Strategies to reduce phosphorus loss in runoff from grassland based dairy systems

• Main Author: McConnell, Deborah Alison
• Published: Queen's University Belfast 2012
• Subjects: 628.16846
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579744

A decline in water quality, caused by elevated levels of phosphorus (P), has resulted in a loss of biodiversity in many freshwater ecosystems across Northern Ireland. Agriculture has been identified as the primary driver of P induced eutrophication of surface waters in Northern Ireland, accounting for almost 60% of P inputs to inland rivers and lakes. Following the introduction of the European Union Water Framework Directive (2000), action is now being taken to improve water quality in rivers and lakes within Northern Ireland. Whilst current mitigation strategies target reductions in P inputs to agricultural systems, there is also a need for on-farm management strategies which seek to reduce the risk of P transfer from agricultural land to receiving water bodies. Consequently the aim of this research programme was to identify management strategies to reduce P loss in runoff from grassland, with five field studies undertaken. These studies involved measuring P concentrations in runoff following the application of rainfall to hydrologically isolated plots. Experiment 1 examined the impact of early season grazing on soil-derived P losses to runoff while Experiments 2 - 5 examined different management factors affecting slurry associated P losses in runoff. These included investigating alternative slurry application methods, the timing of slurry application, the role of sward cover at slurry application, and the contribution of anaerobically digested slurry to P losses in runoff. The results from these studies highlight a number of on-farm mitigation strategies than reduce the magnitude of P loss in runoff. For example, limiting the duration of individual grazing bouts can be effective at reducing P losses in runoff while, the use of the trailing shoe slurry spreading technique, particularly at times of wetter soil and at higher herbage covers can significantly reduce P losses in runoff, relative to traditional splashplate spreading techniques.