Greenhouse Gas Mitigation Strategies through Dairy Forage and Manure Management
Photo by C.A. Campbell
The United States Dairy Industry voluntarily chose to pursue a cut in greenhouse gas emissions from milk by 20% by the year 2020. As a part of that goal, scientists across the Midwest are working with dairy farmers to improve manure processing and cropping management practices, including land applications of dairy manure from farms, manure storage options, and manure processing. As soil and dairy researchers at the University of Wisconsin, we have been asked to consider mitigation opportunities involved in the manure management continuum, comparing management opportunities to reduce emissions associated with manure storage, processing, and land application to dairy forages. Additionally, we are interested in understanding some of the environmental trade-offs associated with these management practices, especially related to their influence on contaminating groundwater and nearby water bodies with nitrate. Through an extensive literature review, we concluded that manure is most versatile for greenhouse gas mitigation when it is separated into solid and liquid (slurry) manure pools. Solid manure pools can be covered or sealed to capture emissions in piles or with anaerobic digesters and liquid (slurry) manure pools are best mitigated when they are acidified, covered, or routinely emptied from storage. Manure management practices are currently regulated based on total manure phosphorus loads, and in order to shift to greenhouse gas mitigation strategies, industry support--through policies and subsidies--will be necessary to maximize farmer participation in greenhouse gas mitigation.
Research ObjectivesTo understand the mitigation potential and environmental impact of various manure management practices on dairy farms, we have three objectives.
- Determine greenhouse gas emissions from baseline practice, namely, raw (unprocessed) manure, and manure broadcast applications.
- Determine greenhouse gas emissions from mitigation strategies and evaluate these practices for differences.
- Synthesis the best management practices for mitigating emissions throughout the mitigation process.
Introduction to Greenhouse Gases in Dairy Systems
Unlike other industries, the dairy industry is a key producer of the greenhouse gases methane (CH4) and nitrous oxide (N2O). These emissions have 26 and 298 times the global warming potential of carbon dioxide respectively, which means these gases have a longer lifespan in the atmosphere and higher radiative forcing compared to emissions from other industries. With this in mind, the dairy industry is not only interested in mitigating all emissions, but also, when possible, changing emissions into less potent greenhouse gases, such as combusting methane gas to release carbon dioxide.
Sources of Emissions
Dairy related emissions (Table 1.0), are predominately related to manure management in dairy systems. Manure produces all three major greenhouse gases, carbon dioxide, methane, and nitrous oxide, while it is collected, processed, stored, and land applied as a fertilizer. Because the primary emissions from manure are methane and nitrous oxide, which have 26 and 298 times higher global warming potential than carbon dioxide, managing these systems to reduce emissions is an important step towards a more sustainable system. Chadwick et al.2011, suggests that manure management - among the phases outlined in this paper - are strongly interrelated based on the possible pathways of manure management.
In essence, the manure management continuum suggests that each phase of the manure management process allows for chemical and physical alterations to manure, which can significantly change the bi-products of the manure, including greenhouse gas emissions. For example, manure slurry, collected without bedding materials, is predominantly liquid and thus, is stored anaerobically, which results in very high methane emissions. When a slurry is land applied, the manure has a lower C:N ratio because the N has been preserved in storage--resulting in higher nitrous oxide emissions from land application. Comparatively, manure that is stored solid allows more oxygen into the manure pile, and therefore, there will likely be higher nitrous oxide emissions from this storage option. The primary goal of this study is to review how varying mitigation options in manure management can be combined to synthesize the best possible pathway to reduce emissions.
Table 1.0. Primary emission sources in dairy production systems in kg of CO2 equivalents of Energy Corrected Milk.
|Source of Emission||Methane Emissions||Nitrous Oxide Emissions|
| Enteric Fermentation
| Land Application
1Estimates from O'Brien et al 2014.
2Estimates from Aguirre et al. 2014.
