Evaluating phytotoxicity of pig manure from the pig-on-litter system

摘要

The inhibitory effects of pig manure during in-situ composting in the pig-on-litter (POL) system, and during further composting in windrows were evaluated on seed germination and root elongation of selected plant species. Aqueous pig manure sawdustlitter extracts at different, stages of in-situ and further composting were incubated with different test seeds for five days in the dark, and the seed germination and root elongation were recorded. The seed germination percentage of the plants was not affected by the extracts during the first 30 weeks of in-situ composting hi the pig-on-litter system (POL), but was significantly affected thereafter. The root lengths of the plants were less than 50 percent of the control (deionized water) throughout theexperiment. Phytotoxicity of the extracts increased with age of pig manure because more salts, nutrients, and heavy metals, accumulated and imposed toxic effects on plants. To determine the elimination of phytotoxicity, the spent pig litter (collected after 13 weeks of in-situ composting) was stacked in windrows and composted for 91 days, and was examined for phytotoxicity. Results of the assay revealed that the phytotoxicity of spent litter was evident only during the early stage of composting. By day60, the germination index (GI) increased to over 80 percent. This increase corresponded with decreases in concentrations of NH_4~+-N, and water-extractable Cu and Zn of compost, demonstrating that these chemical compounds gradually disappeared during composting due to metabolism to other compounds and immobilization effects. The multiple regression analysis revealed that NH_4~+-N was the most important factors affecting the phytotoxicity of spent pig litter in the present study.