Carbon Grazing reduces methane
There is a lot to be gained by moving the framework of the debate from just "carbon" offsets to also include "greenhouse" offsets i.e. methane. When comparing the components contributing to climate change, methane has 21 times the effect of carbon dioxide. It is hard work when you concentrate on carbon only which is a factor of 1 in the greenhouse calculation.
Methane emissions and feed digestibility
"There is a relationship between methane emissions and feed digestibility, therefore, modifying the feed intake for digestibility will reduce methane emissions" (Dr Roger Hegarty).
Linking methane emissions to profit
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.
How to respond
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 debate on reducing methane from ruminants needs to focus more on what is suitable pasture management.
Carbon Grazing is a "systems" approach and views methane as another outcome of carbon management. There are to two components when linking Carbon Grazing outcomes to reduced methane production. Firstly, the improved quality of the diet available to ruminant animals in average years and secondly, the reduced extent to which the diet deteriorates in dry times (i.e. the availability of "green pick" over time).
The "ongoing green pick" message is a more subtle one. This relates to plants remaining green for longer (ongoing higher digestibility) as well as being able to respond to small falls of rain in dry years (digestibility spikes). Again this is a 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 periods of time.
Finally, those with drought resistant plants like Old Man Saltbush and fodder trees have an ongoing supply of protein (green pick), and therefore produce the least amount of methane per kg of production in dry times.
It is important to realise that improving the feed quality will only lower methane emissions from ruminants if total production remains the same. 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.
Excluding agriculture from 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.
Methane emissions per kilogram
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 perenniality of pastures is the other contributing factor, over time, to reducing methane production. This is because perennial pastures are less affected by seasonal variability.
Conclusion
In Australia, grazing of rangelands is the most extensive 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. To quote Warwick Jones when he was Assistant Manager Greenhouse in DAFF, "Two things stand like stone; profitability and sustainability are the cornerstones of greenhouse emission reduction in grazing."
Methane, like so many other environmental issues and rural profit, is closely linked to carbon stocks in the landscape. Maintaining these carbon stocks relies on an appreciation that pasture rest is TIMING not TIME (i.e. the basis of the Carbon Grazing principle).
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