Source: Chadwick et al. 2011
|Figure 3.0. Manure handling and management synthesis, with all management pools considered for this study. Commonly, manure is managed through two distinct pathways: manure solids and manure slurry. Within these management pools, there are further options for manure handling to mitigate greenhouse gas emissions. Figure: C.A. Campbell|
|Figure 4.0. Manure processing emissions as compared to reference, common manure practices. For manure solid (left), the best greenhouse gas mitigation strategy was to change the cows' diet, and manure processing practices, including compaction, and incorporation resulted increased emissions. For slurry manure (right), the more processing strategies were able to reduce emissions, including separation strategies (sep 1 = gravitational separation, sep 2 = screw press separation). When manure is separated, mitigation options become more versatile to dairy producers. Source: Hou et al. 2015|
|Processing Strategy||Cost of System, $||Mitigation Potential, % Reduced|
|Raw Manure (baseline)||$10,000-$15,000||0|
||(Cost of Labor)||-30 to -50 (produces more emissions than baseline)|
1System costs as reported by Lund et al. 2000.
2Reported by Beddoes et al. 2007.
3All emissions reported in kg CO2 equivalents
4Percent reduced compared to baseline, raw manure, in terms of CO2 equivalents of total greenhouse gas emissions produced by the system as reported by Hou et al. 2015.
After manure undergoes a treatment process it must be stored before the timing is right for the manure to be applied to cropland as a source of fertilizer or utilized as a source of animal bedding. Generally, a farmer's end use of the manure (fertilizer or bedding) is a large factor in deciding how the manure will be stored. For example, slurry (liquid) manure would not be used as bedding and therefore is stored in a slurrystore or lagoon, but solid manure that will be used as a source of animal bedding would not be stored in a slurrystore or lagoon but rather piled to increase the drying of the bedding. In order to mitigate greenhouse gas emissions when storing manure, solids must be managed to mitigate methane emissions and liquid slurry must be managed to mitigate nitrous oxide emissions.
Also, in today's dairy industry there are numerous regulations in place to protect the environment from pollution and degradation as a result of misplaced or leachate manure. With the scope of our research being modern commercial dairy farms, it is important to remember the standard that these farms are being held to in regards to environmental protection and that these regulations and standards are currently not an industry standard across all farm sizes.
Solid manure, which is generally either used as a source of fertilizer high in organic matter or as a source of animal bedding, is generally stored via the strategy of solids piling/stacking/stockpiling. As mentioned above, solid manure must be managed to reduce methane emissions. Our recommended methane mitigation strategies include preventing anaerobic conditions, reducing storage time, limiting the moisture content of the manure, maintaining storage temperature, increasing manure acidification, composting, and covering the manure (Montes et al., 2014).
Manure Land Application
No matter the timing of manure spreading or land application strategy, the primary greenhouse gas of concern manure land applications is nitrous oxide. When soil conditions become anaerobic—from moisture associated with irrigation, rain events, or manure applications—in the presence of high nitrogen concentrations, microbes will choose to respire using nitrate (NO3-) as their primary metabolic source. When NO3- is respired by microorganisms, nitrate is broken down in the process of denitrification. The primary end-product of the denitrification process is nitrous oxide.
Three common land application strategies are used in the United States--broadcast application, injection, and banded manure application. Research has shown that though the most effective agronomically to efficiently make nitrogen resources from manure available to plants is manure injection or manure incorporation, however, these practices have proven to be the highest nitrous oxide producers from literature reviews. When manure is injected or incorporated, microbes have greater access to nitrogen sources, which results in higher denitrification and associated greenhouse gas emissions. Broadcast applications of manure are agronomically limiting, especially if rainy areas, which may wash away manure sources before it is utilized by plants as a fertilizer. Conclusively, we found that manure banding, which limits soil-manure interactions, is the most effective mitigation technique for manure application.
