A polyphasic approach for assessing maturity and stability in compost intended for suppression of plant pathogens

One of the most debated parameters surrounding the use of compost is the ability to evaluate maturity. Accurately determining maturity of composts is important in assessing application potential, including when considering compost as a suppressive agent to plant pathogens. In this study, methods to assess compost maturity and stability were evaluated on statically aerated composts known to be suppressants to turfgrass pathogens. Since disease suppressive capabilities of composts are related to microbial activity and microbial community structure, it is beneficial to monitor these components both during the composting process and in storage. Temperature and oxygen levels were useful in tracking progression of composting and assessment of compost maturity and stability. Physico-chemical variables monitored during composting and storage (nutrient levels (N, P, K, C), C:N ratio, dry matter, pH, and electrical conductivity) were indicative of some patterns. During storage of mature composts, oxygen consumption and carbon dioxide production were, indicative of maintenance of an active microbial population. Fluorescein diacetate (FDA) hydrolysis, monitored throughout composting and during storage, was indicative of maintenance of high rates of microbial activity, even during storage. Phospholipid fatty acid (PLFA) analysis was a valuable method for tracking microbial community profiles and metabolic rates during composting and in storage. Results were similar to respiration and FDA testing, in that they demonstrated a high level of microbial activity in composts. Development of composts for end-product uses such as plant disease and pathogen suppression requires monitoring of the composting processes to better understand progression of feedstocks into value-added materials. In addition, evaluation of storage capabilities of this ‘living’ material may aid in prediction of its useful life span as a disease suppressant.