Evidence and perception of phosphorus loss risk factors in farmyards

Abstract

Farmyards present potential point sources of phosphorus loss to watercourses, affecting their ecological quality and attainment of environmental goals. Unlike many relatively simple point sources, farmyards are complex sub-systems within the wider agricultural setting, including individual runoff, management and infrastructure factors which influence the risk (likelihood and magnitude) of phosphorus loss. Comparison across these factors is confounded by heterogeneity in farmyard design and management, however, weighting of individual factors will support estimation of the relative riskiness of farmyards. This will allow identification of appropriate mitigation measures and evaluation of cost-benefit ratios. The aim of this study is to evaluate the riskiness of runoff, management, and infrastructure factors on phosphorus loss from farmyards to water, using expert opinion and to evaluate whether those estimates are supported by the literature. A survey of research, advisory and policy stakeholders was conducted (147 respondents) in which individuals rated the importance of individual factors from 0 (having no impact) to 10 (having critical impact) on phosphorus loss from farmyards. The most highly ranked factors were within the infrastructure category, followed by runoff and finally management factors. Factors relating to silage effluent and slurry storage were assigned the greatest risk (≥8.4). Runoff factors were also high risk but may be difficult to mitigate compared to infrastructure. Management factors were rated lower by all stakeholder groups but may offer low cost options to offset more intransigent risks. High consensus was observed between stakeholder groups, with significant differences in risk ratings for only 8 out of 29 individual factors.