Soil Ecology and Soil Health.

The soil provides habitat for myriad organisms of different type, size, and physiological activity.  Their activities, which are integral to the ecosystem functions of a healthy soil, include the decomposition of organic materials, sequestration and mineralization of nutrients, facilitation of access of organisms to new resources, improvement of soil structure for percolation and penetration, biodegradation of contaminants, and regulation and suppression of opportunistic pest species.  In many cases, the productivity of managed systems has been developed through manipulation of the chemical and physical components of the soil, with consideration of the biological component mainly focused on those species that are detrimental to productivity.  Often that focus has resulted in soils which support high crop productivity but which are quite unhealthy from the standpoint of their ecological functions; their productivity requires a continuous or frequent input, which may be environmentally and economically unsustainable.  Once a desired ecosystem function is not performed by any of the contributing species, the soil is no longer healthy relative to that function.  Biodiversity provides a greater range of organism types and adaptations contributing to each ecosystem function and consequently increases the range of conditions in which the function is performed, the magnitude of the function and the health of the soil.  The challenge in soil management is to promote and maintain the beneficial functions of the soil biota.  Nematodes are convenient bioindicators of soil condition; they contribute directly to ecosystem services and are indicators of the presence and activities of other organisms.  As representatives of the resident biota, nematode assemblages indicate three attributes of the biological component of the soil: the nature of ecosystem services available, the magnitude of those services, and the complementarity of services across time, space and microhabitat.  Current and anticipated advances in molecular techniques for determination of nematode abundance, diversity and function will facilitate application of bioindicator-based measures of soil health.