GET REAL ABOUT AMMONIA
Rothamsted Research comments on the debate about ammonia emissions, calling for greater awareness of research done and practices already available to limit the pollution.
Last week saw the publication of the latest statistics on emissions of air pollutants in the UK, and covered the period from 1970 to 2016. They highlighted the increased contribution from the agricultural sector of ammonia, which stood at almost 90% in 2016 against a steady overall reduction from 1997 to 2013.
Ammonia gas is produced from livestock manures, particularly when spreading to land. When this reaches urban areas it can react to form harmful particles that can be breathed into our lungs. Deposition of ammonia can also lead to eutrophication, or excess nutrient levels, and acidification of terrestrial and aquatic ecosystems.
On Monday, 19 February, the BBC’s Farming Today programme looked at the issue, asking if muck spreading is making farming the villain of air pollution. (The subject was the first item on the programme, which is available here until 20 March.)
Mark Sutton, an environmental physicist at the Centre for Ecology and Hydrology, cited a number of reasons for the rise in emissions from farming, including the end of milk quotas in 2015 leading to an increase in cattle numbers.
More cattle are spending more time indoors, which means manure storage and spreading as opposed to grazing, noted Sutton. He also cited farmers’ increased use of urea as a fertiliser, which is cheap but has higher associated ammonia emissions.
Dairy Farmer Robert Craig from First Milk, one of the biggest milk suppliers in the country, owned by dairy farmers, said he found confusion in the science of ammonia reduction. Demand for cheap food is leading to further intensification of production of livestock, said Craig, who added that he felt there is little advice on what he should do as a farmer to reduce emissions.
Comment from Rothamsted Research
Tom Misselbrook is a biogeochemist in sustainable agriculture at Rothamsted. He is also lead scientist on the Defra-funded compilation of the ammonia and greenhouse gas emission inventory for UK agriculture.
“The industry views expressed on Farming Today hardly acknowledge the research that has been done and the engagement by scientists with the agricultural sector over the past decade.
“We have recently implemented an improved model to estimate ammonia and greenhouse gas emissions from UK agriculture, with better representation of UK soils, climate and agricultural practices, including the uptake of specific mitigation practices.
“Emissions arise predominantly from the management of livestock manures and from the application of synthetic nitrogen fertilisers, particularly urea fertiliser, which is associated with higher emissions than other types of fertiliser.
“The UK faces a great challenge in meeting internationally agreed ammonia emission targets for 2020 and beyond. As the major source of ammonia emissions, the agricultural sector is where reductions need to be made.
“What is now required is significantly greater uptake of mitigation methods, as set out by science, right across the sector. We have developed scenarios whereby the UK could meet future emission reduction targets and these have been discussed with industry and policymakers. There are cost implications, of course.
“UK and European research over the past 20 years or so has identified many potential mitigation methods, including low emission slurry spreading, such as shallow injection or band spreading, manure store covers and precision livestock feeding to avoid excess protein.
“We have provided policy and practitioner guidance, such as the Mitigation Methods - User Guide (Module 5 of Cost-curves for mitigating multiple water pollutants, ammonia and greenhouse gas emissions on farms, 2010) and the Options for Ammonia Mitigation: Guidance from the UNECE Task Force on Reactive Nitrogen (2014). (UNECE is the United Nations Economic Commission for Europe.)
“We have also been working closely with leading organisations of the agricultural sector, including the National Farmers’ Union, the Agricultural and Horticultural Development Board and the Agricultural Industries Confederation, and with government in developing strategies for UK agriculture.
“Improvements in production efficiencies, including targeted feeding of pigs and poultry, improved agronomy and the uptake of mitigation practices, albeit limited, have been offset by increasing urea fertiliser use, increasing livestock numbers and continued intensification of the dairy sector in particular.
“So, while the emission intensity of delivered products may have continued to decline, the total emissions associated with the agricultural sector have not.
“We will continue our research effort to develop cost-effective solutions that not only reduce ammonia emissions but also improve the nitrogen use efficiency within the farming system. And we will continue to seek to engage as strongly as possible with the sector in implementing these solutions.”
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