Composting Manure and Other Organic Materials

The Composting Process Composting is the aerobic decomposition of manure or other organic materials in the thermophilic temperature range (104-149oF). Composted material is odorless, fine-textured, and low-moisture. It can be bagged and sold for use in gardens or nurseries, or used as fertilizer on cropland with little odor or fly breeding potential. Composting improves the handling characteristics of any organic residue by reducing its volume and weight. Composting can kill pathogens and weed seeds. Disadvantages of composting organic residues include loss of nitrogen and other nutrients, time for processing, cost for handling equipment, available land for composting, odors, marketing, diversion of manure or residue from cropland, risk of losing farm classification, and slow release of available nutrients. During a three-year Nebraska study as much as 40 percent of total beef feedlot manure nitrogen and 60 percent of total carbon was lost to the atmosphere during composting. Runoff and leaching losses of sodium (Na) and potassium (K) were also high (above 6.5 percent each) during composting periods with high rainfall. Increasing the carbon-to-nitrogen ratio by incorporating high carbon materials (leaves, plant residue, paper, sawdust, etc.) can reduce nitrogen loss. In another study, a 30 percent reduction in nitrogenloss was found during composting of poultry manure in 55-gallon reactors when the C:N ratio increased from 15 to 20. Because of nitrogen, carbon, and potassium losses from manure during composting, it may be more desirable to apply the manure directly as a nutrient source unless there are concerns about improving manure characteristics, killing weed seeds and pathogens, or reducing odor problems.