Revision of key National Greenhouse Gas Inventory methods for Australian feedlots

Summary

The National Inventory Report (NIR) method for Green house gas emissions from feedlot cattle was updated in 2015. The revisions recognised a substantial reduction in emissions from the feedlot industry. However, recent research findings indicate the current emission factor for nitrous oxide (N2O) emissions from feed pads over estimates the sector’s emissions.

Consulting with the Department of Industry, Science, Energy and Resources (DISER) National Inventory Team and peer reviewed by Dr Matt Redding (QLD DAFF) and Prof. Deli Chen (UOM) and feedlot industry representative, this review has developed the evidence base for recommending a change in the emission factors for nitrous oxide from feedlot manure pads, suitable for submitting to the Inventory Team.

Objectives

• Develop the evidence base for recommending a change in the emission factors for nitrous oxide from feedlot manure pads via a targeted review, suitable for submitting to the National Greenhouse Gas Inventory Team.
• Present this evidence to the National Greenhouse gas inventory team and assist implementation if accepted.
• If required, provide new activity data to enable the National Inventory to calculate emissions for the feedlot industry.

Key findings

• This review of feedlot feed pad (drylot) nitrous oxide emission research has determined that the current emission factor is not supported by Australian research.
• The current emission factor, reported in the NIR, for direct N2O emissions from the feedlot pen (“dry lot”) is 0.02 kg N2O - N kg N excreted. On average, Australian studies report 73% lower emissions than the current Intergovernmental Panel on Climate Change inventory estimates.
• Here we propose that the emission factor for feed pads should be revised to 0.0054 kg N2O – N per kg of N excreted.

Benefits to industry

The alternative methods identified as part of this project may be a more accurate way detecting emission levels. This will result in recognition of a lower greenhouse gas footprint of the feedlot industry. The feedlot industry will see benefit because they will be able to accurately determine baseline emission levels.

MLA action

• MLA assisted Integrity Ag with presenting this evidence to the Australian Government national greenhouse gas inventory team.
• MLA supports evidence based research that may lead to revision of emissions from the sector if accepted by the Australian government.

Future research

• The national inventory currently relies on a factor that is derived from total excreted Nitrogen (N). Both Australian and International researchers have shown that this N-mass approach is not strongly supported by the studies examining the factors driving emissions from the feed pen, because N is not limiting in this environment. Further research from American feedlot studies have proposed prediction equations based on temperature and rainfall. No studies have provided an alternate model to explain this relationship for Australian conditions.
• Considering this lack of strong evidence of the association between N excretion rates and nitrous oxide, we consider it necessary to also recommend some explanatory text for the National Greenhouse Gas Inventory, to help direct future research and mitigation.
• Manure nitrogen is not the first limiting factor driving nitrous oxide emissions from the feed pad. Consequently, reducing manure N is less likely to influence emissions than would be suggested by the emission factor. Future research to provide a prediction method based on key drivers; temperature, rainfall and manure moisture (may lead to better process knowledge and a revised emission factor or prediction method in the future.

Related MLA projects

• B.FLT.0356 Final Report - Greenhouse gas emissions from intensive beef manure management
• B.CCH.1020 Manure management to reduce greenhouse emissions from cattle feedlots
• B.FLT.0148 Final Report - Abatement of nitrogen-based greenhouse gas emissions from beef feedlots
• FLOT.331 Final Report - Greenhouse gas emissions from Australian beef cattle feedlots