It’s tempting to blame burping cows for methane emissions. But while nature cannot distinguish between naturally occurring methane and methane derived from fossil fuels and anthropological activity, humans can – and should. Methane has a role to play in sustainable farming. We cannot let the debate around methane emissions cloud the broader benefits of farming with ruminants, argues Stuart Meikle in part three of this series.
What is methane’s role in sustainable farming?
Methane is a highly potent greenhouse gas. That is an established fact. It is produced in Nature from a multitude of sources naturally, and especially from wetlands. The concern is the additional methane that is generated from human activities and when the methane emanates from fossil fuels. A significant focus is also on farming and especially ruminant agriculture where microbial fermentation converts forage and feed into products that can be digested and utilized by the animal. This methane can be swiftly reduced by farmed-ruminant herd reduction.
The key phrase above is utilized by the animal, whereas, de facto, the domesticated animal is being utilized by humankind and, thus, the methane produced by the animal is considered to be derived from anthropological activity. At its most simplistic, the human gains meat, milk, leather and various other products in exchange for placing a significant quantity of methane into the atmosphere. It is frequently considered to be a poor exchange.
The methane cycle within the carbon cycle
Prior to recent anthropological interference, methane sources would be balanced with methane sinks. Nature cycles methane. The methane cycle is considered to begin in the soil where methanogenic microorganisms break down organic matter in anaerobic condition. Such also occurs within landfills as methanogens break down the organic matter wastes, again in anaerobic conditions. In fact, methane is produced by methanogens wherever natural decomposition of organic matter occurs within anaerobic conditions. Some methane is consumed in the soil by methanotrophs, albeit this does not balance the production of methane by methanogens and the majority is emitted to the atmosphere. Nature then has the mechanisms to remove the methane from the atmosphere.
The primary mechanism for removal of methane from the atmosphere is oxidation within the troposphere by the hydroxyl radical followed by a long series of chemical reactions. The result is CO2 and H2O. Thus, methane is produced by organic matter degradation and later cleaned from the atmosphere by the hydroxyl radical over several years. Hence, the carbon from methane is then present in the atmosphere as CO2, a long-term, non-degradable greenhouse gas. Left at this stage, the CO2 would accumulate, but within Nature’s cycles it does not.
Methane also emanates from fossil fuel extraction. It is all CH4, and nature does not distinguish between the CH4 from fossil fuel derivation or that methane originating from organic matter degradation by methanogens. This anthropological-caused additional methane causes atmospheric methane rises and, ultimately, CO2 increases.
The methane cycle operates with the wider carbon cycle. It is not a discrete natural mechanism but a part of the ebbs and flows of Nature’s carbon cycle. The methane cycle may be considered to begin in the soil when it results from organic matter degradation, but it is produced by methanogens using organic material to generate energy to fuel their own activity. That carbon-containing organic matter may be of animal origin but, ultimately, it is itself still of plant origin. And as plants derive their carbon from atmospheric CO2, the carbon is fully cycled.
The addition of stored carbon (as in methane from fossil fuels) has exceeded the capabilities of the carbon cycle to maintain atmospheric CO2 levels and thus CO2 levels have risen. A widespread objective is now to remove this excess carbon from the atmosphere and sequester it in soils and long-life organic, usually, plant-based materials.
Where do ruminating animals fit in?
Ruminants are powered by the products created by methanogenic microbes consuming plant material. The by-product is CH4. If harnessed it is a supply of natural gas. If lost, it is a short-life, biodegradable greenhouse gas.
Were the plant material degraded naturally in aerobic conditions, it would still be converted to CO2 and its carbon returned to the atmosphere, albeit the carbon would be in a form readily available for reabsorption by growing plants. The speed of cycling means that this CO2 is not counted as a GHG, and unlike fossil-fuel derived carbon, it does not contribute to global warming. However, the residual plant material not decomposed aerobically, will first become CH4 before breaking down into CO2. This CH4 carbon may be retained within the soil, or it may be released into atmosphere, where it is eventually degraded into CO2 and H2O and becomes available for plant growth. It is important to remember that the carbon within CO2 is the primary nutrient utilized by growing plants.
The ratio of plant material degradation will differ with conditions. In wetlands, a high proportion of it happens in anaerobic conditions and, thus, major quantities of methane are released into the atmosphere. Carbon is also retained and over millennia becomes peat. Nonetheless, on balance peat degradation in the presence of oxygen (when drained and/or harvested) is a greater GHG problem than the methane emitted by the wetlands. In such a situation, CH4 emissions are considered acceptable, even though that methane creates no utilizable products, bar the utility attributable to the restoration of wetlands biodiversity and the high cultural value of boglands.
To summarize, peatlands lose a lot of soil carbon through oxidization. The drainage of wetland is a wilful human act and the carbon lost is counted as a GHG emission. Soil carbon loss from all cultivated land and some poorly managed pastures is a major issue across all soils but can be very evident on peat soils such as the Fens in East Anglia. Rewetting peatlands will halt the anthropological soil carbon loss, but it will be replaced with methane emissions. Are they anthropological, or is it accepted that they are natural? And is the slow, natural accumulation of peat then an offset? At what point is using natural methane-emitting systems acceptable to build soil carbon?
Similarly, is the methane from grazing herbivores the biodegradable cost of broadacre soil carbon accumulation?
