EFFECTS OF SEWAGE SLUDGE ON NUTRIENT AVAILABILITY FOR KIWI FRUITS UNDER HIGH PH SOIL CONDITIONS

Abstract

A field experiment was conducted to investigate the effects of sewage sludge application on nutrient availability for kiwi fruits grown under high pH soil conditions. Solar-dried sewage sludge was applied (25, 50, 100, and 200 t/ha) at the beginning of the study. The considered soil properties (0-20 cm depth), pH, electrical conductivity (EC), organic matter, organic carbon, N, P, K, and cation exchange capacity (CEC) were determined. Micro-elements were analysed in the soil extracts for total and DTPA (diethylene triamine pentaacetic acid) values, in order to determine the elemental sufficiency of the sewage sludge incorporated in soil (application rate of 200 t/ha) which slightly decreased the soil pH from 8.2 to 7.8. Therefore, soluble macro- and micro-elements in all sewage sludge treatments were increased, relatively to the sludge dose, and sewage sludge application particularly increased the total element concentrations of Fe, Mn, Cu, and Zn to values above the deficient soil levels, at the highest application rates. Among the other elements, modest increases in total concentrations were observed; however, the recommended limits were not exceeded. Through the decreasing soil pH and the addition of trace elements, the application rates of 100 and 200 t/ha increased the availability of Zn and Cu upto 7 and 11%, respectively. As a result, the addition of municipal sewage sludge, at an annual application rate of 200 t/ha or less, can be used for kiwi fruit production on soilswith high pH values.