2.2.2 Manure

Editor: Will Melling Writers: Bence Borbely, Trevor Chow, Tom Nott, Yang Zuo

annual or perennial legumes instead, and using those areas as pastures for cattle is a sustainable solution for restoring soil fertility and supplementing cattle’s dietary needs at the same time. As for cropping purposes, conclusive evidence shows that using legumes and the manure of grazing cattle instead of synthetic N fertilizers has a considerably lower global warming potential, milder N2O flux rates and more restrained nitrate leaching potential.79 In an experiment where N-fertility of several perennial pastures was supplied by N fertilizer for 5 years and then by alfalfa that was inter-seeded into the grasses, it was found that nitrate leaching was reduced by between 48 and 76 per cent when the N source changed from ammonium nitrate to alfalfa.80 Regarding benefits for grazing, legumes are an integral part of high-quality cattle forage. According to the Australian Department of Primary Industries, at least 30 per cent of a cattle’s diet should consist of legumes.81 These types of plants are very lowgrowing and tolerate close grazing. Legumes continue to branch and enlarge and eventually flower. Unlike grasses, legumes flower in the seeding year and several times annually every year thereafter.82

Suggestions:

• Subsidizing strategic rotational grazing practices on sheep and cattle farms under

Tier 1 of the Environmental Land Management scheme under the following conditions: ruminant farmers submit a comprehensive all-year grazing strategy, detailing the subdivision of pastures into paddocks, and the forage layout. Applicants need to provide photographic evidence for the presence of necessary infrastructure to their grazing strategy and document their compliance with the grazing strategy in the same manner. • Subsidizing mixed cropping and grazing enterprises under Tier 1 of the

Environmental Land Management scheme under the following conditions: a set minimum area of cropping land is used as a pasture paddock in the grazing-strategy submitted by the farmer. The concerned land area is planted with annual or perennial legumes such as alfalfa, red and white clovers, alsino etc. Subsidies are proportional to the area of land planted with legumes and grazed by cattle instead of being handled with synthetic N fertilizers.

2.2.2 Manure

Manure management is beyond doubt the second greatest source of methane emissions in the UK agricultural sector behind enteric fermentation, accounting for roughly 22% of

79T.E Crews, M.B Peoples, ‘Legume versus fertilizer sources of nitrogen: ecological trade-offs and human needs’ (Agriculture, Ecosystems & Environment, May 2004, Volume 102, Issue 3) https://reader.elsevier.com/reader/sd/pii/S0167880903003402?token=2A45FE223E1B84A4C9F9960FB6AEE9 5E06723255D2E4EBA2F175E2CA89C174257E3B74C848C740D1943FDCC6E7613949 80 L.B Owens, W.M Edwards, R.W Van Keuren, ‘Groundwater nitrate levels under fertilized grass and grasslegume pastures’ [1994] 81 Government of New South Wales, Department of Primary Industries, ‘Responsible, sustainable beef production’ <https://www.dpi.nsw.gov.au/animals-and-livestock/beef-cattle/husbandry/generalmanagement/production> accessed 12 January 2021 82 Dan Undersander, Beth Albert, Dennis Cosgrove, Dennis Johnson, Paul Peterson, ‘Pastures for Profit: A Guide to Rotational Grazing’ [2002] https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1097378.pdf

Editor: Will Melling Writers: Bence Borbely, Trevor Chow, Tom Nott, Yang Zuo

methane emissions.83 In addition, 6 per cent British agricultural nitrous oxide emissions derive from manure management.84 Although the role of animal dung and urine in UK agricultural GHG emissions is already substantial, what places manure management into the forefront of discussions about agricultural reform are its huge GHG reduction potentials. According to government estimates, 1.5 megatons of annual GHG reductions are achievable by pursuing environmentally sound manure management practices, and by 2018 only 0.04 megatons, about 2.5 per cent of this potential was actually realized.85

Anaerobic Digestion Anaerobic digestion is the process by which organic matter such as animal or food waste is broken down to produce biogas and biofertilizer. About 95 per cent of the aforementioned 1.5 megaton GHG reduction potential from manure management is attributed to anaerobic digestion. By 2020, only highly marginal results were achieved in this field, with 4 per cent of concerned farms using anaerobic digestion to process livestock manures and slurries in the UK.86

Biogas production is best suited for farms that collect manure as a liquid, slurry or semisolid; at a single point (a lagoon, pit, pond, tank or other similar structure), every day or every other day, which means that it is mostly applicable at confinement diary farms, and concentrated animal feeding operations (CAFO-s) for swine and poultry.87 Manure and slurry alongside other organic wastes first go through a waste handling system, then enter the anaerobic digester, where biogas is separated from other co-products. After leaving the Biogas Handling System, methane can be utilized to produce electricity via reciprocating engines or microturbines, heat via burning directly in boilers or heaters, and biofuel, transported in pipelines in compressed form.88 Anaerobic digestion is a highly efficient form of energy production from wastes, endorsed and supported by governmental policy with feed-in tariffs.89 Co-products such as digested solids can be applied as livestock bedding, or

83Department for Food, Environment & Rural Affairs, Agricultural Statistics and Climate Change [9th Edition, September 2019] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/835762/agricli mate-9edition-02oct19.pdf 84 U. Skiba, S. K. Jones, U. Dragosits, J. Drewer, D. Fowler, R. M. Rees, V. A. Pappa, L. Cardenas, D. Chadwick, S. Yamulki, A. J. Manning, ‘UK emissions of the greenhouse gas nitrous oxide‘ [5 May 2012] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3306628/ 85Department for Environment, Food & Rural Affairs, Greenhouse gas emissions from agriculture indicators: Slurry and manure [December 2020] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/945474/ghgin dicator-9slurry-18dec20.pdf 86IBID: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/945474/ghgin dicator-9slurry-18dec20.pdf 87 United States Environmental Protection Agency, AgSTAR, ‘How does anaerobic digestion work?’ <https://www.epa.gov/agstar/how-does-anaerobic-digestion-work> accessed 12 January 2021 88 IBID 89 Office of Gas and Electricity Markets, Feed-In Tariff (FIT) rates [March 2020] https://www.ofgem.gov.uk/environmental-programmes/fit/fit-tariff-rates