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PAM - Phosphate Acceptance Mapping

What is is Phosphate Acceptance?

Biosolids recycling

PAM - Phosphate Acceptance Modelling

Rock phosphate is a strategic, non-renewable, non-homogeneous natural resource that is essential to biological life. Biosolids (treated sewage sludge) contain usable quantities of phosphate, as well as nitrogen and other nutrients. In the UK recycling to land is considered to be the BPEO (best practical environmental option) and about 80% of biosolids (~820,000 tonnes) follow that route, although this constitutes less than 5% of the total organic material applied to land (Water UK 2006). The nutrient uptake of Phosphorous, (how much of the applied nutrient is used by plants), is generally considered to be lower than for other major nutrients such as Nitrogen. Uptake efficiency is, however, very variable; estimates range from over 90% where soil P is limiting but other nutrients are not (Johnston & Syers 2009) to very close to zero in soils with a high soil P-index. Over several years’ uptake efficiency on “typical” arable soils is likely to be around 30% (Sanders et al 2012, Syers et al 2008, Blake et al 2000).

Aubin et al (2002) identified seven main groups or categories of stakeholders concerned with economic, agronomic, environmental and public health aspects of the use of biosolids on land. In the UK two of these, the water industry and the British Retail Consortium, have jointly produced the “safe sludge matrix” and this voluntary agreement appears satisfactory to most other stakeholder categories. In some other countries in the EU recycling to land is much less common.

The provisional “phosphate acceptance mapping reported here” seeks attempts to identify areas where an application of biosolids would be economically and agronomically beneficial subject to the perceived constraints of different stakeholder categories.

PresentationsExplanatory Powerpoint and PDF presentations are online


The research described here was funded by the Natural Environment Research Council (NERC) under grant NE/M012794/1 ‘Enhancing nutrient use efficiency from biosolids for a resilient crop production system.


PAM Stakeholder Assessments

Representing a range of viewpoints

Stakeholder matrix

There are many different stakeholder groups and these will have different perspectives on what are the critical constraints in the application of biosolids should be. We have consulted with a sample of stakeholders as well as the Natural Environment Research Council (NERC) and the Sustainable Agriculture Research and Innovation Club (SARIC) (who funded this work under an “innovation grant”).

Five nominal groups of stakeholders were identified. A first group represents stakeholders who consider all factors to be equally important; the other four give respectively more weight to biodiversity, pollution or economic issues. Variants on the theme allowed for variation in the pollution theme between those concerned with protected area status, and those for whom soil erosion and heavy metal deposition to soil were the main concern.


PAM Stakeholder Group mapping

Representing a range of viewpoints

PAM - Phosphate Acceptance Modelling

A series of web mapping stakeholder dissemination tools are being developed and will shortly be made available here, that demonstrate, for each of the stakeholder groups identified, provisional phosphate acceptance maps across England and Wales.



The future for Nutrient Use Efficiency and Phosphate Acceptance

PAM - Phosphate Acceptance Modelling

Phosphate is a strategic non-renewable natural resource; the UK is heavily dependent on supplies imported from a single country (Morocco) and as alternative sources decline the worlds’ reliance on Morocco increases. Biosolids contain useful quantities of phosphate and reusing that resource in UK agriculture is considered to be the BEPO (best environmentally practical option). The nutrient use efficiency of Phosphate depends on many factors, but the principle advice appears to be to keep the concentration within the soil at some critical threshold. Concentrations above that level are likely to result in no observable increase in crop yield that is an apparent efficiency of close to zero. The critical threshold for cereal crop production should also be at a level where the risk of leaching and surface runoff will be minimal. In other parts of the EU real and imagined fears are restricting the rational use of biosolids either through outright bans or through excessively strict criterion on the constituents of biosolids. Biosolids are a heterogenous resource containing many components, this is a problem for those responsible for environmental regulation but the complete disassembly of biosolids into streams of pure elements seems unachievable at the moment. The representation of stakeholder groups presented above show how easy it would be to reduce the available “land bank” to an insignificant area and emphasis the need for continued dialogue and the need to resist “knee jerk” reactions to risk.

Specific conclusions include:

  • The provisional “Phosphate Acceptance Map” is a novel approach that makes use of national data sets and the results of field based experiments to identify areas where the application of biosolids would be agronomically efficient and least objectionable.
  • The Phosphate Acceptance Map considers soil, crop demand, climate, population density (as surrogate for supply of biosolids) and constraints such as erosion, biodiversity designation, landscape designation, pollution designation, distance and heavy metals. This approach was then combined with engagements with four stakeholders group which then provides a good holistic tool for end users such as water utilities, agronomist and farmers.
  • The representation of stakeholder groups presented above show how easy it would be to reduce the available “land bank” to an insignificant area and emphasis the need for continued dialogue and the need to resist impulsive reactions to risk.

Finding out more about PAM

Contact details

For further details concerning PAM and our nutrient use efficiency modelling research, please contact us:

Dr Ruben Sakrabani (project Principal Investigator)
Senior Lecturer in Soil Chemistry,
School of Energy, Environment and Agrifood
Building 52a First Floor Front Office, Cranfield University, Cranfield, Bedfordshire MK43 0AL
W: E:
T: +44 (0) 1234 750111 x2710

Research Co-Investigator was Dr Stephen Hallett, and PostDoctoral Fellow was Dr Richard Wadsworth