Unprocessed dairy manure is most commonly broadcast applied to crop and forage land as the least labor intensive option for dairy producers. Broadcast application requires loading raw manure into spreaders or tractors, which are then driven over fields at relatively high speeds, with manure thrown from the spreaders. There are many draw backs to this system; manure cannot be applied at variable rates and in many cases, manure can be unevenly applied. To improve nitrogen use efficiency and reduce immediate nitrogen losses as ammonia volatilization from soil, many land managers will till in, or incorporate, manure after broadcast application. Though manure is commonly incorporated, incorporation increases nitrous oxide emissions because manure is immediately placed into soil at depth, where anaerobic (oxygen limited) zones are more likely to develop.
When manure is separated, liquid slurry manure can be injected into the soil surface, immediately placing the manure into the root zone at depth, where nitrogen is immediately available to plants. Slurry injection is advantageous because it is more cost efficient than hauling and spreading raw manure and does not require additional labor if manure has already been separated (Plastina and Johanns 2015). However, like incorporated manure, slurry injection results in increased anaerobic conditions, which promote nitrous oxide emissions. A 2015 study by Hou et al. found that manure slurry injection is responsible for a significant increase in nitrous oxide emissions, though carbon dioxide emissions decreased from this application treatment. This finding make manure injection a poor choice for greenhouse mitigation strategies.
Banded application of manure is the most effective means of manure application for agronomic nitrogen efficiency and greenhouse gas emissions. Manure banding places bands strategically between planted rows of crops, which allows the rooting systems immediate access to manure nutrient resources. Because manure is applied in bands, it is not widely spread across the field, and by limiting the soil-manure contact area, greenhouse gas emissions can be reduced from this system because the manure is not easily accessed by microorganisms that can break it down to produce nitrous oxide.
Influential Manure Management Factors
EnvironmentalCurrent environmental regulations that drive manure handling processes limit all manure application by the amount of phosphorus present in the manure. Phosphorus is a primary concern for the Wisconsin Department of Natural Resources because as phosphorus is loaded into water that leaves farms and contributes to local, regional, and national watershed eutrophication in lakes, streams, and even the Gulf of Mexico. Eutrophication is detrimental to all aquatic communities, influencing fish populations, algal blooms, water temperature, and many other attributes that reduce overall water quality (Sturgul and Bundy 2004). Because phosphorus exists in very high concentrations in dairy manure, farmers must carefully monitor the amount of phosphorus applied, because large dairy farms are considered to be a point source of phosphorus pollution to water systems. Current regulations say that no more than 50 ppm P can be present in soil at any given time. Because liquid manure slurry is much lower than solid manure in P concentrations, this gives farmers some incentive to separate their manure stores, which consequently can reduce their greenhouse gas emission loads if handled properly (Sturgul and Bundy 2004).
Another issue of significant concern in areas with manure spreading is nitrate loading in groundwater. If nitrate is not taken up by plants or denitrified into a gaseous form, nitrate is easily leached from the soil’s root zone and in high concentrations (greater than 10% by volume), can lead to methemoglobinemia, or blue baby syndrome, a condition that converts nitrate into nitrite in infants, which results in the babies to become poisoned and their blood is inable to support oxygen (Bundy and Jackson 2004). Though rare, this is a huge health safety concern for the state of Wisconsin.
SocialLarge scale dairy farms often have more manure produced each year than they have land to spread that manure on. To facilitate manure removal from their farms, dairy producers need community support from their neighboring farmers, particularly grain crop producers. In theory, by creating partnerships between grain and dairy farmers, both will receive benefits to their management systems; dairy farmers are able to remove manure from storage on their farms and grain producers have access to a relatively cheap, organic fertilizer source. However, there has been a historic cultural reluctance for grain farmers to partner with neighboring dairy farms for fertilizer products (Sanford et al. 2009). Though results of research trials studying grain yield productivity from these six Wisconsin farms showed promising increased in yields, farmers were hesitant to continue manure sharing practices with dairy farms due to concerns about manure availability, slurry run-off, costs of manure spreading, and environmental concerns of increasing nitrate and phosphorus levels from manure applications (Sanford et al. 2009). These concerns can create manure storage bottlenecks, which can limit a dairy farm’s ability to grow and maximize its production.
