The report, from University of Warwick HRI scientist Dr Rob Lillywhite, dismisses greenhouse gas emissions as a reason for reducing peat use, preferring the existing drivers of non-renewability and potential as a carbon sink.
It states: "In terms of total greenhouse gas emissions, the life cycle assessment approach supports the use of UK and Irish peat, and coir as growing media material.
"However, if the carbon neutrality of short-term materials and potential sequestration is taken into account, then the opposite is true and compost, timber products and coir are the preferred materials. These opposing conclusions suggest that further policy work is required."
It concludes: "The major driver for reduced peat use should remain its 'non-renewability' and potential for long-term carbon storage rather than its emissions of greenhouse gases."
The report highlights difficulties in assessing greenhouse gas emissions of organic materials because of a lack of data and confusion over whether to use weight or volume reporting units. It uses weight, which gives peat a poorer rating. The industry uses volume.
Growing Media Association (GMA) manager Tim Briercliffe said: "The GMA was included in the steering group for this project but expressed its concerns about the methodology and assumptions made throughout the process. The project was overambitious and set out to collate published information that unfortunately never really existed.
"The report acknowledges that frankly the project was unable to reach meaningful conclusions and the GMA would urge readers to approach it with caution. This work set out to understand important questions that the industry had raised. Unfortunately, we do not believe that this report enlightens the debate."
Former GMA chair Jamie Robinson added: "Like so much of the CO2 debate, there are a lot of questions on the methodology used and the conclusions are ambiguous - you can basically choose your outcome. I don't think that it takes the peat reduction debate any further forward."
But Vital Earth managing director Steve Harper said: "I think you need to take offsetting into consideration. Ultimately, if peat is undisturbed it is a carbon sink. If dug, it creates a footprint. If you can divert green and food waste from landfill, you reduce its impact on the planet (by not creating methane) and reduce waste and create a truly sustainable product."
A Defra representative said: "The research indicates that alternatives to peat are likely to have similar or lower greenhouse gas emissions associated with their production compared to peat - although the report does not consider specific products on the market, which are usually a blend of different materials.
"We are considering the development of a future policy to further reduce the horticultural use of peat. All evidence, including this newly published research, will feed into the development of the policy."
- The final report is available from www.defra.gov.uk
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UK peat greenhouse gas emissions (CO2)
Extraction & harvest 36kg
End of life 543kg
Carbon storage -136kg
Total CO2 emissions from other growing media
Green compost 12-93kg
Wood fibre -56-145kg