Perceptions of Agricultural Stakeholders on Manure Use, Benefits, and Barriers

Purpose

Nutrient recycling is fundamental to agricultural systems (Spiegal et al., 2020). Integration of animal and crop production represents an example of the application of a circular economy to manage nitrogen (N), phosphorus (P), and other nutrients (Figure 1) important to crop and livestock production. An integrated system recycles these critical nutrients from animal feed to manure to soils and back to animal feed. Nutrient additions to the farm, like animals, feed, and fertilizer (input arrow), are necessary to offset the nutrients leaving the farm in animal protein products (output arrow), as well as other nutrient losses in the system (Cela et al., 2014). The efficiency of this nutrient recycling process has both environmental and economic sustainability implications.

Figure 1. Recycling of nutrients is critical to an environmentally sound agricultural “circular economy”.

For many regions of the United States, such as the Corn Belt, animal agriculture remains in relatively close proximity to sufficient crop production to allow agronomic recycling of nitrogen and phosphorus (Gollehon et al., 2001, 2016). However, the sources of manure nutrients (livestock and poultry operations) and the consumers of nutrients (cropland) are often managed as independent businesses. In other regions, separation of feed and animal production by distance and business boundaries creates significant challenges for agronomic nutrient recycling (Spiegal et al., 2020).

The willingness of crop farmers to accept manure as part of their fertility program is dependent upon their perceptions of the benefits and challenges associated with using manure. Likewise, behaviors among farmers and agricultural advisors of information-seeking – “purposive acquisition of information from selected information carriers” (Johnson 1996) – must be considered as a precursor to content delivery. Thus, in early 2020, a faculty team from University of Nebraska, University of Minnesota, and Iowa State University collaborated to implement a survey of farmers and their advisors to guide multi-state outreach programming by identifying:
-Challenges that regularly prevent manure’s use in crop production and
-Perceptions of manure’s benefits that may encourage manure transfers from livestock farmers to crop producers.

What Did We Do

A draft survey was tested with three groups (a stakeholder advisory group, the national Livestock and Poultry Environmental Learning Community, and the Nebraska Animal Manure Management team) leading to the final product. The survey was delivered electronically through QualtricsXM survey application tool using a University of Nebraska-Lincoln licensed product. The survey included questions for the participants on the following subjects of interest:
1. Participant’s role in manure decision making.
2. Perceptions and knowledge of manure’s benefits. Participants were asked to rate the degree to which they considered manure to be harmful or beneficial for crop fertility, soil physical characteristics, soil biological characteristics, crop yields, and environmental quality.
3. Perceptions and knowledge of manure’s challenges. Participants were presented with a list of potential barriers which might prevent manure use in crop fertility programs and asked to identify which factors were barriers for their operations, or for their advisees.
4. The types of supporting resources which would be of most value for the participants’ decision making or advising on manure benefits and barriers.

Surveyed Participants
Responses were received from 793 individuals across the U.S. and Canada. The results are heavily weighted towards participants from the Corn Belt and the High Plains regions of the U.S. (44% and 23% of respondents, respectively). Survey participants were 87% male and 13% female. Participants’ experience were reported as 29% with less than 10 years, 22% with 11 to 20 years, and 49% with 21 years or more. Participants self-identified as a crop farmer (13%), animal feeding operation (AFO) (7%), professional advisor for crop fertility or manure management decisions (60%), or some combination of these three roles (20%). Crop farmers indicated that they were an annual user of manure (73%), user of manure within the past 3 years (9%), or user of manure within past 4 to 6 years (9%). Only 10% were not users of manure. Those identifying as advisors suggested that manure management is a primary focus of crop fertility advising (20%), frequent part of crop fertility advising (39%), or an occasional part of a crop fertility advising (36%). Only 4% of advisor responses indicated they did not include manure in their advising.

Figure 1. Region of US and Canada represented by survey participants (N= 793).

A series of five questions were presented to identify real or perceived challenges among respondents that represent potential barriers to using manure in crop fertility programs. Lists of agronomic, economic, neighbor or rural community, regulatory, and logistical challenges were presented based on outcomes of the project team’s advisory group discussions and reviews of previous surveys (Battel and Krueger, 2005; Case et al., 2017; Herrero et al., 2018; Poe et al., 2001). Lastly, respondents were asked to identify the types of supporting resources preferred for information-seeking on manure use in cropping systems.

