Soil Health and Related Eco-System Services in Organic Agriculture.

Soil health is dependent upon complex bio-physical and bio-chemical processes which interact in space and time. Microrganisms and fauna in soil comprise highly diverse and dynamic communities that contribute, over either short or long time frames, to the transformation of geological minerals and release of essential nutrients for plant growth. Certified organic soil management practices generally restrict the use of highly soluble plant nutrients, leading to dependence on nutrient sources that require microbial transformation of poorly soluble minerals. Consequently, slow release of nutrients controls the rate of uptake of nutrients by plants and associated plant physiological processes. Microbial and faunal interactions influence soil structure at various scales, within and between crystalline mineral grains, creating complex soil pore networks that further influence soil function, including the release of nutrients and their uptake by roots.  The incorporation of organic matter into soil as either manure or compost in organic farming systems is controlled to avoid excessive release of soluble nutrients such as nitrogen and phosphorus, while simultaneously contributing an essential source of carbon for growth and activity of soil organisms. The interdependence of many soil physical and chemical processes that contribute to soil health is strongly linked to activities of the organisms that live in soil as well as to root structure and function. Capitalizing on these contributions to soil health cannot be achieved without an holistic, multiscale, approach to nutrient management, an understanding of interactions between carbon pools and mineral complexes, and detailed examination of farm nutrient budgets.