Composting and compost utilization for agronomic and container crops.

Abstract

Stabilization of organic wastes by composting is highly desirable as composting eliminates odor, increases nutrient contents, and prevents the organic wastes from becoming phytotoxic when incorporated into the soil. It is a microbial-mediated process, which breaks down some of the organic N to more readily useable forms, with the release of a sizable portion of organic C as CO2. The viability of composting depends very much on the quality and consistency of compost produced as they affect compost marketability and its end use. The article reviews the composting processes, various techniques used in compost production, and the methods used in the determination of compost maturity and quality. The selection of a technique and a location for composting should consider the availability of feed stocks and the land, and the proximity to urban population. The review also focuses in some detail on nitrogen and the ratio of carbon to nitrogen in various composts and how effective the composts are in promoting crop productivity and soil quality as well as in replacing peat as a growing medium for container crops. Because of a significant impact of compost metals on compost quality and soil metal accumulation, an extensive review was made on the concentrations of various metals in composts using municipal solid waste and/or sewage sludge (or biosolids) as feed stocks. The concentration limits of various metals in the finished composts imposed by different countries around the world and the resulting effect of compost application to soil on plant uptake of metals and the transferability of the added compost metals from soil to plants were discussed.