What Have We Learned

Perceptions and Knowledge of Manure Benefits. Both private sector advisors and crop farmers shared similar positive impressions of manure’s benefits for crop fertility, yield, and soil characteristics while being less positive regarding their impressions of how manure impacts environmental quality. Crop farmers and private sector advisors recognize the complementary role of manure and fertilizer in a fertility program at 74% and 76% frequency, and at slightly higher rates than all survey responses (71%). The complementary role of manure and fertilizer was also similar across regions (Corn Belt – 70%; High Plains-69%; all other regions – 74%).

Figure 2. Perspectives of manure’s beneficial versus harmful impacts on five crop production and natural resource topics as identified by primary decision makers in crop fertility programs.

The only audience factors that significantly (p<0.05) influenced participant attitudes toward manure benefits were that participants living in the corn belt were less likely to describe manure as beneficial or slightly beneficial for environmental quality (30%, compared to 46% for high plains, and 35% for all other regions). Similarly, we found that private sector advisors were significantly (p<0.05) less likely to describe manure as beneficial to environmental quality (27%, compared with 58%, 53%, and 30% for livestock producers, crop producers, or public sector advisors respectively). No statistical differences were observed for an influence of audience factors on attitudes towards manure benefits to any of the other characteristics of cropping system benefits (crop yield, soil physical properties, soil biological properties, and crop fertility). However, across all audience sectors participants were unlikely to indicate that they thought manure could be beneficial or slightly beneficial for environmental quality (Figure 2). This data suggests that respondents do not associate improved soil physical and biological characteristics with reduced risk for nutrient transport via runoff, erosion, and leaching. Manure and inorganic fertilizer were perceived as complementary to each other by 71% of respondents, while only 17% believed these two products compete.

Figure 2. Proportion of total respondents who described manure as beneficial or slightly beneficial for different categories of cropping system characteristics. (n=793)

Barriers to Manure Use. As with perceptions of benefits of manure use, audience factors had little effect on the perceived barriers to manure use. There was an observed tendency for more advisors to include most factors as barriers to manure use; however, this tendency was only significant (p<0.05) for six potential barriers: compaction, cost of manure transportation, odors, risks posed by manure application to food crops, accessibility of custom applicators, and use of public roads (Table 1). The overall ranking of barriers to manure use can be found in Table 2. Cost of transportation (68%), odor (58%), timeliness of nutrient availability (55%), concerns related to the field conditions for manure application (50%), and access to labor for manure application (48%) were most frequently indicated as barriers for manure use. Interestingly, several of these factors correspond to those where a difference in the level of concern was observed between advisors and producers (Table 1). However, when considering barrier ranking by agronomic role, 4 of the top 5 barriers are similar between farmers and advisors (cost of transportation, odor, timeliness, and labor availability). Farmers rate concerns with weed seeds as a top 5 barrier, while advisors do not, leaving concerns with field conditions for application as the 6th most selected by crop farmers. This similarity of ranking, even where statistical differences exist, indicates that there is agreement on what are the most significant barriers, but some difference in the perceived seriousness or scale of the barrier. In general, crop farmers less frequently indicated factors as barriers to manure use than did advisors.

Table 1: The frequency survey responses identified selected barriers for manure use. Letters indicated statistical differences in how participants with different roles in agronomic decisions perceived barriers of interest at the alpha = 0.05 level.

Comparison by Role in Agronomic Decisions Animal Feeding Operator (n=66) Crop Farmer (n=120) Private Sector Advisor (n=311) Public Sector Advisors (n=196)
Compaction from application 36%a 41%a 59%b 40%a
Cost of manure application 55%a 67%ab 84%bc 85%c
Odors an air quality impairment 44%a 56%ab 75%bc 79%c
Manure application to food crop 15%ab 13%a 20%bc 22%c
Accessibility of custom applicators 20%a 19%ab 40%b 3%ab
Use of or crossing of public roads 15%a 11%a 21%b 13%a

 

Table 2: The frequency all survey responses identified specific factors as barriers for manure use (n=793)

Potential Barrier % Who perceived as a barrier Potential Barrier % Who perceived as a barrier Potential barrier % Who perceived as a barrier
Transport 68% Water Quality 35% $ of Manure 25%
Odor 58% Interference with Reduced Tillage 34% Accessibility 25%
Timeliness 55% Neighbor Concerns 34% Legal Issues 25%
Field Conditions 50% Equipment $ 34% Flies 20%
Labor 48% Regulation $ 32% Interference with Specialty Crops 19%
Low or Inaccessible Nutrients 47% Traffic 31% Risks to Food Crop 15%
Low or Inaccessible Nutrients 47% Traffic 31% Risks to Food Crop 15%
Compaction 44% Planning & Zoning 31% Road Access 14%
Imbalanced Nutrients 44% Harm to Local Infrastructure 28% Foreign Materials 9%
Uniformity 38% Stockpiles 28% Reduced Yield 5%
Setbacks 37% Presence of Applicators 27% Harmful to Soil 3%
Weed Seeds 37% Pollution 27%

Preferred Sources of Educational Materials. Among three broad groups of respondents (farmers, advisors, and educators), all identified their peers as an important source of information. Brief factsheets or news articles are identified by educators as their top resource they would use (81% of educator responses and 65% of advisor responses). Recommended research articles also ranked high among all three groups. At this point in time, social media (short videos, podcasts, and Twitter and Facebook) is a preferred resource for a smaller portion of these audiences (26% or farmers, 15% of advisors, and 47% by educators).

