Phosphorus Fertilisation: Achieving Agronomic and Environmental Goals

Keywords: phosphorus, fertiliser use efficiency, soil test phosphorus, water quality, eutrophication, water framework directive.

On more intensive farms, an adequate soil P supply is critical for the production of high yielding grass and crops, particularly during crop establishment and early season growth. However, over and improper use of fertiliser inputs (especially phosphorus) to farmland can lead to reduced farm profitability and potentially negative effects on surface and ground water quality over time. Phosphorus transfers from soils to water needs to be minimised as it is a major cause of P-induced eutrophication in surface waters resulting in degradation of water quality and aquatic ecology resulting in negative environmental and economic consequences. The P attenuation capacity of different soil types can vary significantly which can affect the P availability and use efficiency of the P fertiliser applied. However, better knowledge of the P dynamics of different soil types would help to improve P advice and to target P fertiliser management appropriately. Soil P testing has been shown to be a good indicator of P availability and crop response to P fertiliser, and is an important tool for farmers to assess the fertility status of their soils and to plan an effective P fertiliser management strategy for their farms. Consideration should also be given to how fertilisers are applied to soils in order to maximise P use efficiency, especially on low P fertility soils. In recent years, increased awareness of environmental sustainability in agricultural systems has been a focus and is now being integrated more routinely to management practices on farms. Better P source management on farms with the aim of improving water quality is now an important concern for farmers as P use is currently curtailed by strict environmental legislation in some countries. This has encouraged the development of more sustainable approaches to P management to deal with the on-farm and off-farm impacts of P use. As the future of P fertiliser supply and price is uncertain, it is necessary to further develop our knowledge and management practices to maximise the efficiency of its use. The goal is to have better knowledge to help guide correct decisions to safeguard future grass and crop yield potential and economic viability of all farms and to minimise negative economic and environmental effects arising from its misuse.

D P Wall, Teagasc, Crops Environment and Land Use Programme, Johnstown Castle, Wexford, Ireland, and N T McDonald, Teagasc, Agricultural Catchment Programme, Crops Environment and Land Use Programme, Johnstown Castle, Wexford, Ireland.

28 pages, 8 figures, 3 tables, 60 references