Methane discussion paper
(19th September 2007)
There is a need to broaden the carbon debate from just "carbon offsets", which has concentrated on trees, to also include "greenhouse offsets" including reducing methane emissions. Understanding how ruminant animals produce methane explains the link between methane emissions and feed digestibility. The best strategy for reducing methane emissions is to promote that methane emissions are positively linked to profit.
In discussing how to respond, the current soil carbon debate needs to be linked to the methane debate.
Differences between various production systems become clearer when the outputs are expressed as the amount of methane emitted per kg of production. While longer more complex alternatives for methane reduction are being considered, the conclusion on how best to respond in the short term should focus on improvements to pasture management.
REDUCING METHANE EMISSIONS
The 2003 National Greenhouse Gas Inventory, stated that livestock contributed the largest share of agricultural greenhouse gas emissions, accounting for 12 % of the net national total. 80% of agriculture's emissions are generated by the digestive processes of ruminant animals. This process, enteric fermentation produces methane.
The realisation that it is going to take time and investment to develop new technologies to reduce the emissions of fossil fuels, has seen a scramble towards offsets as a short term solution. The outcome of reducing methane production compared with more popular greenhouse approaches such as planting trees (as an offset), needs to be given greater consideration. Reducing methane emissions now immediately reduces greenhouse emissions whereas trees are a steady offset over time.
Furthermore, only a small percentage of Australia is suitable for forestry while millions of hectares are used for grazing. If a tree dies the offset fails, while methane reduction is permanent.
There are significant gains available by broadening the debate from "carbon offsets" only to include "greenhouse offsets" i.e. methane. When comparing the components contributing to climate change, methane has 21 times the effect of carbon dioxide. So why concentrate on carbon alone, which is a factor of only 1.
HOW RUMINANT ANIMALS PRODUCE METHANE
The rumen, or first stomach, is a very complex internal ecosystem containing millions of micro-organisms in a complex relationship with each other. Fermentation of plant material by these organisms allows ruminants to convert lower quality feed to energy more efficiently than monogastrics like humans, birds and pigs.
Ruminants animals (sheep, cattle and goats) produce a lot of hydrogen during digestion, which is removed by organisms called methanogens. They do this by combining the hydrogen with carbon dioxide to produce water and methane. Methane then passes out of the animal in burps as it chews its cud.
It has been known for many years that methane production represents poor conversion of food to energy and, as such, is a waste gas. If it could be reduced, then the productivity of the animal would be much improved. Because the rumen is so complex, this has proved to be easier said than done. Many methods have failed because no effective way has yet been found to carry away the hydrogen from the rumen.
METHANE EMISSIONS AND FEED DIGESTIBILITY
DAFF minister Peter McGauran recently highlighted why we are struggling with the methane debate when he said "we are yet to come to grips with the variability of emissions that exists at the farm scale, due to the significant impact diet has on an animal's production of methane."
"There is a relationship between methane emissions and feed digestibility, therefore, modifying the feed intake for digestibility will reduce methane emissions" (Dr Roger Hegarty, NSW DPI).
Put another way, if you increase the efficiency with which an animal digests its feed, you reduce the amount of energy released by the rumen micro-organisms. This energy is in the form of methane gas, which should be channelled into growth rather than into the atmosphere.
The methane debate is one of subtleties with the true issue being the production of methane per kg of production. The major strategy for reducing methane production will be the same as the key driver for profitability in grazing: reducing the number of grazing days per kilo of product.
Putting the methane issue into commercial perspective, it has been suggested that a 1% increase in production through a superior diet results in a 1% reduction in methane. The difference in methane production between grazing systems can be substantial. The level of methane production is another example of the general principle that the greenhouse outcomes of rural production reflect financial efficiency. Production of the greenhouse gas, nitrous oxide (310 times the effect of carbon dioxide), is also a reflection of commercial efficiency.
The soil carbon debate needs to be linked to the methane debate. This is because all else being equal, a landscape with higher soil carbon levels will supply plants of higher digestibility and hence lower methane production per kg of production. Responsible managers contribute less to methane production simply because they have higher quality pastures. The carbon: nitrogen ratio of their pastures is superior. The management required to maintain higher soil carbon levels will also see the survival of the most digestible plants. Furthermore, this same management ensures the most digestible plants bulk up more in response to rainfall. The debate on reducing methane from ruminants needs to focus more on what is suitable pasture management.
