Biochemical and Microbial Characteristics of Mature Food and Animal Composts.

Studies of composted materials usually focus on the active composting phase and define maturity as the point where the product becomes stable. Compost stability has been correlated with a reduction in microbial biomass, a C/N ratio less than 25, reduction or change in odor, and reduced carbon dioxide flux among other parameters. The primary goal of composting is to convert organic waste products into humus or soil like materials. We investigated mature animal and food composts of various ages to evaluate their microbiological and biochemical soil quality characteristics. Compost samples of ages ranging from 6 mo. to 3 years were collected from composting operations in Kansas (food and greenhouse waste streams) and Tennessee (food, animal and bedding material waste streams). The compost piles were sampled by collecting a composite sample from each pile and the samples were analyzed for chemical, physical and microbiological properties. The total microbial biomass of the compost samples, as measured by PLFA analysis decreased with the age of the composts but remained above 4000 ng PLFA/g which is considered an excellent rating from a soil health perspective. Even though the Kansas composts had greater amounts of non-organic inputs (average 6.04% C compared to 12.44% C for the Tennessee samples) all samples had good to excellent soil quality indicators such as biodiversity and fungi to bacteria ratios.