From The Lexicon of Sustainability:

The soil food web is comprised of the species of organisms in our soil that create an environment free from disease, pests or fertility problems.  For Dr. Elaine Ingham, the result is healthy plants and a safer environment for us to live in. In parts of the world where human impact has been massive and un-remitting, especially in the case of over-reliance on petrochemical-based pesticides and fertilizers, we are losing many needed and necessary species of micro-organisms, putting our soil’s health at great risk.  The food we grow needs to contain balanced nutrition not only for humans, but also for the animals we care about and the life that sustains us.

(Learn more about the soil food web at the Lexicon of Sustainability)