Category: Climate and Ag

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Sustainability of the Dairy Industry in the United States

Purpose

The U.S. dairy industry recognizes its environmental impact and has committed to achieving carbon neutrality by 2050, aiming to significantly reduce greenhouse gas (GHG) emissions while maintaining production efficiency. The primary sources of dairy-related emissions include enteric methane from cows, manure management, feed production, and energy use on farms.

Improvements in feed efficiency and manure management have already led to reductions in emissions per unit of milk produced. For instance, Idaho has successfully reduced enteric methane emissions per unit of milk by 25% since 1990, and methane emissions from manure per unit of milk have declined by about 20% (O’Hara, 2022). However, the total emissions from manure have increased by 20% due to herd growth in Idaho. These figures highlight the challenge of balancing productivity with environmental stewardship. Despite these difficulties, advancements in animal nutrition, manure management, and emerging technologies provide a promising path toward sustainability.

What Did We Do?

Over the past several decades, remarkable advancements in dairy farming have significantly improved milk production efficiency. Since the 1940s, the industry has nearly quadrupled milk output per cow through genetic improvements, optimized nutrition, and better overall management. This increase in productivity has allowed farmers to produce more milk with fewer cows, reducing the environmental footprint of each unit of dairy produced. Beyond improvements in feed efficiency, nutritional interventions such as adding feed additives like 3-NOP (3-nitrooxypropanol), seaweed, and oilseeds have been shown to reduce enteric methane emissions by altering rumen microbial activity. Research suggests that 3-NOP, for instance, can reduce methane emissions by up to 30% without negatively affecting milk yield or composition (Hristov, 2021).

Manure management is another critical area of focus. Technologies such as anaerobic digesters, composting systems, and improved storage techniques have been implemented to mitigate methane emissions from manure. Anaerobic digesters convert manure into biogas, which can be used as a renewable energy source, reducing the reliance on fossil fuels and lowering overall carbon emissions. Other strategies, such as mechanical separators and compost-bedded pack barns, have also been explored as effective methods for reducing methane release from stored manure.

What Have We Learned?

Several key strategies have emerged as effective pathways for improving dairy sustainability. The first is continued advancements in genetics, which allow farmers to breed more productive cows that require fewer resources per unit of milk produced. Selective breeding programs targeting low-methane-emitting cows could further contribute to sustainability efforts. Precision feeding techniques, which ensure cows receive the optimal balance of nutrients without overfeeding, are also crucial for reducing emissions. Feed additives such as tanniferous forages, alternative electron sinks like nitrates, and certain types of fats have shown potential in mitigating enteric methane production. However, long-term research is still needed to assess their effectiveness and potential side effects on animal health and productivity.

Another significant finding is the role of manure management systems in influencing overall farm emissions. Studies indicate that farms implementing covered liquid slurry storage and anaerobic digesters experience lower methane emissions compared to traditional open-lagoon systems. Additionally, manure treatment systems that integrate composting or separation techniques have been identified as key factors in reducing GHG emissions. Beyond farm-level practices, the industry has recognized the importance of collaboration across the supply chain. Processors, retailers, and policymakers must work together to promote sustainable practices, invest in research, and provide incentives for farmers to adopt new technologies.

Future Plans

Moving forward, the dairy industry will continue to focus on increasing milk production efficiency as a means of reducing emissions per unit of milk produced. Advances in genetics, feed optimization, and herd management will further contribute to sustainability efforts. Additionally, manure management will play a pivotal role in achieving sustainability goals. Expanding the use of anaerobic digesters and nutrient recycling technologies will help reduce emissions while providing renewable energy and valuable soil amendments.

Investment in research and innovation will be essential for identifying new strategies and improving existing ones. Research into alternative feed additives, precision agriculture, and digital monitoring tools will enable farmers to make data-driven decisions that enhance both productivity and environmental sustainability. Policy support and financial incentives will also be critical in accelerating the adoption of sustainable practices. Government programs and industry initiatives should continue to provide funding for technology adoption, carbon offset programs, and educational resources for farmers. Ultimately, the U.S. dairy industry is well-positioned to make significant strides toward its sustainability goals. By leveraging innovation, research, and collaboration, the industry can continue to provide essential nutrition while reducing its environmental footprint and working toward carbon neutrality by 2050.

Authors

Presenting & corresponding author

Mark A. McGuire, University Distinguished Professor, Department of Animal, Veterinary and Food Sciences, University of Idaho, mmcguire@uidaho.edu

Additional Information

Capper, J. L., Cady, R. A., & Bauman, D. E. (2009). The environmental impact of dairy production: 1944 compared with 2007. Journal of Animal Science, 87(6), 2160–2167. https://doi.org/10.2527/jas.2009-1781

El Mashad, H. M., Barzee, T. J., Franco, R. B., Zhang, R., Kaffka, S., & Mitloehner, F. (2023). Anaerobic digestion and alternative manure management technologies for methane emissions mitigation on Californian dairies. Atmosphere, 14(1), 120. https://doi.org/10.3390/atmos14010120

Godber, O. F., Czymmek, K. J., van Amburgh, M. E., & Ketterings, Q. M. (2024). Farm-gate greenhouse gas emission intensity for medium to large New York dairy farms. Journal of Dairy Science. https://doi.org/10.3168/jds.2024-25874

Hristov, A. N., Melgar, A., Wasson, D., & Arndt, C. (2021). Symposium review: Effective nutritional strategies to mitigate enteric methane in dairy cattle. Journal of Dairy Science, 105(10), 8543–8557. https://doi.org/10.3168/jds.2021-21398

Innovation Center for U.S. Dairy. (2022). U.S. Dairy Sustainability Report 2021-2022. Retrieved from https://www.usdairy.com/about-us/innovation-center

Kreuzer, M. (2024). Feed additives for methane mitigation: Introduction—Special issue on technical guidelines to develop feed additives to reduce enteric methane. Journal of Dairy Science.

