Farming can be considered essentially as an ecological activity in which natural ecosystems open to influences of climate, soil processes and wild biota are modified to increase yields of desired food and fibre products. The greater the change to natural ecosystem the greater the human effort to maintain the agricultural system. It has been shown that conventional agriculture relying on tillage to enhance productivity results in greater ecological disturbance, and may be less sustainable in the long term compared to Low External Input Agricultural (LEIA) systems. LEIA systems are characterised by high genetic and cultural diversity, multiple use of resources and efficient nutrient and mineral recycling (Altieri 1987). There are many approaches to sustainable agriculture with the goal of reducing environmental degradation, through appropriate input technologies or farming techniques.
The search for biological alternatives to improve and maintain yields is becoming a high priority in view of increasing problems of pollution such as nitrate leaching into ground and surface water sources, soil degradation and productivity decline, disturbed hydrological regimes and major pest and disease outbreaks. In order to find alternatives for different environments and agricultural systems we need to understand the effect of different practices on soil organisms, their functions and processes and their influence on plant nutrition and soil stability. Understanding how agricultural management practices contribute to sustained fertility and productivity of arable soils requires knowledge of below ground food webs.
The importance of soil biota for sustaining the fertility and productivity of soils has also been the focus of several major programmes on the ecology of arable farming systems.
Agroecology and the farming systems approaches have greatly contributed over the last few years to the design of more sustainable and productive agro-ecosystems (Pimbert, Altieri, et al). More recently spatial statistics have been used to predict soils and regions within landscapes or fields that are more or less productive, helping farmers to decide where they should plant their crops and in what densities, and at what times of the year.
The biodiversity and agro-ecological revolution in agriculture should result in a definition of a set of new guiding principles and optimizing parameters for agricultural techniques. Alternative agricultural techniques, which aim for the preservation of biodiversity as well as productivity, should be able to balance their performance against existing ecological and socio-economic constraints.
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