THE ENVIRONMENTAL IMPACT OF PHOSPHORUS IN BIOSOLIDS APPLIED TO AGRICULTURAL LAND
Paul J.A. Withers1and Nicola J. Flynn2
1Catchment Management Group, ADAS UK Ltd, Gleadthorpe,
2Aquatic Environments Research Centre, Department of Geography, Whiteknights, University
of Reading
(free)
Practical guidelines on the sustainable recycling of phosphorus in biosolids to agricultural land
are required to minimise the risk of eutrophication of adjacent watercourses. A laboratory
incubation study showed that soils receiving biosolids that are now routinely ‘improved treated’ with iron (Fe) and lime have a low risk of dissolved P release to runoff even at application rates that exceed the current guidelines under codes of good agricultural practice.
Subject to field validation and further research, it was concluded that current guidelines
maybe unnecessarily restricting the amounts of biosolids that can be safely applied to
agricultural land, especially on soils with medium and high soil P sorption capacity.
Sustainable biosolid practice should take account of the site risk of P mobilization and
delivery in land runoff allowing more accurate decisions on biosolid type and rate according to
the degree of risk. In particular, tailoring the type and rate of biosolid according to the risk of
soil P release provides a more sustainable and flexible approach to biosolid recycling without
increasing eutrophication risk. Adoption of more sensitive land management measures may
also be required to reduce runoff and erosion risk in biosolid-amended fields with medium and
high connectivity to the watercourse.
KEYWORDS
Biosolids, phosphorus, agriculture, eutrophication, soil P saturation, runoff, erosion, risk
management
