SOIL ORGANISMS AND SUSTAINABLE PRODUCTIVITY

The soil is a habitat for a vast, complex and interactive community of soil organisms whose activities largely determine the chemical and physical properties of the soil. In a fertile soil the soil biota may have a biomass exceeding 20 t ha-1, with life forms ranging from microscopic bacteria to the largest of earthworms which may be 1 m in length. Only a small fraction, probably <20%, of the soil microflora and microfauna (including bacteria, fungi, algae, protozoa, nematodes, collembola, acari) have been described. The role of soil organisms in the development and maintenance of soil structure, in nutrient cycling and in their various interactions (including associative, harmful and beneficial) with plant roots is described. Trophic interactions between soil organism groups in developed agroecosystems are considered in relation to nutrient cycling and the impact such interactions have on populations of saprophytic, parasitic and symbiotic microorganisms. Prospects for the management of the soil biota to promote sustainable productivity are illustrated by describing the effects of tillage on the composition of soil organism communities. Management technologies that conserve the biodiversity of communities may provide the greatest benefits for the long term sustainability of the soil resource.