Application of different organic wastes in a soil polluted by cadmium: Effects on soil biological properties

The effects of adding a poultry manure (PM), a crushed cotton gin compost (CC), a sewage sludge (SS) and an organic municipal solid waste by-product (MSW) on the biological properties of a soil artificially polluted with cadmium (Cd) were studied. Soil samples were mixed with PM at a rate of 10%, CC at a rate of 17.2%, SS at a rate of 23.1% and MSW at a rate of 13.1% in order to apply the same amount of organic matter to soil. Soil enzymatic activities, nematodes abundance, earthworm weight, Cd concentration in earthworm tissues and Cd extractable in soils were measured at two different incubation times (3 and 90 days) in soils containing 0, 100, 250, 500 and 1000 mg Cd kg− 1 and in the same soils amended with PM, CC, SS and MSW. An unamended soil was used as the control. For non-amended polluted soils, the highest decrease of soil biological properties appeared at the highest rates of Cd at the end of the incubation period. For organic amended polluted soils, the inhibition percentage of soil enzyme activities and Cd concentration in earthworm tissues were lower than in non-organic amended soils, and nematodes abundance, earthworm weight increased than in non-organic amended soils. However, the inhibition percentage of soil enzymatic activities and nematodes abundance, earthworm weight, Cd concentration in earthworm tissues differed between organic matter amended soils. In this respect, at 1000 mg Cd kg− 1 soil and at the end of the incubation period, the Cd concentration in earthworm tissues, the enzymatic activities inhibition were lower in soils amended with MSW followed by SS, PM and CC, respectively, than in the non-amended soils. Also, the nematodes abundance and earthworm weight were higher in soils amended with CC followed by PM, SS and MSW, respectively, than in the non-amended soils. Since the adsorption capacity of Cd was higher in CC than the PM, SS and MSW-amended soils, the addition of organic wastes with higher humic acid concentration is more beneficial for remediation of soils polluted with cadmium.