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Literature review of nonenteric methane emissions from red meat production
What the report is about
This report summarises a review of public domain literature regarding the emission of methane from feedlot manure, grazed soils, and pasture manure deposits. Emissions processes are examined, measured emissions summarised, and potential mitigations highlighted.
Who is the report targeted at?
This report is directed at informing Meat and Livestock Australia staff and industry representatives. The literature review is also conducted as an initial step in a experimental research program.
The range of Australian industries is set to encounter considerable pressure for decreased greenhouse gas emissions. While the effect of emissions regulation on red-meat production remains unclear, the lead time to develop the technologies required to make an impact on emissions necessitates that R&D should commence promptly. Even if the agricultural sector is exempted from a carbon pollution reduction scheme, carbon offset opportunities within the sector may be considerable and a potential means of decreasing the costs associated with the introduction of the carbon pollution trading scheme to other sectors.
In order to implement a program of research into greenhouse gas emissions it is necessary to have an accurate grasp of the current state of understanding, and the problems that face the red-meat production sector.
The objectives of this project were to conduct a comprehensive review of:
- The manure methane emissions processes and controlling factors likely to operate in Australian systems;
- Available data regarding grazing and feedlot enterprise manure methane emissions in published literature;
- Knowledge gaps with regard to the red-meat production sector;
- The opportunities to mitigate manure methane emissions in these production systems; and How published data compares with current inventory calculations techniques.
The carbon and nitrogen cycles are inextricably linked and nitrous oxide emission mitigation cannot be conducted without consideration of methane emissions.
Methane itself is both formed and consumed in manure management systems. Methane formation is favoured by warm (30 to 40°C), moist conditions combined with low oxygen supply, and a degradable organic material. The process also tends to proceed under near neutral conditions in terms of pH. Methane consumption in manure systems, is also favoured by warmer conditions. However, methane consumption requires oxygen and increases where pH is slightly above neutral, where ammonia concentration is low, and phosphorus and potassium are available.
Manure methane emissions from Australian grazing systems are likely to be relatively unimportant.
While data is incomplete, it is likealy that nitrous oxide emissions from feedlots (direct plus indirect) exceed methane emissions from their manure management system. International data tends to indicate that the major candidates for emission mitigation are the manure pad plus enteric source, stockpiles, and composting. However the available data is sparse and often inappropriate as a basis for Australian industry decisions.
Variables that contribute strongly to differences in manure methane production are temperature, moisture, diet of the animal, drying conditions, and manure handling. A range of feed-pad mitigations related to the above factors may prove effective and economical.
Composting studies include a range of practices that perform extremely poorly in terms of methane emissions. This is a surprising result considering that from current process understanding, composting should be a mitigation practice. Improved aeration, turning, carbon:nitrogen ratios, windrow covering, and moisture management practices may allow the emissions benefits of composting to be realised.
Inventory enteric emissions estimates for feedlots are within the range of values reported internationally for the sum of enteric and manure emissions from pens but are more than 50 % higher than the mean of published data. On the other hand, the international data on cumulative manure management losses reviewed in this paper tend to exceed those calculated using the Australian inventory method. Australian data from specific sources is still largely lacking.
The greatest weakness of the National Greenhouse Gas Inventory approach is the lack of ability to recognise emission decreases related to improved management.
Recommendations from the manure methane review
Realistic Australian methane emissions data is urgently required for manure on feedpads and compacted stockpiles.
There is a need to identify how methane emissions can be minimised from composting operations through managements that affect aeration, carbon:nitrogen ratio, changing moisture, manipulating free air space, and facilitating methane oxidation.
The magnitude of manure methane emissions at the feed pad is currently unknown. If the recommended methane emissions study reveals this as a substantial source, a range of mitigations are likely to be effective and may provide a good opportunity to decrease emissions — and should be investigated.
Improved emissions algorithms are required to allow a management-responsive inventory calculation approach to be developed (Tier III).
This page was last updated on 25/07/2017
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