Current Approaches and Future Trends in Compost Quality Criteria for Agronomic, Environmental, and Human Health Benefits

Organic wastes are composted to stabilize organic matter, reduce the moisture content, increase the concentrations of plant nutrients, eliminate pathogens and weed seeds, develop disease suppressiveness, and reduce greenhouse gas emissions. The requirements for compost quality depend on its final destination, which includes agriculture, horticulture, and urban landscaping. The development of a market for compost greatly depends on the definition and adoption of quality standards. Several countries and public and private organizations have established quality standards for compost, where certain properties are prioritized and different limits are established according to the end use. However, there is a need to harmonize such criteria at the international level. Also, if the process of composting is not managed properly, then it can result in excessive emissions of ammonia (NH3), nitrous oxide (N2O), and methane (CH4). This review compares compost quality criteria across different countries, addresses strategies for reducing the environmental impacts of composting processes, and evaluates new analytical and microbiological approaches to define compost quality. An overview of compost quality standards in Europe, China, and the United States of America is given, including a characterization of the plant residues, livestock manure, and organic wastes that can be composted.