Nguyen, B. T., Briggs, K. R., & Nydam, D. V. (2023). Dairy production sustainability through a one-health lens. Journal of the American Veterinary Medical Association, 261(1). https://doi.org/10.2460/javma.22.09.0429

O’Hara, J. K. (2022). State-level trends in the greenhouse gas emission intensity of U.S. milk production. Journal of Dairy Science, 106(10), 5474–5484. https://doi.org/10.3168/jds.2022-22741

Rotz, C. A. (2017). Modeling greenhouse gas emissions from dairy farms. Journal of Dairy Science, 101(7), 6675–6690. https://doi.org/10.3168/jds.2017-13272

U.S. Farmers & Ranchers in Action (USFRA). (2024). Potential for U.S. Agriculture to Be Greenhouse Gas Negative. Retrieved from https://www.usfraonline.org

Acknowledgements

Supported by USDA-NIFA SAS 2020-69012-31871

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Bang for Your Buck: Developing Effective Anaerobic Digestion Policies for Carbon Emission Reduction

Purpose

Anaerobic digesters are an established technology for reducing methane emissions from livestock manure. In recent years, the rapid expansion of renewable natural gas (RNG) projects, driven by economic incentives such as Renewable Identification Number (RIN) credits, Low Carbon Fuel Standard (LCFS) credits, and Investment Tax Credits (ITC) from the 2022 Inflation Reduction Act, has spurred significant growth in RNG production. These incentives, while promoting the adoption of anaerobic digestion, may only sometimes be the most cost-effective way to achieve meaningful carbon reductions within the livestock sector. RNG production, electricity generation via biogas, and flaring biogas all mitigate agricultural greenhouse gas (sometimes referred to as carbon dioxide equivalence or CO2e) emissions from manure.  Nonetheless, electric generators are significantly cheaper than the biogas upgrading systems necessary for RNG production, and flares are significantly cheaper than electric generators.

Our analysis compares system costs and emissions reductions, and investigates the societal benefit featured by each system. The only revenue we analyze is RNG sales and electricity sales; we do not incorporate carbon credits into the revenue stream. Flaring biogas, or the process of burning the methane within biogas to produce the lesser potent greenhouse gas, CO2, greatly reduces agricultural CO2e emissions, though this process does not generate usable renewable energy. Electricity generation via biogas is cheaper than RNG production via biogas, but electricity can be sustainably generated with more efficient methods, such as wind turbines and solar panels. RNG is primarily created via anerobic digestion; additionally, RNG is the leading renewable replacement for conventional natural gas, a fossil fuel with increasing use, traveling within 3,000,000 miles of pipelines in the U.S. Nonetheless, RNG remains an expensive and technically complex process, requiring high capital investment and persistent, local, and skilled labor for effective operation.

What Did We Do?

This study compares the economic and carbon reduction potential of various anaerobic digestion biogas uses, including RNG production, electricity generation, and flaring. By evaluating the carbon savings and cost-effectiveness of these options, the study provides policymakers insights on optimizing public funding and incentives for the livestock industry. Furthermore, we provide livestock farmers with a decision support tool that balances the environmental benefits of anaerobic digestion with the most efficient use of financial resources to foster clean and sustainable livestock production system.

What Have We Learned?

Table 1 summarizes dollars per megagram (MG) of CO2e mitigated via RNG production, electricity production via biogas, and flaring biogas for both covered manure storages and constructed anaerobic digesters. Five scenarios were compared for farms featuring dairy cows, swine with lagoon manure storages, and swine with deep pit manure storages to analyze the carbon credit value (units of dollars per MG of CO2e mitigated) necessary to financially break even on the project. Flaring biogas featured the lowest necessary break-even carbon credit for dairy, swine farms with lagoon manure storage, and swine farms with deep pit manure storages. If a farmer wants to generate power, then generating electricity requires a lesser carbon credit value per MG CO2e mitigated compared to RNG generation. If a farmer wants to generate power via RNG, and carbon credits exist in units of dollars per energy, then a dairy farmer would be more profitable with a digester, whereas a swine farmer would be more profitable with a covered manure storage.

If a governing body is interested in maximizing its livestock manure CO2e reduction given a set amount of tax dollars, then the governing body may be most interested in incentivizing flaring systems. If a governing body is interested in both power generation via livestock manure and CO2e reduction, then the governing body may be most interested in incentivizing electricity generation. Nonetheless, renewable electricity can be generated more efficiently by a variety of methods, whereas RNG is the most prominent fossil natural gas replacement and primarily created via anaerobic digestion. Furthermore, as the electric grid “greens”, or as the CO2e emissions associated with grid electricity decrease, RNG generation will provide an overall greater percent CO2e reduction.

