How is methane produced in agriculture


The biggest source of agricultural methane emissions is enteric fermentation , which is the digestive process by which microbes in the guts of ruminant livestock break down plant matter, enabling it to be absorbed into the animals’ bloodstream, and producing methane as a by-product.Jun 10, 2019

How much methane is produced by agriculture?

36.2 percentHowever, the emissions profile for agriculture differs from that of the economy as a whole. U.S. agriculture emitted an estimated 698 million metric tons of carbon-dioxide equivalent in 2018: 12.3 percent as carbon dioxide, 36.2 percent as methane, and 51.4 percent as nitrous oxide.

Is methane gas produced from agriculture?

Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices, land use and by the decay of organic waste in municipal solid waste landfills.

How is methane produced in soil?

Methane is produced in soils as the end product of the anaerobic decomposition of organic matter. In the absence of oxygen, methane is very stable, but under aerobic conditions it is mineralized to carbon dioxide by methanotrophic bacteria.

What are sources of methane production?

Methane is emitted from a variety of anthropogenic (human-influenced) and natural sources. Anthropogenic emission sources include landfills, oil and natural gas systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial processes.

Which crops produce the most methane?

All pieces are based on research being conducted for the 2013-2014 World Resources Report. Rice is the nutritious staple crop for more than half of the world’s people, but growing rice produces methane, a greenhouse gas more than 30 times as potent as carbon dioxide.

Do plants take up methane?

In addition, plants take up and transpire water containing dissolved methane, leading to the observation that methane is released. Together with a new analysis of global methane levels from satellite retrievals, we conclude that plants are not a major source of the global methane production.

Does soil capture methane?

As soil moisture increases, less methane is able to diffuse into the soil from the atmosphere, Groffman explains: “Increased soil moisture inhibits diffusion of methane from the atmosphere into the soil, which reduces the ability of bacteria to access and consume the methane.”

How can we reduce methane emissions from rice cultivation?

A major source of methane emissions is the decomposition of fertilizers and crop residues in flooded rice cultivation. The most effective option to reduce these emissions would be to prevent submergence of rice fields and to cultivate upland rice or other upland crops.

What are the top 3 sources for methane emissions?

The major sources of U.S. methane emissions are energy production, distribution, and use; agriculture; and waste management (Figure 17).

What are two natural sources of methane?

Methane Emissions: Natural Sources Wetlands, termites and the oceans are all natural sources of methane emissions. The methane produced by natural sources is completely offset by natural methane sinks. This has been so for thousands of years.

How do wetlands produce methane?

In wetlands, methane is produced from microbial activity. Once it’s produced, there are multiple pathways in which methane is consumed and transported from the soil to the atmosphere: plants, bubbling, and diffusion.

How is methane generated?

Methane emissions are generated by a number of processes, both natural and resulting from human activity (‘anthropogenic’). Most natural methane emissions arise from microbial decomposition of organic material (for example, decaying plants) in anaerobic (‘lacking oxygen’) conditions in wetlands. There are a number of sources …

What is the main source of methane?

The biggest source of agricultural methane emissions is enteric fermentation, which is the digestive process by which microbes in the guts of ruminant livestock break down plant matter, enabling it to be absorbed into the animals’ bloodstream, and producing methane as a by-product.

How much methane is oxidized?

A smaller proportion (8%) of methane is also oxidised by OH radicals in the upper atmosphere (‘stratosphere’); there is also thought to be an additional small amount of removal (around 4%) of atmospheric methane by reaction with chlorine radicals.

Is methane from agriculture the same as fossil fuel?

Importantly, this also means that methane from agriculture is different from fossil fuel methane (see above), because for fossil fuel methane this CO 2 is an additional input to the atmosphere, which had previously been locked away underground 2.

How much methane is broken down?