Solid Manure Management
Slurry Manure ManagementSlurry manure is most effectively mitigated by acidifying manure during storage, applying storage covers --like straws or synthetic oils, and routinely emptying the slurry tank to reduce bacterial loads, and applying manure in liquid bands. No matter the case, slurry manure application resulted in higher greenhouse gas emissions than solid manure land application, because liquids are more volatile when applied. Though the most efficient by agronomic N standards, manure injection results in the highest emissions source, and the most effective mitigation strategy was manure band spreading, to reduce the surface area of soil-slurry interface.
- Manure management is reliant on the type of existing management infrastructure. Solid-liquid separation allows for the most potential mitigation adjustments to each physical manure pool, and is the most versatile system.
- In every instance examined, capturing emissions by covering or sealing manure resulted in higher mitigation potential.
- Cool, dry manure produces the least amount of total emissions.
Paper for Journal Club
Check out the paper we will discuss in class on Tuesday at this link.
Hey Fellow Food System Sustainability Classmates! We realize this article by Montes et al. is pretty lengthy, so we thought we'd give you some pointers to get ready for discussion this Tuesday. Please use the instructions below to guide your reading:
- Read thoroughly the Abstract and Introduction
- "Livestock Manure and Emissions": study up on Figures 1 and 2
- Skip "Animal Mangagement and Housing" but take look at Table 1
- Get the gist of "Manure Management and Treatment"
See you Tuesday!
CitationsAguerre MJ, Wattiaux MA, Powell JM (2012) Emissions of ammonia, nitrous oxide, methane, and carbon dioxide during storage of dairy cow manure as affected by dietary forage-to-concentrate ratio and crust formation. Journal of Dairy Science 95:7409–7416. doi: 10.3168/jds.2012-5340
Aguirre-Villegas HA, Passos-Fonseca TH, Reinemann DJ, et al (2015) Green cheese: Partial life cycle assessment of greenhouse gas emissions and energy intensity of integrated dairy production and bioenergy systems. Journal of Dairy Science 98:1571–1592. doi: 10.3168/jds.2014-8850
Andeweg K, Reisinger A, Sustainable Agriculture Initiative Platform, et al (2014) Reducing greenhouse gas emissions from livestock: best practice and emerging options.
Beddoes J, Bracmort K, Burns R, Lazarus W (2007) An Analysis of Energy Production Costs from Anaerobic Digestion Systems on U.S. Livestock Production Facilities.
Bundy L, Jackson G (2004) Nitrate in Wisconsin Groundwater: Sources and concerns.
Burke D (2001) Dairy Waste Anaerobic Digestion Handbook: Options for Recovering Beneficial Products From Dairy Manure. Environmental Energy Company 1–57.
Davis C (2008) Capacity Development: Empowering People and Institutions, Annual Report 2008. United Nations Development Programme
Environmental Protection Agency (2015) Calculations and References | Clean Energy | US EPA. In: Clean Energy. http://www.epa.gov/cleanenergy/energy-resources/refs.html. Accessed 12 May 2015
Food and Agriculture Organization (2013) Tackling climate change through livestock: a global assessment of emissions and mitigation opportunities. FAO, Rome
Hénault C, Grossel A, Mary B, et al (2012) Nitrous oxide emission by agricultural soils: a review of spatial and temporal variability for mitigation. Pedosphere 22:426–433.
Hou Y, Velthof GL, Oenema O (2015) Mitigation of ammonia, nitrous oxide and methane emissions from manure management chains: a meta-analysis and integrated assessment. Global Change Biology 21:1293–1312. doi: 10.1111/gcb.12767
Lazarus W (2013) Economics of Anaerobic Digesters for Processing Animal Manure - eXtension. http://www.extension.org/pages/19461/economics-of-anaerobic-digesters-for-processing-animal-manure#.VTU-CSFViko. Accessed 20 Apr 2015
Maeda K (2015) Nitrous oxide emissions from dairy manure compost. Japan Agriculture Research Quarterly 49:17–21.
