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Dietary manipulation of animal diets by reducing crude protein (CP) intake is a strategic NH 3 abatement option as it reduces the overall nitrogen input at the very beginning of the manure management chain. This study presents a comprehensive metaanalysis of scientific literature on NH 3 reductions following a reduction of CP in cattle and pig diets. Results indicate higher mean NH 3 reductions of 17 ± 6% per %-point CP reduction for cattle as compared to 11 ± 6% for pigs. Variability in NH 3 emission reduction estimates reported for different manure management stages and pig categories did not indicate a significant influence. Statistically significant relationships exist between CP reduction, NH 3 emissions and total ammoniacal nitrogen content in manure for both pigs and cattle, with cattle revealing higher NH 3 reductions and a clearer trend in relationships. This is attributed to the greater attention given to feed optimization in pigs relative to cattle and also due to the specific physiology of ruminants to efficiently recycle nitrogen in situations of low protein intake. The higher NH 3 reductions in cattle highlights the opportunity to extend concepts of feed optimization from pigs and poultry to cattle production systems to further reduce NH 3 emissions from livestock manure. The results presented help to accurately quantify the effects of NH 3 abatement following reduced CP levels in animal diets distinguishing between animal types and other physiological factors. This is useful in the development of emission factors associated with reduced CP as an NH 3 abatement option.

Farm livestock manure is an important source of ammonia and greenhouse gases. Concerns over the environmental impact of emissions from manure management have resulted in research efforts focusing on emission abatement. However, questions regarding the successful abatement of manure-related emissions remain. This study uses a meta-analytical approach comprising 89 peer-reviewed studies to quantify emission reduction potentials of abatement options for liquid manure management chains from cattle and pigs. Analyses of emission reductions highlight the importance of accounting for interactions between emissions. Only three out of the eight abatement options considered (frequent removal of manure, anaerobic digesters, and manure acidification) reduced ammonia (3-60%), nitrous oxide (21-55%), and methane (29-74%) emissions simultaneously, whereas in all other cases, tradeoffs were identified. The results demonstrate that a shift from single-stage emission abatement options towards a wholechain perspective is vital in reducing overall emissions along the manure management chain. The study also identifies some key elements like proper clustering, reporting of influencing factors, and explicitly describing assumptions associated with abatement options that can reduce variability in emission reduction estimates. Prioritization of abatement options according to their functioning can help to determine low-risk emission reduction options, specifically options that alter manure characteristics (e.g., reduced protein diets, anaerobic digestion, or slurry acidification). These insights supported by comprehensive emission measurement studies can help improve the effectiveness of emission abatement and harmonize strategies aimed at reducing air pollution and climate change simultaneously. Greenhouse Gas and Ammonia Emissions from Different Stages of Liquid Manure Management Chains: Abatement Options and Emission InteractionsErangu Purath Mohankumar Sajeev,* Wilfried Winiwarter, and Barbara Amon L ivestock production and rearing is a major source of ammonia (NH 3 ) and greenhouse gas (GHG) emissions. In 2014, the livestock sector contributed a share of 53% methane (CH 4 ), 21% nitrous oxide (N 2 O), and 75% NH 3 to total agricultural emissions in the European Union (EU-28) (UNECE, 2016;UNFCCC, 2016). The negative impacts of these emissions on the environment have been widely reported. Accumulation of GHGs in the atmosphere causes climate change, which leads to undesirable consequences like sea level rise, increase in extreme weather events, and losses in food production (Stocker et al., 2013). Ammonia, on the other hand, poses a threat to terrestrial and aquatic systems and contributes to the formation of particulate matter in the atmosphere, which is harmful for human health . Ammonia volatilization and subsequent atmospheric deposition is also a source of indirect N 2 O emissions (De Klein et al., 2006). Given the projected increase in demand for livestock products (Steinfeld et al., 2007), there is a pressing need to ab...

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