Deep pit swine farms generating electricity or RNG demonstrated CO2e reduction that was greater than 100%. Deep pit swine farms have less emissions than lagoon swine farms. By converting a deep pit swine farm to an outdoor covered manure storage or digester system, methane production increases, though that methane is now used for renewable energy generation, thereby offsetting fossil energy generation.

Table 1: Required Carbon Credit Value ($/MG CO2e mitigated) to Break Even
Head Dairy: 2,000 Swine – Lagoon: 14,000 Swine – Deep Pit: 14,000
Baseline CO2e (MG/yr) 10,654 10,179 3,980
Covered Storage Flaring CO2e Mitigated (MG/yr) 8,786 8,786 3,424
% CO2e Reduction 82% 86% 86%
$/yr Profit (10-year life) ($84,137) ($108,151) ($342,975)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $10 $12 $100
Covered Storage Electricity CO2e Mitigated (MG/yr) 9,734 9,735 4,373
% CO2e Reduction 91% 96% 110%
$/yr Profit (10-year life) ($178,978) ($202,992) ($437,816)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $18 $21 $100
Break-Even ($/kWh) Carbon Credit $0.08 $0.09 $0.20
Covered Storage RNG CO2e Mitigated (MG/yr) 9,913 9,914 4,552
% CO2e Reduction 93% 97% 114%
$/yr Profit (10-year life) ($780,801) ($795,726) ($1,030,551)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $79 $80 $226
Break-Even ($/MMBTU) Carbon Credit $46 $47 $61
Digester Electricity CO2e Mitigated (MG/yr) 10,042 9,826 4,464
% CO2e Reduction 94% 97% 112%
$/yr Profit (10-year life) ($557,022) ($519,566) ($754,390)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $55 $53 $169
Break-Even ($/kWh) Carbon Credit $0.14 $0.19 $0.27
Digester RNG CO2e Mitigated (MG/yr) 10,169 9,904 4,542
% CO2e Reduction 95% 97% 114%
$/yr Profit (10-year life) ($1,207,287) ($1,056,809) ($1,291,633)
Break-Even ($/MG CO2e Mitigated) Carbon Credit $119 $107 $284
Break-Even ($/MMBTU) Carbon Credit $39 $50 $62

Future Plans

The project life of biogas upgrading equipment, pipeline interconnects, electric generators, and flares are not always the same. We intend to further investigate the project lives of different equipment to calculate more accurate annualized costs and payback periods. Furthermore, we will analyze how the economies of scale compare between biogas upgrading equipment, electric generators, and flares by evaluating costs of equipment necessary for various farm sizes. Lastly, we would like to further define and quantify the overall societal impact created by RNG production, electricity production via biogas, and flaring biogas.

Authors

Presenting author

Luke Soko, Graduate Student, Iowa State University

Corresponding author

Dan Andersen, Associate Professor, Iowa State University, dsa@iastate.edu

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date. 

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Livestock Emissions in the United States: Challenges, Efforts, and Opportunities

Due to a technical glitch, we did not get this presentation recorded. Please accept our apologies.

Purpose

This study aimed to review current literature on livestock emissions in the United States, focusing on sources, challenges, and mitigation strategies. Specifically, it examines emissions from enteric fermentation, animal housing, manure management systems, and manure utilization. By synthesizing existing research, the study provides an understanding of how these emission sources contribute to air quality concerns, including greenhouse gas accumulation, odor issues, and public health risks. Additionally, it highlights the regulatory landscape and ongoing efforts to monitor and reduce emissions through technological and management innovations.

This study also explores opportunities for improving air quality while maintaining sustainable livestock production. It evaluates the effectiveness of various mitigation strategies, such as precision feeding, anaerobic digestion, and advanced manure treatment systems, in reducing emissions. Furthermore, it discusses potential advancements, including circular economy approaches and enhanced air quality modeling, to optimize emission reductions. By providing this analysis of current research and policy efforts, this study aims to support informed decision-making among producers, researchers, and policymakers in advancing sustainable livestock systems.

What Did We Do?

This literature review analyzed peer-reviewed research, government reports, and industry publications on livestock emissions. The review focused on emissions from enteric fermentation, animal housing, manure management systems, and manure utilization, identifying key sources and their environmental impacts. Studies were selected based on their relevance to air quality, greenhouse gas emissions, and mitigation strategies, ensuring a broad yet detailed assessment of current knowledge. Additionally, regulatory frameworks and policies from agencies such as the United States Department of Agriculture  and U.S. Environmental Protection Agency were examined to contextualize efforts aimed at reducing emissions in livestock production systems.

To evaluate mitigation strategies, the study categorized technologies and management practices based on their effectiveness, feasibility, and adoption rates. Approaches such as anaerobic digesters, biofilters, precision feeding, and manure treatment systems were reviewed for their potential to reduce emissions while maintaining economic viability. Case studies and data from ongoing research projects were incorporated to highlight real-world applications and emerging innovations. The synthesis of findings aimed to identify knowledge gaps, assess the impact of existing policies, and propose future research directions to enhance emission reduction efforts in livestock production.