 

Table 3. Most valued resources for agronomic decision making

Resource Type Farmer (n=197) Advisor (n=438) Educator (n=95)
Recommended research articles 49% 53% 55%
Brief fact sheet or news articles summarizing current science 52% 65% 81%
Decision support tool 34% 39% 43%
Short videos or podcasts summarizing current science 20% 12% 36%
Scripted visuals and text for your use on Twitter, Facebook, other 6% 3% 11%
Network of farmers (or advisors or educators) with whom you interact and share experiences 62% 61% 62%
Scripted PowerPoint presentation for use in educational programs 38%

Future Plans

The intent of this survey was to help our project team and others better understand the characteristics of animal manures that are considered beneficial and barriers to future manure use. Recognition of these benefits and hurdles will be critical as the need to transfer manure nutrients from existing animal feeding operations to crop farms, many with limited previous history of using manure, expands. Matching educational and technical services to the perceptions that impede manure transfer will be necessary.

Future outreach programming should be designed to:

    • Continue to build general awareness of the agronomic and yield benefits of manure.
    • Focus on assisting AFO managers and advisors with communication of specific messages such as 1) desirable rates/plans to best meet crop N and P needs, 2) field-by-field estimation of manure’s fertilizer replacement value and nutrients contributing the greatest value, and 3) complementary manure and fertilizer recommendations for optimum yields.
    • Focus on connecting improved soil health with improved water quality.
    • Help farmers articulate among themselves and to their rural communities the water quality benefits of organic fertilizers when applied to meet agronomic needs of the crop.
    • Challenges associated with manure that frequently become barriers to manure use should be addressed through research and outreach. Specifically, the authors wish to suggest that four challenges are commonly regarded as significant barriers to manure use and require focus to overcome:
      1. Transportation Costs: Businesses providing manure hauling and land application services will be important when transferring manure to fields more distant from manure sources, and educational experiences addressing the current costs of transporting manure and the comparative economic benefit achieved by individual fields will be important.
      2. Odor: A farmers’ desire to be a good neighbor is counter to their willingness to create odors for their neighbors. Farmer and advisor education and planning for reducing odor risks is critical. Technology options to forecast, assess, and address potential nuisance odors may help alleviate odor concerns resulting from manure application.
      3. Logistical Barriers: Three logistical issues ranking highest include 1) timeliness of manure application; 2) time/labor availability; and 3) field conditions restricting manure application. Business services for transporting and land applying manure as well as manure brokering services can address many logistical challenges. Alternative application time windows, such as side dressing a crop with manure, will also be valuable.
      4. Agronomic Issues: Manure application comes with a history of agronomic concerns such as compaction, poor uniformity, and potential for weed seed and herbicide resistance concerns. Many issues are likely to be regionally and manure source specific, thus the need to adapt agronomic education to local needs. Education and business services that encourage technologies such as precision manure application and related technologies, designer manures, and manure treatment may have value based upon regional needs. A 4Rs strategy (right rate, source, time, and place) for manure, similar to what is being promoted in the fertilizer industry, may be beneficial.

Authors

Amy Millmier Schmidt, Associate Professor, University of Nebraska-Lincoln
aschmidt@unl.edu

Additional Authors

-Mara Zelt, Schmidt Lab Project Director, University of Nebraska-Lincoln;
-Daniel Andersen, Associate Professor, Iowa State University;
-Erin Cortus, Associate Professor, University of Minnesota;
-Richard Koelsch, Emeritus Professor, University of Nebraska-Lincoln;
-Leslie Johnson, University of Nebraska-Lincoln;
-Siok A. Siek, Undergraduate Student, University of Nebraska-Lincoln; and
-Melissa Wilson, Assistant Professor, University of Minnesota

Acknowledgements

Funding for this project was provided by the North Central Region Sustainable Agriculture Research and Education program. Key partners in survey deployment were the American Agronomy Society Certified Crop Advisor Program, the Fertilizer Institute and Manure Manager magazine.

