Abstract
A combination of biological, chemical and physical properties and processes, together with the history and intensity of land use and management determine the forms, dynamics and mobility of phosphorus (P) in the soil-plant system. Amounts of total and available soil P in intensively managed agroecosystems have increased steadily since the early 1950s due to continued inputs of P, often in excess of crop requirements. The elevated P status of many agricultural soils has helped to sustain high levels of crop and animal production, although there is also an increased risk of diffuse P transfer in overland and subsurface flow. Rates of diffuse P transfer are generally small (1-6 kg P/ha/year), but this P loss can have a significant impact on water quality and health through accelerated eutrophication. Extensive research has been carried out to examine P mobility in soil and establish relationships between P inputs, soil P status and the amounts and forms of P loss to water. This in turn has resulted in the development of strategies for environmental management of P at the field and catchment scale. Phosphorus deficiency is not common in modern agriculture, although it could become an issue in reduced-input systems such as organic farming. Organic farming is expanding rapidly in many countries due to increased consumer demand for food produced with minimum inputs of synthetic soluble P fertilizers. Continued inputs of P in the form of imported feed, manure and sparingly soluble reactive phosphate rock should enable soil P fertility and productivity to be sustained in organic farming systems. Achieving the correct balance between maintaining productivity and minimizing P transfer will be a vital component of future strategies for effective soil quality management in low- and high-intensity agroecosystems. This in turn will require continued research to improve our understanding of the key properties and processes that determine the availability and mobility of P in the soil-plant system.