose significantly, whereas Pb, Cr and Ni increased only slightly and Cd could not determined. The application of sewage sludge increased the initial cob height and the number of cobs in the plant. The dry matter yield increased in whole shoots of the plants, but decreased in the cob. Moreover, a slight increase was recorded in the ADF and NDF content of the cob samples. The bioaccumulation factor (BAF) of Fe, Zn, Mn, Cu, Pb, Cr, Cd and Ni in the leaves, whole shoots and cobs of the plant is less than 1, suggesting no bioaccumulation. The bioaccumulation rankings of the elements are as follows: BAFZn>BAFMn>BAFCu>BAFCr>BAFFe (leaves); BAFZn>BAFNi>BAFCu>BAFCr>BAFFe (cobs); BAFZn>BAFMn>BAFCr>BAFCu>BAFNi>BAFFe (whole shoots). In conclusion, all doses of sewage sludge application benefitted the plant nutrition in the cultivation of maize for silage and did not cause accumulation of heavy metals. However, considering the risks that may occur during long-term use of this material, a dose of 2-4 tons da-1 could be recommended.