Approximately 95% of the methane is ‘removed’ or broken down in the atmosphere itself. Most of this (84% of total removals) is in the lower atmosphere (‘troposphere’), and results from a reaction with hydroxyl (OH) radicals – highly reactive molecules that play an important role in the removal of many other atmospheric pollutants in addition to methane. Ultimately, as a result of this process, much of the methane is broken down into CO 2. However there is still some scientific uncertainty over exactly how much of the methane is finally converted to CO 2 and how much might remain as other intermediate carbon-containing compounds without a significant direct effect on the climate 4 .

How long does methane last?

This is particularly important for methane, as it is a relatively short-lived GHG, with emissions breaking down after an average of around 10 years. In contrast, a significant proportion of our CO 2 emissions are expected to persist in the atmosphere for centuries, or even longer.

Does methane increase atmospheric concentration?

And increasing methane emissions result in increasing atmospheric concentrations. Since methane has a powerful effect as a greenhouse gas, even relatively small increases in concentration can have a major climate impact, making the recent observations of increasing atmospheric methane highly concerning.


Cows, sheep and goats are ruminant animals, meaning they host millions of tiny microbes in their stomachs which aid in digestion. While these bacteria are helpful to the livestock’s health, an unfortunate by-product of their functioning is the creation of methane gas, which is expelled into the atmosphere through the animal’s mouth and rear end.

Stubble burning

Stubble burning refers to when farmers intentionally burn off the crop residue which remains behind after the previous yield has already been harvested. It is done to remove herbicide-resistant vegetation, deter termite infestations and ready the terrain for the coming season.

Rice paddies

Cultivation of rice is a staple of the Asian diet and in fact, scientists believe that they can track the practice back to its roots some 5,000 years ago. This is because analysis of prehistoric air trapped inside bubbles inside Arctic ice planes reveals a proliferation of methane in the atmosphere at this time.

What are the organisms that convert organic waste to methane?

Thus the bioconversion of organic waste to methane generally needs the consortia of interacting microorganisms including fermentative bacteria, H 2 -producing acetogenic bacteria and methanogens, and the final generation of methane by methanogens is the rate-limiting step.

Where is straw biogas made?

The straw biogas plants have many technological difficulties due to the character of straw. In response to these problems, three kinds of anaerobic digesters are highly proposed, namely CSTR, membrane covered trough (MCT) and vertical plug flow anaerobic reactor (VPF) [114]. The Green Harbor straw biogas plant located in Chongming, Shanghai, China employs CSTR technique as well as biogas-heat-power-fertilizer cogeneration mode and annually generates electricity 584,000 kW [115]. Biogas plant applied MCT technique, like Daxing plant in Beijing, has a high energy efficiency [114]. Another plant with VPF reactor in Xinjin of Sichuan processes 1.3 t of straw each day and produces 400–600 m 3 biogas [116].

Where is methane produced?

Methane is produced by a group of anaerobic bacteria called methanogens in marshes, swamps and wetland soils — the largest natural source of the gas.

What are the sources of methane emissions?

A major source of methane emissions is the decomposition of fertilizers and crop residues in flooded rice cultivation. The most effective option to reduce these emissions would be to prevent submergence of rice fields and to cultivate upland rice or other upland crops.

How does methane get out of the atmosphere?

The main mechanism for removal of methane from the earth’s atmosphere is oxidation within the troposphere by the hydroxyl radical (OH). A hydroxyl radical is a negatively charged oxygen atom bonded to a hydrogen atom (OH).

What gases are in flatus?

Over 99% of the volume of flatus is composed of odorless gases. These include oxygen, nitrogen, carbon dioxide, hydrogen and methane. Not all humans produce flatus that contains methane.

What is the effect of landfills on the environment?

But at the landfill, the food and yard waste that trash contains is decomposing and releasing methane, a greenhouse gas that’ s 28 times more potent than carbon dioxide. Landfill gas also contributes to smog, worsening health problems like asthma.

What is the chemical formula for methane?

Methane (US:; UK: ) is a chemical compound with the chemical formula CH4 (one atom of carbon and four atoms of hydrogen). It is a group-14 hydride and the simplest alkane, and is the main constituent of natural gas.

