Biological indicators of soil quality inorganic farming systems

The health of the soil, recognized by its active role in the linked processes of decomposition and nutrient supply, isconsidered as the foundation of agriculture by the organic farming movement. Nutrient management in organically managedsoils is fundamentally different from that of conventional agricultural systems. Crop rotations are designed with regard tomaintenance of fertility with a focus on nutrient recycling. Where nutrients are added to the system, inputs are in organicand/or non-synthetic fertilizer sources that are mostly slow release in nature. Hence a greater reliance is placed on soilchemical and biological processes to release nutrients in plant-available forms. In this respect, nutrient availability inorganically farmed soils is more dependent upon soil processes than is the case in conventional agriculture. Thedevelopment and use of biological indicators of soil quality may therefore be more important in organic (and other lowinput) farming systems. The aim of this paper is to evaluate current evidence for the impact of organic farming systems onsoil biological quality and consider the identification of appropriate biological indicators for use by organic farmers andtheir advisors. Organic farming systems are generally associated with increased biological activity and increased belowgroundbiodiversity. The main impacts on biological fertility do not result from the systems per se but are related to theamount and quality of the soil organic matter pool and disruptions of soil habitat via tillage. Even within the constraints oforganic farming practices it is possible for farmers to make changes to management practices which will tend to improvesoil biological quality. It is, however, by no means clear that distinct indicators of soil biological quality are needed fororganic farming systems. It is important not only to identify the most appropriate indicators but also to ensure that farmersand land managers can understand and relate to them to support on-farm management decisions