The point is that the carbon that enters the atmosphere from organic matter decomposition, be it aerobically or anaerobically. All originated from growing plants that utilized atmospheric CO2 and solar energy, albeit other life forms may be an intermediary. Outside agriculture, Nature balances the CO2 absorption by growing plants with CO2 and CH4 emissions, albeit there is a slow accumulation (possibly with a soil percentage and/or soil volume saturation point) of carbon retained in the soil. Henceforth, the crux, from an agricultural viewpoint, should be to avoid using fossil-fuel-emanating carbon when growing plants and practices which inhibit soil carbon building.
The methane time-lag problem
Over the last 15 years there has been a great deal of focus placed upon the methane emanating from ruminant-based agriculture. That CH4 has a global warming potential 28x that of CO2 is a well-known fact. Sadly, fewer are aware of the complex of issues around nitrogen, be it nitrates pollution in water, ammonia in the air or nitrous oxide emissions (c. 300x more potent than CO2 and 10x more so than CH4). N2O is also exceedingly long lived. In contrast, CH4 is short-lived, and biodegradable, and its carbon was initially drawn from the atmosphere by plants.
The methane cycle operating within the wider carbon cycle is natural, period. The concern is when further CH4 is attributable to human act. Thus, constant farmed ruminant numbers do not add extra CH4 and over a period of a few years the CH4 is broken down to CO2 and H2O, with the CO2 replacing the CO2 originally absorbed by the growing plant. That is how Nature evolved the system. Extra ruminants will increase CH4 for the duration of the time it takes the carbon cycle to return the CH4 to plant usable CO2. The ‘extra’ is not now deemed acceptable and a fall in ruminants to target swift CH4 reduction is seen as an expedient short-term carbon removal option.
There is, nonetheless, a great nuance shortfall in the above. The ruminant herd should also be considered in the light of fossil fuel usage and the emissions and pollution from nitrogen use. It could be argued that the complex of issues around nitrogen are more long-term and damaging than those surrounding biodegradable CH4 creation.
Artificially feeding farmed ruminants
Should the aim be to mimic natural systems as far as possible when utilizing ruminants within agriculture? As will be explained later, the ruminant provides many essential food system services and should be viewed as a strategic asset, not as a polluter of our planet. In this context, scrutiny needs to be placed upon where the plant material fed to the ruminant is linked to fossil-fuel use and artificial nitrogen use (which itself relies on fossil fuel) and, to a slightly lesser degree, the use of other artificial plant nutrient forms. These all pollute and emit. The excess focus on agricultural CH4 has diverted the debate away from these important farming-system issues.
The evaluation of ruminants within agriculture should be based upon the full complex of products and services that they can deliver (to follow). It should also be based upon differentiating the natural from the unnatural in how they are farmed. As with methane emanating from wetlands, with ruminants, the nuance is to distinguish the anthropological acts within the system from the natural ones. Ruminant CH4 reduction should be focused upon eliminating the anthropological CH4 sources while retaining the broader benefits of farming with the ruminant.
In so doing we will build sustainable food systems and not, unwittingly, undermine them via misunderstanding.
Hence, the emphasis should be on where artificial fertilizers are used to stimulate grass and forage production. The extra organic matter may be grown using fossil-fuel based stimulants, albeit it is increasingly evident that farming systems that work with nature can still be highly productive of herbage. And they will need to be given the size of the human population. Thus, the focus of ruminant farming must be on utilizing the crops that can feed themselves from the atmosphere and the soil profile. On arable land that will be extended to building soil fertility to feed later crops that the soil biome cannot feed without fertility-building assistance. It should also be self-evident that the ruminant should not consume feeds directly emanating from this latter group of crops.
There is a school of thought that simplifies addressing climate change to removing ruminant agriculture. That is invariably based on over-simplified assessments, and it certainly does not include all the products and services involved. Possibly, the most important will be soil-restoration-driven ecosystem-restoration. These are activities where the ruminant has strategic value. The quid pro quo is then to seek short-term climate-change mitigation by reducing ruminant numbers where they are reliant on fossil fuels and especially where the consumed plant material is linked to artificial stimulation and/or feeding human-edible crops that also rely on such stimulation.
Biogenic methane or fossil fuels
For some, it will be a difficult concept, but sustainable food systems will mean substituting fossil fuel usage with biodegradable methane, albeit the use of the latter will have to be very carefully considered. Without methane or, specifically, the energy created by methanogenic microorganisms when breaking down plant material, it will not be possible to achieve broadacre soil restoration and soil fertility building. Without such, we will not be able to sustainably grow food, fibres or biofuels. With fossil fuels and biogenic methane, it is a case of ‘either/or’.
Further, the methane emanating from the microorganisms breaking down plant material can be harnessed itself as an energy source if captured. Liquified it can provide a mobile energy source to power agricultural operations.
Methane is recognized as a bioenergy source and manures are seen as a feedstock for bioenergy creation. Direct from the ruminant methane is not, which is reasonable given the complexities involved. The grazing ruminant should also be living in a near-to-natural environment (and thus far less reliant on fossil fuels). The question that should arise with methane as a biofuel is whether the feedstock itself is reliant on fossil-fuel linked artificial plant nutrition. If it is, its sustainability credentials are poor. Across the board it will come down to the constraints on plant nutrition and the capacity of restored, carbon- and humus-rich, functional soils to provide that nutrition.
In the final installment of this series, Stuart Meikle will outline solutions for fossil-fuel-free farming.