How much methane does rice produce?

The statistic that rice produces 12% of anthropogenic methane and that the methane produced by rice farming makes put about half of crop -related greenhouse gas emissions come from a white paper prepared by the Environmental Defense Fund (EDF).

What are the main sources of methane emissions from agriculture?

The main sources of methane (CH 4) emissions from agriculture are enteric fermentation, manure management, rice cultivation and residue burning, with FAOSTAT being the main source of statistics on agricultural emissions [ 1 ].

Why is methane abatement important?

Methane abatement is clearly an important component of a land sector that helps to deliver a 1.5°C world, with interventions both on the supply side (reduction in emissions from enteric fermentation, rice and manure) and the demand side (dietary shifts toward plant-based diets and reduction in food loss and waste) necessary to achieve a land sector that is compliant with the Paris Climate Agreement [ 94 ], with the IPCC in the Special Report on 1.5°C target suggesting that agricultural methane emissions need to be 24–47% below 2010 emissions in 2050 [ 105 ].

How much of the food supply chain is lost or wasted?

An estimated 26% of food produced globally is lost or wasted each year, equivalent to 6% of global anthropogenic greenhouse gas emissions [ 88 ]. Methane-intensive foods, such as ruminant meat and dairy, play a disproportionately large role in these food wastage emissions and one that has continued to expand over the past half-century [ 84 ].

How does biogas affect the environment?

Biogas is a methane-rich gas mixture, generated from the anaerobic decomposition of organic matter that can be burnt to release energy . The use of organic wastes in the production of biogas has the potential to change net CH 4 emissions in two ways. Collection of organic wastes for use as a feedstock for biogas production may reduce CH 4 emissions by removing wastes from the environment where uncontrolled anaerobic decomposition can result in significant emissions of CH 4 [ 70 ]. However, emissions of CH 4 may also be increased by CH 4 leakage from the biogas digesters [ 70 ], piping [ 71] and appliances [ 72, 73 ]. The net effect on CH 4 emissions is a balance between these different processes. While we focus here only on the impact of biogas on CH 4 emissions, it should be noted that using organic wastes in biogas production has further impacts on total greenhouse gas emissions by potentially replacing fossil fuels [ 74 ], reducing deforestation associated with use of wood as a fuel [ 75, 76] and increasing soil carbon sequestration associated with the application of bioslurry as an organic fertilizer [ 77 ]. These latter impacts are not discussed further here.

How does agriculture affect the sink capacity of soils?

Cultivation of land for agriculture can significantly reduce the sink capacity of soils to oxidize CH 4 [ 14 ]. Mineral soils under forests and other natural vegetation act as the strongest CH 4 sink, followed by grasslands, with the sink strength weakest in cultivated soils and those receiving nitrogen fertilizer [ 7, 14, 15 ]; as such, as cropland has expanded, the CH 4 sink strength of soils globally will have declined [ 14 ]. When mineral soils become anaerobic, the net flux to the atmosphere can be positive, with waterlogged soils becoming a CH 4 source, often with large emission rates [ 16 ]. When soils are deliberately flooded, e.g. for paddy rice cultivation, they can become very large global sources of CH 4 as described in §1 a [ 7 ].

Is methane produced from animal waste?

Methane production from animal wastes is also an anaerobic microbial process and occurs mostly when animal wastes are stored (manure management). Smaller quantities are produced from wastes deposited directly onto the ground. Manure type (e.g. wet versus dry), storage method, storage duration, manure chemical composition and temperature all influence the quantity of manure produced per unit of substrate [ 8 ].

What are the best ways to reduce methanogenesis?