The "ongoing green pick" message is a more subtle one. This relates to plants remaining green for longer (ongoing higher digestibility) and being able to respond to small falls of rain in dry years. Again this is a soil carbon issue, as soil carbon levels influence water infiltration and water holding capacity of the soil. Combined, these two processes promote plant growth and the availability of green pick for longer as the season deteriorates. Returning to pasture management, plants managed correctly have more extensive root systems and retain higher energy reserves necessary for responding to rain. Those with more "sustainable" pastures due to healthier plants and healthier soil, supply their ruminant animals "green pick" for longer going into drought and so produce a lot less methane in dry times.
Finally, those with drought resistant plants like Old Man Saltbush and fodder trees have ongoing protein (green pick), so produce the least amount of methane per kg of production in dry times. Given all these variables, if Government ever decides to levy a carbon tax on methane production, one size will not fit all. Apart from the digestibility of feed, the amount of methane emitted is related to other factors such as the weight of the animal.
It is important to realise that improving the feed quality will only lower methane emissions from ruminants if total production remains the same. Sheep and cattle will generally eat as much as their rumen will hold. Feed with higher digestibility will pass through the rumen more quickly allowing the animal to eat more. This way an improved pasture may actually increase an animal's food consumption and thus more methane will be produced "on a daily basis". Where the true methane and commercial gains are to be made, is that better quality feed can significantly reduce the number of grazing days required for producing a kilo of wool or meat.
Those who want to shift the emphasis of the greenhouse debate from soil carbon sequestration to methane reduction, suggest that reducing methane by 10% would equal the best possible soil management for carbon sequestration. While this is probably true and highlights that methane reduction will account for the largest positive contribution agriculture can make to greenhouse reductiion, it further reinforces the importance of introducing more carbon into the soil. Given the dual outcomes of carbon sequestration and offsetting emissions, this makes it the most cost effective way for agriculture to reduce its greenhouse footprint. Another commercial positive is that the change in pasture management required is more reliant on information flow than capital expenditure.
Agriculture Minister, Peter McGauran supports the need to focus on ways to help farmers lower their greenhouse emissions and learn about what is needed for participation in emissions trading. Modelling of the above issues will be necessary if the livestock section of rural industries is to be supplied with a cost effective method of being involved in the carbon trading market. The legal aspects of trading will require transparency and quantification to support contracts entered into.
Responsibility for methane outcomes and soil carbon balances may be treated differently in a technical sense. When discussing soil carbon balances, it is important to appreciate that there is a climate signal and a management signal. In the case of soil carbon balances, producers are not responsible for climate impacts, but they are responsible for management impacts. In the case of methane they may be seen as responsible for climate impacts i.e. they may be seen as in control of the outcomes.
Currently in dry times, producers make the commercial decision on whether the animals are retained on pastures or removed. This decision is influenced by their ability to maintain efficient digestion by animals. Placing a value or cap on methane production will add a further commercial consideration to their current decision making process related to digestive efficiency. Apart from the case of maintaining future breeding stock, it is always in a producer's commercial interest to do what happens to be in the best interest of the rest of society. This is because the greenhouse outcomes of rural production reflect financial efficiency.
Not including agriculture in the carbon trading market will lock industry out of a major opportunity to offset their emissions. If the market is limited to trees, then the market will be smaller and industry will have to pay more for offsets. This increase in cost will flow on to consumers and business in general with higher electricity costs as an example. To compliment the outcome of industry receiving lower priced offsets for their emissions, trades will transfer funds to rural industries. Because the funds will be directed into changed land management, this will enable an improvement in Australia's natural resource base. Apart from all the positive environmental outcomes, there will be a lessening of the impact of climate change on agriculture due to a more resilient landscape. Furthermore, there will be the potential for increased export income from fewer animals.
There has been fear in some agricultural circles regarding the whole greenhouse debate and how it is going to impact on conventional management practices. The people who are positive are the ones who see the opportunities that regenerative management practices provide. These people seek the completion of science and modelling to allow the representation of the positive outcomes as well as financial reward.
