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 mixture 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 amendments were collected at various intervals of time during a one year period and analysed for: pH, electrical conductivity (EC.), NO 3, HPO42-, phenolic compounds and volatile acids. A germination index (G.I) using the Lepidium sativum test was carried out. The fractionation of the different forms of Cu and Zn was investigated. In comparison with the control, the WS-treated soil showed a constant diminution of NO 3, a slight lowering of pH and a net increase of EC. Sixty days after amendment, phenolic compound and volatile acid contents became equal to those of 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., NO 3 and HPO~-, with a consequent lowering of the pH, a moderate effect on phenolic substances and volatile acids and a toxic effect on seed germination until the 7 th day after the amendment. Total levels of Cu and Zn 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.