What Have We Learned?

Livestock emissions primarily arise from enteric fermentation (methane from digestion) and manure management. These sources contribute significantly to agricultural methane emissions, a potent greenhouse gas impacting climate change. Recent research has enhanced our understanding of strategies to mitigate methane emissions from livestock, particularly through dietary interventions. Feed additives like 3-nitrooxypropanol (3-NOP) and red seaweed (Asparagopsis taxiformis) have shown significant potential in reducing methane production during digestion. Studies indicate that 3-NOP can decrease methane emissions by approximately 30% in dairy cows, while red seaweed has been shown to reduce emissions by up to 80% in beef cattle. These additives work by inhibiting specific enzymes involved in methane synthesis within the rumen, thereby lowering the overall greenhouse gas output from ruminant livestock.

In addition to dietary strategies, advancements in manure management have been explored to further reduce environmental impacts i.e., solid-liquid separation, anaerobic digestion, acidification, vermifiltration. Anaerobic digestion (AD) systems convert livestock manure into biogas, which can be used as a renewable energy source. This process not only mitigates methane emissions but also offers economic benefits by reducing fossil fuel expenses and generating income from excess energy production. However, the economic viability of AD systems can be influenced by factors such as operational costs and the scale of implementation. Therefore, while AD presents a promising approach to sustainable manure management, careful consideration of these factors is essential for its successful adoption in livestock operations.

Future Plans

Future studies on mitigating dairy emissions should focus on integrated approaches across enteric fermentation, manure management, and land application. Research into dietary interventions, such as precision feeding strategies and methane-reducing feed additives like seaweed, tannins, and essential oils, could help lower enteric methane emissions while maintaining animal productivity. Advances in microbiome research could further refine these approaches by identifying specific gut microbial populations that reduce methane production. Additionally, long-term studies on genetic selection for low-methane-emitting cattle could offer a sustainable mitigation strategy without compromising milk yield.

For manure systems and applications, future research should prioritize optimizing anaerobic digestion efficiency to maximize methane capture and energy recovery while reducing residual emissions. Innovative manure amendments, such as biochar or nitrification inhibitors, could limit methane and nitrous oxide release during storage and land application. Studies on precision manure application techniques, including low-disturbance injection and variable-rate spreading, could enhance nutrient use efficiency while minimizing emissions. Furthermore, landscape-scale modeling should be developed to assess the cumulative effects of these strategies and guide policy recommendations for sustainable dairy farming.

Authors

Presenting & corresponding author

Gilbert Miito, Assistant Professor & Extension Specialist — Air Quality, University of Idaho, gmiito@uidaho.edu

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date. 

 

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Effective community co-creation approaches for livestock manure management

Due to a technical glitch, we did not get this presentation recorded. Please accept our apologies.

Purpose

Climate solutions are often talked about in a vacuum and conversation participants can sometimes overlook unintended consequences upon local environment and health. Solutions to mitigate methane from livestock agriculture are no exception to these climate discussions, and can impact other potential pollutants including ammonia, nitrous oxide, and odors. Moreover, it can be a particularly difficult space to work in climate and environmental justice, as many different communities are seemingly villainized and pit against each other, which make climate solutions even harder to implement.

What Did We Do?

Environmental Defense Fund is in the midst of an ongoing pilot project to engage communities in workshops around solutions regarding manure management. The goal of these workshops is to demonstrate best practices for effective collaboration and solution co-creation between farmers/producers and communities that can then be taken to local policymakers and stakeholders to implement. In this way, we can co-create solutions that align with community concerns, climate change mitigation, and feasibility for farmers.

What Have We Learned?

Community co-creation is possible, and even stakeholders who may seem hyper-polarized can still sit together at the same table to work together with ample time, transparency, and trust. Policy implications are enormous here and this session will discuss learnings we have regarding common misconceptions and myths around working with different affected stakeholders, as well as necessary guardrails surrounding commonly discussed methane mitigation technologies.

Future Plans

We will continue to work with the affected communities, including community groups and producer groups, to find common ground, with the hope of making these processes shareable across the country.

Authors

Presenting & corresponding author

Mindi W. DePaola; Senior Manager, Community and Equity, Ag Methane; Environmental Defense Fund, mdepaola@edf.org

Acknowledgements

We’d like to thank groups who have continued to give us time, as time is the biggest resource. These groups include White Earth Nation, EJCAN, Leadership Counsel for Environmental Justice, and MN Milk. NOTE: these are not necessarily official partners but again, want to acknowledge their time spent meeting with EDF.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.

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The Economics of Carbon Markets for Dairy Industry

Purpose

Dairy farmers in Washington state have been under significant pressure to reduce their carbon footprint in recent years. Dairy cooperative sustainability initiatives such as achieving carbon neutrality by 2050 have left many producers wondering what will be required of them to help their cooperatives meet this goal. Coupled with regulatory pressures to report on their greenhouse gas emissions and the threat of regulation to reduce them, uncertainty remains for producers around the types of climate-smart practices that will enable them to reduce their carbon footprint while remaining economically viable.

Without a thorough understanding of the costs and risks, pressures, or requirements to implement climate-smart practices may inadvertently drive consolidation and the accelerated loss of small to medium sized farms.

