Intermittent agitation of liquid manure: effects on methane, microbial activity, and temperature in a farm-scale study

Liquid manure storages are a significant source of methane (CH 4 ) emissions. Farmers commonly agitate (stir) liquid manure prior to field application to homogenize nutrients and solids. During agitation, manure undergoes mechanical stress and is exposed to the air, disrupting anaerobic conditions....

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Bibliographic Details
Published in:	Journal of the Air & Waste Management Association (1995) 2019-09, Vol.69 (9), p.1096-1106
Main Authors:	VanderZaag, Andrew C., Baldé, Hambaliou, Habtewold, Jemaneh, Le Riche, Etienne L., Burtt, Stephen, Dunfield, Kari, Gordon, Robert J., Jenson, Earl, Desjardins, Ray L.
Format:	Article
Language:	eng
Subjects:	Agitation Agricultural equipment Agricultural resources Agricultural technology Air temperature Anaerobic conditions Animal wastes Archaea Biological activity Disruption Emission analysis Emissions Farms Liquid manure Manure Manures Methane Methanogenic bacteria Microbial activity Microorganisms Mitigation Nutrients Summer Temperature Temperature effects
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Summary:	Liquid manure storages are a significant source of methane (CH 4 ) emissions. Farmers commonly agitate (stir) liquid manure prior to field application to homogenize nutrients and solids. During agitation, manure undergoes mechanical stress and is exposed to the air, disrupting anaerobic conditions. This on-farm study aimed to better understand the effects of agitation on CH 4 emissions, and explore the potential for intentional agitation (three times) to disrupt the exponential increase of CH 4 emissions in spring and summer. Results showed that agitation substantially increased manure temperature in the study year compared to the previous year, particularly at upper- and mid-depths of the stored manure. The temporal pattern of CH 4 emissions was altered by reduced emissions over the subsequent week, followed by an increase during the second week. Microbial analysis indicated that the activity of archaea and methanogens increased after each agitation event, but there was little change in the populations of methanogens, archaea, and bacteria. Overall, CH 4 emissions were higher than any of the previous three years, likely due to warmer manure temperatures that were higher than the previous years (despite similar air temperatures). Therefore, intermittent manure agitation with the frequency, duration, and intensity used in this study is not recommended as a CH 4 emission mitigation practice. Implications: The potential to mitigate methane emissions from liquid manure storages by strategically timed agitation was evaluated in a detailed farm-scale study. Agitation was conducted with readily-available farm equipment, and targeted at the early summer to disrupt methanogenic communities when CH 4 emissions increase exponentially. Methane emissions were reduced for about one week after agitation. However, agitation led to increased manure temperature, and was associated with increased activity of methanogens. Overall, agitation was associated with similar or higher methane emissions. Therefore, agitation is not recommended as a mitigation strategy.
ISSN:	1096-2247 2162-2906