Soil is a vast and complex ecosystem made up of plants, animals and micro-organisms. In any single cubic centimetre of soil, there are hundreds of millions of bacteria, tens of thousands of protozoa, hundreds of metres offungal hyphae and a host of other microbes and larger animals. Quentin Cooper talks to Dr Nick Ostle , from the Centre for Ecology and Hydrology in Cumbria, and Dr Richard Bardgett , from the University of Lancaster, about the secret life of soil. Producer John Watkins E-MAIL: material.world@bbc.co.uk