It is universally recognized for improving soil structure and water-holding capacity. Compost helps the soil stay loose and easy to cultivate. Compost is, in fact, the end-product of the decomposition of organic matter. Making and using compost is also a way to recycle organic matter, especially materials that might otherwise have been treated as home or industrial wastes. In addition to soil improvement and the economic and social benefits of recycling organic matter, composting can provide other benefits.
Composts help fight soilborne pathogens that cause plant diseases.
However, not all composts are suppressive to all diseases. Compost, along with other organic matter, improves the capacity of soil to hold nutrients through a complex process called cation exchange capacity. In addition, compost indirectly provides nutrients for plant use when earthworms and other organisms digest the organic matter, producing nutrient-rich castings, or excrement. These products are significantly richer in nutrients than the surrounding soil, and in a form, which is readily available to plant roots. While compost provides small amounts of nutrients and makes other nutrients more available, it is not considered fertilizer.