LABORATORY STUDIES ON THE APPLICATION OF WHEAT-STRAW AND PIG SLURRY TO SOIL AND THE RESULTING ENVIRONMENTAL IMPLICATIONS

In a laboratory experiment, wheat straw (WS), pig slurry (PS) and a mi xture of the two materials (WSPS) were added to soil at the rate of 2% on a dry soil basis. Samples of the soil alone and with the amendment s were collected at various intervals of time during a one year period and analysed for: pH, electrical conductivity (EC.), NO3-, HPO42-, ph enolic compounds and volatile acids. A germination index (G.I) using t he Lepidium sativum test was carried out. The fractionation of the dif ferent forms of Cu and Zn was investigated. In comparison with the con trol, the WS-treated soil showed a constant diminution of NO3-, a slig ht lowering of pH and a net increase of EC. Sixty days after amendment , phenolic compound and volatile acid contents became equal to those o f the control, The WS did not show any germination effect and did not significantly influence the content and distribution of soil Cu and Zn . The addition of PS to soil produced an increase of EC., NO3- and HPO 42-,2-, with a consequent lowering of the pH, a moderate effect on phe nolic substances and volatile acids and a toxic effect on seed germina tion until the 7(th) day after the amendment. Total levels of Cu and Z n and their organic and inorganic bound fractions increased. The most consistent effect on soil properties from the WSPS mixture was for NO3 -, which was released slowly but progressively. This mixture increased the germination index in comparison with PS added alone to the soil.