Carbon, nutrient, and mass loss during composting

Abstract

Hoop manure (a mixture of partially decomposed pig manure and cornstalks from swine fed in hoop structures) was the subject of a nitrogen mass balance during the feeding period. The manure was then composted in windrows to investigate C, nutrient, and mass loss during the composting process. Feeding cycle mass balance results indicated that N losses from the bedded pack ranged from 24 to 36%. Composting treatments included construction with and without a manure spreader and subsequent management with and without turning. Significantly greater losses of mass, C, K, and Na were found in the turned windrow treatment. However, composting in turned windrows proceeded at a much faster rate, with temperatures dropping out of the thermophilic range within 21 days. Composting without turning was less rapid, with temperatures remaining in the thermophilic range to the end of the 42-day trial. Mass reduction and C loss was significantly higher in the turned windrows than in the unturned windrows. Nitrogen loss was between 37 and 60% of the initial N, with no significant effect from turning. It appears that the low initial C:N ratio (between 9:1 and 12:1) was the most critical factor affecting the N loss in this composting process. Phosphorus, K, and Na losses were also high during composting, which could be due to runoff and leaching from the hoop manure. These elements may be significant contributors to surface and groundwater pollution through runoff and leaching. Additional research is planned to understand the extent of losses through volatilization, runoff, and leaching during composting.