What Did We Do?

Utilizing Washington state dairy facility data, I conducted an economic cost benefit analysis of two climate-smart practices that capture GHGs from anaerobic storage: anaerobic digestors and the covered lagoon and flare system and the size of operation needed to implement both practices based on current and historic market conditions and technology costs. Private and public investment in climate-smart practices can have a substantial impact on whether they are economically feasible for producers to implement. I considered the impacts of various levels of cost-share on the size of farm able to adopt the technology based on several economic indicators.

What Have We Learned?

Most dairy farms cannot simply raise their prices to offset the costs of climate-smart practices, therefore it is critical to understand the broad economic impacts of imposing emissions reductions mandates. With consolidation being a well-documented trend across dairy farms in the United States, it is possible that climate regulations will only further exacerbate this trend due to the high capital costs and market risk associated with climate-smart farming that only facilities of scale can take on.

Future Plans

I am actively assisting research right now in Washington state with university and private researchers into dairy farm carbon intensities, across various farm sizes and facility types. An overview of this research may be available by Summer of 2025. Once this work is completed, we will have a better understanding of overall farm emissions and what climate-smart practices may be necessary for farms to implement to help achieve cooperative net zero targets.

Authors

Presenting & corresponding author

Nina Gibson, Agricultural Economist and Policy Specialist, Washington State Department of Agriculture, KGibson@agr.wa.gov

Additional Information

Link to Podcast I hosted, the Carbon and Cow$ Podcast, which covers the risks and opportunities associated with carbon markets for dairy and livestock producers: https://csanr.wsu.edu/program-areas/climate-friendly-farming/carbon-and-cows-podcast/

Link to my program’s homepage at WSDA: https://agr.wa.gov/manure

My Linkedin: https://www.linkedin.com/in/nina-gibson-b482a8119/

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.

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Measured methane emission rates relative to the chemical composition of dairy manure samples

Purpose

Methane emissions from liquid manure storage systems contribute a significant portion of methane emissions from the US agricultural sector (EPA, 2024). There is a need for more farm-level methane emission values to guide decision-making activities within the dairy industry and by government agencies. Cost, time, and labor constraints are challenges related to on-farm methane emission measurements. There is a need for simpler emission measurement methods.

The purpose of this work was to investigate relationships between methane emission rates (MER) in a laboratory assay and commonly measured characteristics including total solids (TS), volatile solids (VS), ash, and total Kjeldahl nitrogen (TKN). The relationships were also examined in conjunction with storage type, season, manure type, and storage duration.

What Did We Do?

We collected dairy manure samples from manure storages at 27 farms in Minnesota and Wisconsin at 2 to 4-month intervals throughout 2024. These samples represented various storage types, storage durations, and manure temperatures. To date, a majority of these samples have been processed for TS, VS, Ash, and TKN using standard methods for manure chemical analyses (American Water Works Association, 2017; Wilson et al., 2022). Additionally, MER were estimated in triplicate with a 3-day in vitro assay (Andersen et al., 2015). Relationships between MER and these manure chemical constituents were examined using Spearman correlation analysis and bivariate plots across all manure samples and with respect to other manure management characteristics. These include storage type, season, manure type, and storage duration. Manure chemical constituents were treated as numerical data whereas storage characteristics were treated as categorical data in the analysis. It is important to note that many samples may only have a partial set of manure analyses completed at this point. This resulted in varying counts of available samples used in the statistical analyses below (Table 1-3). Summary statistics (mean, median, range) are also presented for the different manure chemical constituents.

What Have We Learned?

Table 1 shows summary statistics of dairy manure samples processed for this work (wet basis). There was a wide range of concentrations observed for each manure chemical constituent; however, average values were comparable to American Society of Agricultural and Biological Engineers (ASABE) manure characteristics values (ASABE, 2019).

Table 1: Summary statistics of dairy manure chemical characteristics (% wet basis) (n = 148 for TKN, n = 155 for other manure constituents)

Mean Median Min Max
TS 5.92% 4.98% 0.53% 17.89%
VS 4.39% 3.50% 0.27% 16.60%
Ash 1.53% 1.21% 0.26% 11.12%
TKN 0.31% 0.29% 0.08% 0.83%

Generally, overall correlations (Table 2) and correlations within categories (Table 3) were not strong, however there were some exceptions. These exceptions were observed in TS and VS relationships with MER for flush water and long-term storage duration (Table 3). Here, both positive and negative correlations that were at least moderately strong (rs ≥ |0.5|) were observed. Since methane emissions are a product of organic matter degradation, positive correlations between VS and MER were expected, but not always reflected in the results. Other trends in relationships between other manure constituents and MER are not well understood. However, manure management factors may also influence other microbial activity with respect to TS, Ash, and TKN content, which may have indirect effects on MER that cannot be discerned from a correlative relationship.

Additionally, given the wide range in the concentrations of all manure constituents and MER, it may be difficult to distinguish these relationships when comparing across the aggregate values. Instances where the strongest correlations were observed (Table 3) describe samples from a single farm, which suggests conducting a similar analysis within individual farms to better understand these relationships.