A wide range of specific agents and dietary additives have been tested, mostly aimed at suppressing methanogenesis. These include ionophores, which are antibiotics that can reduce CH 4 emissions [ 46 – 48 ], but their effect may be transitory [ 49] and they have been banned in some jurisdictions, such as the European Union. Halogenated compounds which inhibit methanogenic bacteria [ 50, 51] have also been tested, but their effects, too, are often transitory and they can have side effects such as reduced calorie intake. Probiotics, such as yeast culture, have shown only small, insignificant effects [ 48 ], but selecting strains specifically for CH 4 reducing ability could improve results [ 52 ]. Propionate precursors, such as fumarate or malate, reduce CH 4 formation by acting as alternative hydrogen acceptors [ 53 ], but are effective only at high doses and are, therefore, expensive [ 54 ]. Vaccines against methanogenic bacteria have been developed but are not yet commercially available [ 55 ]. Bovine somatotrophin (bST) and hormonal growth implants do not specifically suppress CH 4 formation, but by improving animal performance [ 56, 57] they can reduce the emission intensity (emissions per unit of product) of meat/dairy [ 58, 59 ], but like ionophores, are banned in some jurisdictions, such as the European Union. Some natural feed additives, such as seaweed, have been tried [ 60 ].

What is methane fermentation?

Methane fermentation is a versatile biotechnology capable of converting almost all types of polymeric materials to methane and carbon dioxide under anaerobic conditions. This is achieved as a result of the consecutive biochemical breakdown of polymers to methane and carbon dioxide in an environment in which a variety of microorganisms which include fermentative microbes (acidogens); hydrogen-producing, acetate-forming microbes (acetogens); and methane-producing microbes (methanogens) harmoniously grow and produce reduced end-products. Anaerobes play important roles in establishing a stable environment at various stages of methane fermentation.

How many strains of methanogens have been isolated?

However, as a result of a greatly improved methanogen isolation techniques developed by Hungate (6), more than 40 strains of pure methanogens have now been isolated. Methanogens can be divided into two groups: H 2 /CO 2 – and acetate-consumers. Although some of the H 2 /CO 2 -consumers are capable of utilizing formate, acetate is consumed by a limited number of strains, such as Methanosarcina spp. and Methanothrix spp. (now, Methanosaeta), which are incapable of using formate. Since a large quantity of acetate is produced in the natural environment (Fig. 4-1), Methanosarcina and Methanothrix play an important role in completion of anaerobic digestion and in accumulating H 2, which inhibits acetogens and methanogens. H 2 -consuming methanogens are also important in maintaining low levels of atmospheric H 2 .

Which kingdoms are methanogens?

On the basis of homologous sequence analysis of 16S rRNAs, methanogens have been classified into one of the three primary kingdoms of living organisms: the Archaea (Archaebacteria). The Archaea also include major groups of organisms such as thermophiles and halophiles. Although Archaea possess a prokaryotic cell structure and organization, they share common feature with eukaryotes: homologous sequences in rRNA and tRNA, the presence of inn-ones in their genomes, similar RNA polymerase subunit organization, immunological homologies, and translation systems.

How is acetate made?

Although some acetate (20%) and H 2 (4%) are directly produced by acidogenic fermentation of sugars, and amino acids, both products are primarily derived from the acetogenesis and dehydrogenation of higher volatile fatty acids (Fig. 4-1; Stage 2).

What are the main substrates available in the natural environment?

Methanogens are physiologically united as methane producers in anaerobic digestion (Fig. 4-1; Stage 3). Although acetate and H 2 /CO 2 are the main substrates available in the natural environment, formate, methanol, methylamines, and CO are also converted to CH 4 (Table 4-3).

How much more powerful is methane than CO2?

Whether from fossil fuels or agricultural practices, a kilogram (kg) of methane released today warms the earth 104 times more powerfully than a kg of CO2, when comparing over the first ten years. (130 times that of CO2 when accounting for feedback effects). 4

How much CH4 is in the dairy industry?

The dairy sector accounted for 1,729 kt CH4 from enteric emissions and 1,281 from manure emissions, totaling 3.01 million tons in 2019. (see tables 5-4 and 5-8 above from EPA Inventory of Greenhouse Gases). The dairy herd count grew from 8.801 million at the end of 2019 to 8.866 22 at the end of 2020. Therefore, a conservative estimate of emissions for 2020 can be 3 million tons.


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