EFFECTS OF COMPOSTING ON PHYTOTOXICITY OF SPENT PIG-MANURE SAWDUST LITTER

The phytotoxicity of spent pig-manure sawdust litter (spent litter) wa s evaluated during further composting. Aqueous extracts of the spent l itter were prepared by shaking the sample with water (1:IO w/v), and t he toxicity of these extracts was determined on relative seen germinat ion, relative root elongation and germination index (GI, a factor of r elative seed germination and relative root elongation). The sensitivit y of six plant species, namely Brassica parachinensis (Chinese cabbage ), Brassica albogalera (Chinese kale), Allium sativum (onion), Cucumis sativus (cucumber), Amaranthus espinosus (Chinese spinach), and Lycop ersicon esculentum (tomato) were compared. The effect of different moi sture levels during composting on the phytotoxicity of the spent litte r was also examined. Phytotoxicity of the spent litter was only eviden t during the earlier stage of composting (first 14 days) and, that see d germination and root elongation reached 100% (same as the control) t owards the end of the composting. The concentrations of the major inhi bitors, water-extractable Cu and Zn, and NH4+-N of the spent litter, d eclined during composting, indicating that these inhibitors were gradu ally eliminated as composting proceeded. Multiple regression analysis showed that the NH4+-N content of the spent litter was the most import ant chemical factor affecting phytotoxicity of the plant species selec tee for this study. Relative root elongation and CI were more sensitiv e indicators of phytotoxicity than seed germination. In the present st udy, the Gl's of all plant species were >80% at day 60, indicating tha t the spent litter had reached its maturation by clay 60. The response s of different plant species to the water-extracts of the spent litter were different. Among the six species, Chinese cabbage and Chinese sp inach were the most sensitive species, and tomato and cucumber were th e least sensitive species to indicate phytotoxicity of the spent litte r. Moisture adjustment during the composting process did not affect th e results of the phytotoxicity test. Copyright (C) 1996 Elsevier Scien ce Ltd