 

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. 2022. Title of presentation. Waste to Worth. Oregon, OH. April 18-22, 2022. URL of this page. Accessed on: today’s date.

Merits of Manure Content Library

Purpose

The right amount of animal manure in the right location can benefit crops, soil, and water resources.  However, too much manure or manure in the wrong place is an environmental concern.  A recent survey of attitudes from farmers and their advisors on the benefits and barriers for manure use indicates that there is widespread knowledge of manure value for cropping systems, but logistical and community barriers remain. The survey also found that all respondents rated peer-to-peer interactions as the most influential on their decision-making for these topics. Thus, more extension efforts should be focused in assisting AFO managers and advisors to communicate messages on the value of manure and strategies for overcoming barriers, among their specific networks. For example, knowledge of the relationship of manure and soil health benefits is low among some segments. Farmers and their advisors all have very low opinions and understanding of manure’s benefits to environmental quality. Helping farmers, educators, and advisors articulate among themselves and to their rural communities the water quality benefits of organic fertilizers when applied to only meet agronomic needs of the crop may need expanded investments. With these needs in mind a team from the Universities of Nebraska, Minnesota, and Iowa State, and the assistance of the North Central Region Sustainable Agricultural Research and Education program developed a library to provide educators and advisors with access to recommended resources that will assist in the discussion of manure’s benefits and challenges.

What Did We Do?

Consultation among the team identified the following categories of interest for readily accessible educational or outreach materials for manure impacts on:

    1. Soil health and soil quality
    2. Economics of production and yield
    3. Crop fertility
    4. Water quality
    5. On-farm research

And guidance to navigating barriers such as:

    1. Direct costs associated with manure use
    2. Odor and other community issues
    3. Agronomic challenges (such as imbalance nutrients)
    4. Regulations
    5. Logistical issues of application
    6. Using manure in specialty systems (such as organic production)

With the categories for materials established, the team conducted an initial survey of extant educational and outreach materials via general internet searches and review of content available through the Livestock and Poultry Environmental Learning Community. The types of content thus assembled were varied: social media content, video, summaries of research, published extension and scientific journal articles, websites, and other content such as podcasts and decision support tools. All were included since it was intended that these resources be helpful for educators, producers, or others to converse with their own networks easily and confidently on the manure topics identified. The team anticipated that users could use the library to expand their social media activity, and thus their communication networks, or to prepare more confidently to discuss manure via a local radio presentation or discussion with a county board. Or even to add an article to local print media or a blog or personal website. All items included in the library were free to repurpose (with attribution) in local outlets or personal sites.

After consultation, the library was built using Airtable ™, a platform to create low-code databases, tools, or other apps. This platform allows the team to internally build a flexible database of content which can be sorted easily into pre-set categories (for example, topics of specific seasonal relevant), and arrange content into easily perused views to improve the user experience on a platform that could be easily embedded into existing team sites, such as lpelc.org (Figure 1).

Figure 1. The user interface for the merits of manure library, several such sorted views are embedded on the LPELC website for audience exploration by topic, media type, or seasonal relevance. Within each view individual entries can be further searched or sorted to further narrow exploration.

Each entry (Figure 2) in the library has an individual entry card, which includes keywords and text descriptions to improve searchability as well as a downloadable file, or links to the resource where appropriate, and a short example of how this material could be shared in the user’s social media network (recommended twitter text). The team intended to provide library users with not only the educational content, but also the means to improve their own in-network communication on manure topics. Accordingly, when posting to social media, hashtags, mentions and links to other content help (a) reach users who are following a specific topic (e.g., #manure), (b) recognize someone related to the post (e.g., @TheManureLady) and (c) direct users to more content related to the graphic (e.g., URL to online article). For our content library, each item is accompanied by recommended text that can be copied and pasted into the post of a social media engine if desired.

Figure 2. A single-entry page for the library.

What Have We Learned?

Since its launch in 2021 the library has had 343 unique users, average time that each user spends interacting with the library is 129 seconds, a solid interaction time for a website – industry standard is 120-180 seconds. However, we do not have any measure for how time spent on the library page is transformed into use of the library content. It is evident that more work is needed to improve awareness of the tool among audiences of interest. To this end, the team decided to develop a recognizable brand for library materials which might help other potential users to find their way to the site (Figure 3).

Figure 3. Library logo.

Future Plans

Library administrators continue to look for ways to improve the library content, user experience, and awareness of the tool among potential users. An overview of content, accessibility, re-purposing, and submission of relevant material will be shared to publicize the resource, encourage utilization of available materials, and invite submissions of new content relevant to the manure management community.