ALTERNATIVES FOR METHANE REDUCTION
It is currently understood that some animals produce less methane than others on the same diet. Following this path to reduce methane will take time as first the markers to identify them will have to be identified. Then their numbers will take time to breed up.
Rumen modification has and is currently being researched and does hold potential. There are publications available from CSIRO, the Department of Climate Change (formally the Australian Greenhouse Office) and the sheep industry covering various aspects of rumen modification research and opportunities.
While rumen modification options are essential, in the short term the best solution is simply focusing on the diet. It has been suggested that in some areas, methane emissions could be reduced by 50% to 60% by simply modifying grazing management decisions.
METHANE EMISSION PER KILOGRAM OF PRODUCTION
Differences between production systems become clearer when the outputs are expressed as the amount of methane emitted per kilogram of production. This is determined by the speed of passage of food through the rumen. The faster the passage, the less methane produced per kg of production.
The speed of passage is determined by the carbon: nitrogen (C:N) ratio of the diet. The C:N ratio determines the health of the rumen and hence the level of production of methane. The C:N ratio determines the digestibility of the feed.
Cellulose in the walls of plants has to be broken down to get access to what is required. This occurs through fermentation in the rumen and is responsible for methane production. High roughage feed (high C:N ratio) ferments for longer and is not an energy efficient process. The longer the time of passage of the diet, the higher the production of methane. High quality feeds (balanced C:N ratio) flow through faster. The extreme case is the short pick at the end of drought which is too high in nitrogen in relation to carbon and flows too quickly. This is a case of the C:N ratio being wrong at the other extreme and animals performing poorly as they chase the short fresh growth.
The increased weight gains with higher quality diets result in animals going to slaughter sooner (termination of methane production). Lower quality diets see animals producing methane for a longer period of time to achieve the same level of production. The extreme of this is drought conditions when methane production is very high in relation to production.
The GRASSGRO modelling simulations include drought as part of showing the very close relationship between increased profitability in grazing systems and the reduction of methane emissions. With the simulation at the Wongan Hills site in Western Australia, the sheep at the highest stocking rate were kept in a Score 1 condition and gained only half a kilogram for a year. This, of course, closely approximates drought conditions. In this situation the sheep are emitting nine times more methane per kilo of live weight gain than they would be in the better conditions simulated at the lower stocking rate.
The GRASSGRO simulation has quite major implications for grazing management and greenhouse. It indicates that the pivot point for grazing systems that reduce greenhouse gas emissions is the management of "seasonal variability". In other words unless the digestibility of the feed can be maintained above about 50%, then emissions will skyrocket.
The perenniality of pastures is a contributor over time to reducing methane production. Perennials are less affected by seasonal variability. Complete annual pastures as a production base are not suited to the variable climate of Australia. Furthermore, they will struggle even more with the prediction of increased variability that climate change is predicted to bring. That said, annual plants are responsible for high production and lower methane in average seasons when they are a component of the pastures. In the areas where both C3 and C4 perennial grasses exist, pasture management to maintain the C3 component will be important. These C3 grasses have a higher digestibility and are responsible for lower methane emissions per kg of production.
Expanding the perennial debate past grasses, the importance of perennial saltbushes and fodder trees in the methane debate relates to their drought resistance. They are an ongoing source of protein (nitrogen) and are responsible for reducing "the C:N ratio of the total diet of animals in dry times". As an ongoing source of protein, they are responsible for maintaining a more balanced rumen, and hence lower methane emissions.
The drought resistance of Old Man Saltbush is also indirectly responsible for reducing methane production. At the end of dry times, OMSB can be used as somewhere to place animals to allow their removal from pastures with the arrival of rain. This resting at a critical time contributes to the health of perennial plants and the soil, which is the cornerstone of reducing methane. Put another way, it is resilient production systems that produce the least methane. Pasture rest at the right time is similar to reducing stock numbers in that it increases the quality of the diet available to animals.
In Australia, the grazing of rangelands is the predominant land use. Changes in management of these areas will have a significant impact on our country's greenhouse balance.
The greenhouse outcomes of rural production reflect financial efficiency.
Warwick Jones ex-Assistant Manager Greenhouse in DAFF is quoted as saying, "Two things stand like stone; profitability and sustainability are the cornerstones of greenhouse emission reduction in grazing."