Evaluation of organic matter and nutrient composition of partially decomposed and composted spent pig litter.

Characterization of soil-applied organic material is necessary in order to clarify the nature of the organic matterand nutrients in it. In this study, the organic matter and nutrient contents of the spent pig litter (a mixture of partially decomposed pig manure and sawdust) was characterized before and after windrow composting to: (1) determine their changes during composting, and (2) assess the suitability of the composted spent litter as a soil amendment. Results demonstrated that the time required to reach maturity, and the composition of composted spent litter, depended on the chemical properties of the initial compost feedstock as well as the compost strategies used during composting. Total N, P, and K concentrations of the composted litter depended on chemical properties of the initial material. On the other hand, C:N ratio, humic and fulvic acid and cation-exchange capacity were influenced by differences in composition of the initial spent litter and composting strategy. If moisture content was maintained weekly at 60% with a four-day turning frequency, the litter reached maturity in 56 days. Maturation of spent litter was accompanied by a decline in total C, water-extractable metals, NH(4)(+)-N, increase in ash, (NO(3)(-)+NO(2)(-)-N, humic acid, humic acid:fulvic acid ratio, and cation exchange capacity, and elimination of phytotoxicity. The stability of nutrient and organic matter, acceptable pH and electrical conductivity values, and low levels of undesirable components such as heavy metals and phytotoxic compounds of the spent litter provided substantial evidence that agronomically suitable compost can be obtained after composting in windrows.