Table 2: Overall Spearman correlation values (rs) between manure constituents and MER

Total solids Volatile solids Ash Total Kjeldahl Nitrogen
MER 0.060 0.052 0.137 -0.046

 

Table 3: Spearman correlation values (rs) between manure constituents and MER by manure storage type, manure type, storage duration, and season

TS vs MER VS  vs MER Ash vs MER TKN vs MER
Manure storage type Transfer pit (n = 169) 0.150 0.124 0.271 0.075
Underfloor pit (n = 34) -0.103 -0.121 -0.125 -0.153
Manure type Raw manure (including bedding (n=36) 0.270 0.267 0.312 0.369
Raw manure (including bedding + others) (n = 140) 0.042 0.047 0.094 -0.093
Liquid separated manure (n =24) -0.213 -0.297 -0.025 -0.156
Flush water (n = 9) 0.800 0.800 0.883 0.833
Storage duration Short term (< 1 month) (n = 176) 0.082 0.090 0.117 -0.020
Long term (> 1 month) (n =6) -0.771 -0.771 -0.143 -0.200
Point sample (not a storage) (n= 29) 0.029 -0.078 0.350 -0.136
Season Winter (n= 23) 0.013 0.081 -0.011 0.132
Spring (n= 57) 0.406 0.399 0.411 0.238
Summer (n = 46) -0.268 -0.291 -0.165 -0.436
Fall (n =66 -0.188 -0.198 -0.023 -0.011

 Future Plans

We plan to conduct a stepwise regression analysis to better understand the significant independent variables (manure constituents) that influence MER. Correlations between manure constituents and MER using measurements from samples within individual farms will also be conducted.

Authors

Presenting author

Noelle Soriano, PhD candidate, University of Minnesota

Corresponding author

Erin Cortus, Associate Professor and Extension Engineer, University of Minnesota, Ecortus@umn.edu

Additional author

MaryGrace Erickson, Postdoctoral associate, University of Minnesota

Additional Information

Andersen, D. S., Van Weelden, M. B., Trabue, S. L., & Pepple, L. M. (2015). Lab-assay for estimating methane emissions from deep-pit swine manure storages. Journal of Environmental Management, 159, 18-26.

American Water Works Association. (2017). Standard Methods for the Examination of Water and Wastewater. American Water Works Association.

ASABE. (2019). Manure Production and Characteristics (ASAE D384.2). ASABE.

EPA. (2024). Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2022 (No. EPA 430-R-24-004). U.S. Environmental Protection Agency. https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-andsinks-1990-2022

Wilson, M., Brimmer, R., Floren, J., Gunderson, L., Hicks, K., Hoerner, T., Lessl, J., Meinen, R. J., Miller, R. O., Mowrer, J., Porter, J., Spargo, J. T., Thayer, B., & Vocasek, F. (2022). Recommended Methods Manure Analysis (M. Wilson & S. Cortus, Eds.; 2nd ed.). University of Minnesota Libraries Publishing.

Acknowledgements

We are grateful to the farms that participated in this research for providing samples and for sharing their observations with us. We are also grateful to Kevin Bourgeault, Seth Heitman, Sabrina Mueller, and Jacob Olson for contributing to sampling and laboratory analysis.

This research is supported by through USDA NIFA Award 2023-68008-39859, and the Minnesota Rapid Agricultural Response Fund.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date. 

 

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Laboratory estimation of methane emission rates from Midwest dairy manure samples representing common manure types and storage conditions

Purpose

Methane (CH4) emissions from manure storage are a substantial contributor to the cradle-to-farmgate climate footprint for many dairy farms, especially for farms storing manure as liquid or slurry (Rotz et al., 2021). Dairy systems handle, treat, and store manure in various ways. In combination with environmental conditions, these differences in manure-related structures and processes potentially cause substantial farm-to-farm variability in CH4 production and intensity. However, few methods are available to estimate CH4 emissions specific to a manure storage or farm system.

To enable estimation of CH4 emission rate per unit of manure (methane emission rate, MER), research by Andersen et al. (2015) tested a laboratory assay on swine manure from deep pits. These authors showed that MER was related to manure chemical composition and varied across the year, with the highest values recorded in late fall. Our research aimed to build on Andersen et al. (2015) by testing dairy rather than swine manure to 1) compare MER across a variety of manure types, storage types, and typical storage durations, 2) examine seasonal differences in MER, and 3) quantify farm-to-farm and storage-to-storage variation in MER. Ultimately, we expected to illustrate how the MER laboratory assay could be used in estimating farm-specific CH4 emission rates from dairy manure storages.

What Did We Do?

We partnered with 27 dairies in the U.S. Upper Midwest with liquid and slurry manure storages. At approximately 2–4-month intervals throughout 2024, we collected composite samples (n = 208) representing various manure types, typical storage durations, and storage types. Most samples were whole manure (n = 165, 79%) or liquid separated manure (n = 34, 16%), with remaining samples representing flush water and digestate. Samples represented areas where manure was stored for short durations (≤1 mo.; n = 120, 58%) and long durations (>1 mo.; n = 88, 42%). Most long-term storage was unroofed, and most short-term storage was roofed. Samples represented transfer pits (n = 84, 40%), unroofed basins or pits (n = 67, 32%), and below-building pits (n = 30, 14%), among other storage types. Samples were distributed evenly across seasons for most farms, except that fewer samples were collected during winter due to outdoor storages freezing over.

