Low molecular weight aliphatic acid contents of composted manures

Composted organic wastes improve nutrient availability by releasing organic compounds, particularly low molecular weight organic acids, which may affect nutrients availability in soils. In this study, composts were collected from different farms and industries across the Quebec Province (Canada). Low molecular weight aliphatic acids (LMWA) were extracted with water or Ca(OH)(2), and analyzed by ion chromatography. The main LMWA were acetic, formic, and oxalic acids. Small amounts of lactic, propionic, malic, citric, and aconitic acids were also found. The total amount of,vater-soluble LMWA ranged from 5.88 to 69.17 mmol g(-1). Compared with fresh manure, the quantities of LMWA decreased with composting time. The volatile aliphatic acids (VAA) accumulated in the early stage of composting while larger amounts of the nonvolatile aliphatic acids (NVAA) were found in the later stages. Turned and uncovered composts contained small amounts of LMWA. High amounts of LMWA were found in compost made with straw or wood residues. Land application of compost may introduce large amounts of LMWA to soils and strongly affect nutrient mobility and plant availability.