Compost is made through the aerobic digestion of organic residuals by natural micro-organisms.  The composting process leads to the recycling of many types of organic materials, some of which are considered wastes.  By stabilizing the material and reducing its volume, composting then produces a value-added end product, compost. This is material is useful as a soil amendments that provides stable carbon as well as slow release nuntrients which in turn can lead to soil quality improvement, better crop performance, and fewer undesirable environmental impacts.

Composts are a diverse material.  The end properties of a compost depend on many factors – initial feedstocks; type of composting process; weather; maturity and aging, to name a few.  The properties of the compost dictate its most appropriate end use.  Some composts are high carbon and low nutrient, which may be suitable for soil reclamation where high rates can be used with minimal risk of nutrients causing environmental contamination.  Others are high nutrient, and need to be used carefully to avoid excess nutrient build-up.  Composts can contain unwanted contaminants that should be avoided such as high levels of heavy metals, stable herbicide residues, plastics and other garbage.  Very high salt content in some composts can damage crops and the material should be used sparingly and without direct contact with roots.  Thus, there are many considerations in using composting to process organics and making a compost suitable for different markets.

WSU has done extensive research on compost over the years, including studies of nitrogen mineralization, fate of herbicide residues, using composting to process livestock mortalities, and potential benefits from compost for crop production and soil condition.  See the web pages below for specific resources.