There are many different options to improve biological soil management. These include both direct and indirect interventions.

Direct methods of intervening in the production system attempt to alter the abundance or activity of specific groups of organisms (Hendrix et al., 1990). Examples of direct interventions include: (a) inoculation of seeds or roots with rhizobia, mycorrhizae, fungi and rhizobacteria, for enhanced soil fertility and (b) inoculation of soil or the environment with biocontrol agents (pest or disease) antagonists or beneficial fauna (e.g. earthworms).

Indirect interventions are means of managing soil biotic processes by manipulating the factors that control biotic activity (habitat structure, microclimate, nutrients & energy resources) rather than the organisms themselves (Hendrix et al., 1990). Examples of indirect interventions include most agricultural practices such as application of organic materials to soil, tillage, fertilisation, irrigation, green manuring and liming as well as cropping system design and management. More recent techniques include genetic control of soil function by manipulating resistance to disease, residue and rhizosphere quality (root exudates).

Some of these interventions, particularly direct ones, such as rhizobia inoculation in grain legumes, mycorrhiza inoculation for tree establishment and bio-control agents for disease and pest control are already well developed techniques, widely used by farmers in many developed and some developing countries. Nevertheless, these applications continue to be under-utilised in many less developed countries, particularly by resource-poor farmers. The potential for the use of these direct techniques is important and should be promoted by the relevant institutions and governments responsible for agricultural development.

Perhaps even great benefits, particularly over the long term, are likely to come from indirect interventions such as: choice of crops and their spatio-temporal organisation the enhancement of their natural ability to resist disease, improvements in the quality of the organic matter they produce, and by management of organic matter and other external inputs including fertilisers (TSBF, 2000).

Genetic manipulation of crops provides immense opportunities to improve their abilities to resist adverse environmental conditions (climatic, edaphic, biological), as well as improve the quality of the residues (above- and below-ground).

Tillage, monoculture, pesticide use, erosion and soil contamination or pollution generally have negative effects on most soil organisms, reducing the soil's capacity to maintain its function. This has numerous facets including decreased soil organic matter content, loss of soil structure, loss of soil through wind and water erosion, development of acidic, saline and sodic soils, and soil contamination with pesticide residues and heavy metals (Doran and Parking, 1994). On the other hand, the application of organic wastes, moderate fertiliser use, crop rotations, irrigation in dry and drainage in wet areas generally have positive impacts on soil organism densities, diversity and activity.

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