Soil organisms occur in immense variety and participate in very diverse soil processes. In natural ecosystems, soil biological processes recycle nutrients in vegetation types ranging from tropical rainforest to desert. However, at sites used for forest plantations or agricultural and horticultural production, nutrient cycling is unlikely to be sufficient to sustain the level of productivity required. Additional inputs are generally necessary to avoid nutrient deficiency, depending on the soil type and productivity level required.
How can these soils be managed to utilise the potential benefits from soil biological processes so that inputs can be minimised? Because soils throughout the world vary in their physical, chemical and biological states depending on their original level of fertility, the type and frequency of natural disturbances, climatic events and the nature of disturbances imposed by various land management practices, such management practices need to be flexible and founded on local knowledge.
Two complementary approaches are required to select the management practices that will maximise the contributions of beneficial soil biological processes to soil fertility:
• Selection of practices aimed at ensuring sustainable land use, based on knowledge of soil physical, chemical and biological fertility, so as to avoid future land degradation problems.
• Selection of practices aimed at rehabilitating existing degraded soils.
Soils are generally managed to produce a product that has a particular quality or use. If in the process, communities of soil organisms are maintained, the long-term productivity of managed ecosystems will be greatly enhanced. In the following sections, the effects of land management practices in a range of managed ecosystems are viewed from the perspective of soil biological fertility. Most land management practices indirectly manipulate soil organisms. A brief overview of the methods that have been used to directly manipulate soil organisms is also presented.