For the MER assay, we incubated 75.06 ± 0.02 g (mean ± standard error) of manure at 72°F in triplicate 100 mL serum bottles for 2.99 ± 0.01 days. Then, we measured gas displacement with a syringe and headspace CH4 concentration with gas chromatography (Agilent 490 Micro GC, Agilent Technologies, Inc., Santa Clara, CA). We calculated MER as the average CH4 emission (mL) at 72°F per liter of manure per day. To examine differences due to manure type, typical storage duration, storage type, and season, we fit linear mixed models to log-transformed MER, then back-transformed model-implied means and standard errors. Additionally, we examined variance components attributable to individual storages and farms in relation to the residual variance. Storage-to-storage differences explained a small amount of total variance, so the random effect of storage was removed. Significance was declared at p<0.05.

What Have We Learned?

Across samples, the MER was highly variable and right-skewed (mean = 37, median = 21, standard deviation = 45 mL CH4 L-1 d-1; Figure 1), with a small fraction of extremely high values (maximum = 236 mL CH4 L-1 d-1). In contrast with our expectations, we found no effect of manure type, typical storage duration, and storage type on MER. Season influenced MER (F [3, 183.4] = 11.3, p < 0.001), with Fall samples exhibiting a larger MER compared with other seasons (Table 1). Larger MERs in Fall samples were driven by greater gas volume and CH4 concentrations in headspace; model-implied means of both variables nearly doubled in Fall compared with other seasons. Considering that all samples were incubated at the same temperature during the MER assay, greater MER during Fall may indicate that these samples had more abundant and active methanogen populations. Additionally, differences in chemical and physical properties of manure may have enhanced substrate availability for methanogenesis in Fall samples relative to other seasons.

Table 1. Results of a laboratory assay to estimate methane emission rate from dairy manure samples (n = 208) by incubating at 72°F in serum bottles for 3 days.
Model-Implied Mean (Confidence Interval)
Variable Spring Summer Fall Winter
Volume displacement, mL 14 (3, 25) 16 (4, 27) 26 (14, 37) 13 (0, 26)
Headspace methane, % 5 (3, 10) 8 (5, 16) 14 (8, 26) 6 (3, 12)
Methane emission rate,
mL CH4 L-1 d-1		 13 (7, 25) 22 (11, 43) 41 (21, 79) 15 (7, 33)

 

Although our results illustrated that the mean MER was generally similar across categories of manure types, storage durations, and storage types, we found that between-farm differences accounted for 18% of the total variance in MER. In other words, samples from the same farm were correlated on average 0.18. This suggests that there are farm-to-farm differences in MER that were not explained by the predictors we considered as fixed effects.

Figure 1. Methane emission rates of samples (n = 208 points) showing the median and first and third quartiles (box) with whiskers 1.5 times the interquartile range.
Figure 1. Methane emission rates of samples (n = 208 points) showing the median and first and third quartiles (box) with whiskers 1.5 times the interquartile range.

Future Plans

In future work on this project, we plan to explore if between-farm differences in MER can be explained by other farm meta-data such as bedding type, manure removal frequency, storage volume, and surface area of manure. Additionally, we will explore relationships between manure chemical composition (total solids, volatile solids, total nitrogen) and MER. Similar to Andersen et al. (2015), we are examining the temperature sensitivity of methanogenesis in different sample types. In subsequent work, we may consider relating MER to other chemical constituents in manure samples related to substrate availability (e.g., fiber fractions) or fermentation end-products (e.g., volatile fatty acids).

Authors

Presenting author

MaryGrace Erickson, Postdoctoral Associate, University of Minnesota

Corresponding author

Erin Cortus, Associate Professor and Extension Engineer, University of Minnesota, ecortus@umn.edu

Additional author

Noelle Cielito Soriano, Ph.D. Candidate, University of Minnesota

Additional Information

Andersen, D. S., Van Weelden, M. B., Trabue, S. L., & Pepple, L. M. (2015). Lab-assay for estimating methane emissions from deep-pit swine manure storages. Journal of Environmental Management, 159, 18–26. https://doi.org/10.1016/j.jenvman.2015.05.003

Rotz, A., Stout, R., Leytem, A., Feyereisen, G., Waldrip, H., Thoma, G., Holly, M., Bjorneberg, D., Baker, J., Vadas, P., & Kleinman, P. (2021). Environmental assessment of United States dairy farms. Journal of Cleaner Production, 315, 128153. https://doi.org/10.1016/j.jclepro.2021.128153

Acknowledgements

We thank the farms who participated in this research for providing samples and data. Additionally, we are grateful to Kevin Bourgeault, Seth Heitman, Sabrina Mueller, and Jacob Olson for contributing to sampling and laboratory analysis. This research is supported by USDA NIFA Award 2023-68008-39859, and the Minnesota Rapid Agricultural Response Fund.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date. 

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Pilot-scale Composting System to Measure Air Emissions from Dairy Manure and other Byproducts

Purpose

The overall objectives of this research are to investigate the design, implementation, and evaluation of a pilot-scale composting system for dairy manure. This composting system was developed because of the significant quantities of dairy manure produced in Idaho and the need to improve dairy compost quality while reducing air emissions during the composting process. This composting system provides the ability to simulate on-farm composting in Idaho while measuring and regulating key composting parameters, gas emissions, and implementing changes during operation.