Marañón E, Salter AM, Castrillón L, et al (2011) Reducing the environmental impact of methane emissions from dairy farms by anaerobic digestion of cattle waste. Waste Management 31:1745–1751. doi: 10.1016/j.wasman.2011.03.015
Mehta A (2002) The economics and feasibility of electricity generation using manure digesters on small and mid-size dairy farms.
Montes F, Meinen R, Dell C, et al (2013) SPECIAL TOPICS—mitigation of methane and nitrous oxide emissions from animal operations: II. A review of manure management mitigation options. Journal of animal science 91:5070–5094.
O’Brien D, Capper JL, Garnsworthy PC, et al (2014) A case study of the carbon footprint of milk from high-performing confinement and grass-based dairy farms. Journal of Dairy Science 97:1835–1851. doi: 10.3168/jds.2013-7174
Owen JJ, Silver WL (2015) Greenhouse gas emissions from dairy manure management: a review of field-based studies. Global Change Biology 21:550–565. doi: 10.1111/gcb.12687
Parkin TB, Venterea RT (2010) USDA-ARS GRACEnet Project Protocols Chapter 3. Chamber-Based Trace Gas Flux Measurements 4. Sampling Protocols USDA-ARS, Fort Collins, CO 3–1.
Petersen SO, Blanchard M, Chadwick D, et al (2013) Manure management for greenhouse gas mitigation. Animal 7:266–282. doi: 10.1017/S1751731113000736
Plastina A, Johanns A (2015) 2015 Iowa Farm Custom Rate Survey. Iowa State University, Extension and Outreach File A3-10. Ames, Iowa
Sanford GR, Cook AR, Posner JL, et al (2009) Linking Wisconsin Dairy and Grain Farms via Manure Transfer for Corn Production. Agronomy Journal 101:167. doi: 10.2134/agronj2008.0126
Shepherd T (2010) Cost to produce dairy manure solids bedding. Pro-Dairy: Eastern Dairy Business
Sturgul S, Bundy L (2004) Understanding Soil Phosphorus: An overview of phosphorus, water quality, and agricultural management practices.
Viguria M, Sanz-Cobeña A, López DM, et al (2015) Ammonia and greenhouse gases emission from impermeable covered storage and land application of cattle slurry to bare soil. Agriculture, Ecosystems & Environment 199:261–271. doi: 10.1016/j.agee.2014.09.016
Wood JD, VanderZaag AC, Wagner-Riddle C, et al (2014) Gas emissions from liquid dairy manure: complete versus partial storage emptying. Nutrient Cycling in Agroecosystems 99:95–105. doi: 10.1007/s10705-014-9620-2
Van der Weerden TJ, Luo J, Dexter M (2014) Addition of Straw or Sawdust to Mitigate Greenhouse Gas Emissions from Slurry Produced by Housed Cattle: A Field Incubation Study. Journal of Environment Quality 43:1345. doi: 10.2134/jeq2013.11.0452
Meet the Team!
Hi, we're Claire and Jordan, students at the University of Wisconsin interested in mitigation strategies for dairy production in Wisconsin.
Jordan is a junior Dairy Science undergraduate student. He comes from his family's 3,000 cow commercial dairy farm in Northeastern Wisconsin. His family's farm is actively seeking strategies and technologies to further decrease the effects of manure on the environment and community. In his free time, Jordan enjoys watching and playing basketball and other sports, along with showing dairy cattle and maintaining a strong interest in agriculture.
Claire is a second year graduate student in the Department of Soil Science. When she's not petting cows, she's studying greenhouse gas mitigation strategies associated with manure land applications from dietary feeding trials for dairy cows. Originally from Tennessee, Claire has lived in South Carolina and Arizona before ending up in Wisconsin. In her spare time, she enjoys bike riding through Wisconsin's dairy land, reading good books, and hiking.