What Did We Do?

This pilot-scale composting system was developed by adapting a home composter to simulate a mechanically turned windrow system. The composters were modified to include aeration control, air monitoring equipment (Gasmet), and measure key composting parameters throughout the process. Ten compost reactors were built, which allowed for several combinations of treatments and multiple replications. Each reactor is connected to a plenum with the capacity to interconnect several reactors or isolate each one and regulate airflows and chamber pressure. During the initial trial, two replications of each amendment: control, biochar, pumice, wood chips, and zeolites were evaluated. A follow-up trial will repeat the two replications per treatment, for a total of four replications. Modifications of the composting system during the trial addressed challenges with moisture control, odor, temperature regulation, air velocity, and compost balling.

Figures 1 and 2 define the blocking pattern and layout of the composting system for all ten compost reactors. The blocking pattern was generated for two primary reasons: Create replications for each treatment and compensate for a temperature differential between both ends of the research space caused by the cooling method in the greenhouse.

Figure 1. Diagram of air plenum that hangs above the compost reactors. Source: Authors

Figure 2. Diagram of gasmet tubing color coded with three separate lengths of PTFE tubing to each reactor. Source: Authors

What Have We Learned?

We learned that the pilot-scale composting system can effectively simulate different types of on-farm composting methods, demonstrating its adaptability for research. During the composting trial, the aeration was regulated to simulate forced and natural airflow composting systems. The ability to continuously measure the headspace size confirmed a significant decrease in composting volume, as expected in a full sized composting system. The temperature monitoring showed we were able to reach thermophilic composting for the first two weeks of the trial and showed temperature increases at each turning event. These findings indicate that this system can be a valuable tool for developing more efficient on-farm dairy manure management practices at the pilot-scale.

Future Plans

The design and implementation of this composting system have only completed one trial run. The immediate next step is to complete another round of the compost trial. Each resulting compost mix with the corresponding amendment will be tested in a crop-testing greenhouse trial. The amount of compost, or any other products, handled by these reactors allows for further tests in the lab, at the pilot scale, or in a greenhouse.

In the short term and beyond the dairy manure trials, the reactor system will be tested for other processes, including different composting techniques and amendments. Other processes to be tested include soil amendments and their impact on air emissions, anaerobic digestion without mixing, emissions from diverse waste streams and amendment combinations, among others.

Authors

Presenting author

Anthony Scott Simerlink, Assistant Professor, Extension Educator – Power County, University of Idaho

Corresponding author

Mario E. de Haro-Martí, Professor, Extension Educator – Gooding County, University of Idaho, mdeharo@uidaho.edu

Acknowledgements

Funding for this project was provided by a USDA-NIFA Sustainable Agriculture Systems (SAS) grant #2020-69012-31871.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date. 

 

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The Role of Agriculture in Atmospheric Nitrogen Deposition: Sources, Impacts, and Management

Agriculture is the largest source of ammonia emissions and contributes to nitrogen deposition which can impact ecosystem health. This webinar introduces the topic of nitrogen deposition and provides an overview of the role of the National Atmospheric Deposition Program (NADP) in determining nitrogen deposition sources. In addition, the speakers provide an overview of a region being impacted by agriculture related nitrogen deposition and discusses agricultural management practices that may reduce ammonia emissions and nitrogen deposition. This presentation was originally broadcast on September 20, 2024. Continue reading “The Role of Agriculture in Atmospheric Nitrogen Deposition: Sources, Impacts, and Management”

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Call for Abstracts for Waste-to-Worth 2025

You are invited to participate!

The Waste to Worth Conference will be April 7-11, 2025 at the Grove Hotel in Boise, Idaho.

Waste to Worth 2025 welcomes oral, poster, panel, and workshop presentation proposals focused on applied solutions related to animal manure management and protecting the environment.

    • Submissions should align with one or more of the general areas of emphasis (see below).
    • Graduate students are encouraged to submit and participate in a poster presentation competition.

To submit an abstract, go to https://tinyurl.com/W2W2025

For more information, go to: https://wastetoworth.org or the W2W Call for Abstracts flyer.

Deadline is October 30, 2024

Areas of Emphasis

    • Circular Bioeconomy
    • Biosecurity
    • Feed & Nutrient Management
    • Manure, Soil Health & Sustainability
    • Emerging Contaminants
    • Manure Storage, Treatment, Handling & Application Systems
    • Robotics & Artificial Intelligence in Animal Production Systems
    • Value-Added Products from Agricultural Production Systems
    • Climate Impacts & Adaptation/Mitigation Measures
    • Air Quality, Emissions & Fate
    • Educational Programming & Delivery
    • Environmental Planning & Regulations in Animal Agriculture
    • Case Studies/On-Farm Experience
    • Mortality Management
    • Sustainable Animal Systems
    • New & Innovative Technology
    • Water Quality

Who attends?

    • Extension agents & specialists
    • Progressive farmers & producers
    • NRCS staff
    • Consultants & technical experts
    • Regulatory & policy advisors
    • Scientists
    • Technology providers