Authors

Amy Schmidt, Associate Professor, University of Nebraska

Corresponding author email address

aschmidt@unl.edu

Additional authors

Leslie Johnson, Associate Extension Educator, Mara Zelt, Schmidt Lab Project Director, Amber Patterson, Schmidt Lab Media Communications Specialist, and Rick Koelsch, Professor Emeritus, University of Nebraska-Lincoln; Erin Cortus, Associate Professor, and Melissa Wilson, Assistant Professor, University of Minnesota; and Dan Andersen, Associate Professor, Iowa State University

Additional Information

The full library is accessible at https://lpelc.org/value-of-manure-library/.

Acknowledgements

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program.  NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library By Season

Winter

Spring

Summer

Fall

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library By Media Type

Media types include social media, news articles, web pages, educational publications, decision support tools, and recommended research articles.

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library By Topic Area

Topics include agronomics, economics and yield, soil health/quality, water quality, organic systems, neighbors, regulations and logistics.

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library Grid View

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library for Educators and Advisors

Purpose

Manure is a resource that comes with many benefits and challenges.  This library is designed to provide educators and advisors with access to recommended resources that will assist you in your discussion of manure’s benefits and challenges.  Educators, please feel free to share and re-purpose educational products in this library with local audiences. Advisors, the library’s resources shall provide you with decision tools and educational products for enriching your discussions with clientele and rural community residents.

How to find materials

For those seeking specific resources, materials are organized visually by topic area and type of media. For those that would rather search materials more linearly, there is a grid version available.

In all views, there is a search button in the top right corner that looks like a magnifying glass and an expansion button that looks like two outward pointing arrows to view in full screen.

By Topic Area

Preview of manure value library database sorted by topic.
    • Manure as a fertilizer
    • Manure economics
    • Soil quality/health effects
    • Water quality effects
    • Use in organic systems
    • Neighbors
    • Regulatory concerns
    • Logistics

By Media Type:

Preview of manure value library database sorted by purpose.
    • Social media
    • Short news articles and web pages
    • Educational publications
    • Decision support tools
    • Recommended research articles

 

Instructions for Re-purposing Educational Content

Our team encourages and welcomes educators and advisors re-purposing of many of the social media and web page/news article resources found in this library.  Would these resources be helpful to you for Tweeting to your followers? Assembling talking points for a local radio presentation or discussion with a county board?  Or adding an article to local print media or your blog?

Example of social media graphic to be re-purposed.
    • Twitter Posts:  A broad range of Twitter posts, graphics with an educational message and short text introduction, are included for use with your social media connections.  Please re-purpose these for your local use. We ask that you maintain the “N Extension” and “WSA” logos in your re-purposed post.  You may replace the “Manure Happens. Take Credit” caption and the “Learn more at: http:// ________”  with an appropriate recognition of your organization and/or a web page that you would like to promote.
    • Web Page/News Articles:  Many of these library products can be repurposed for a variety of local uses.  News articles and web pages may be revised to add local information with the new authors name included if the original authors continue to be listed.
    • Any Educational Products:  Any of the Library resources may be used as talking points for a local radio broadcast or community group presentations. Please recognize the original authors and resource title in your presentation.

 

Is something missing from our library?

We welcome your suggestions of resources that you have found beneficial in your educational or advisory role.  Please email any of the project team members with your suggestions or submit them via our google form for our consideration.

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University.  These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program.  NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Factors Affecting Nitrous Oxide Emissions Following Subsurface Manure Application

[Abstract] Subsurface manure application is theoretically susceptible to greater denitrification losses and nitrous oxide (N2O) emissions compared to surface application methods – primarily attributed to manure being placed in a more anaerobic environment. A review of field studies suggest N2O emissions typically range from 0.1% to 3% of total applied N from subsurface application methods, but there is considerable variation in emissions depending on pre- and post-application soil moisture conditions, readily-available carbon content in manure compared to background levels in soil, localized nitrogen form and oxygen concentration at the application site, and application depth. This paper will summarize peer-reviewed literature of field studies that quantify N2O emissions subsequent to subsurface manure application and identify the most prominent determining factors cited by authors.

Why Study Nitrous Oxide Emissions of Manure?

Ammonia abatement efficiencies of up to 90 percent have been documented with subsurface application and incorporation of animal manures compared to conventional surface application methods. While reducing ammonia emissions has positive implications for air and water quality, a portion of the nitrogen conserved may come at the expense of increased nitrous oxide emissions produced during denitrification and nitrification processes in the soil. As a greenhouse gas 300 times more potent than carbon dioxide at trapping heat, nitrous oxide has been linked to anthropogenic climate change and depletion of stratospheric ozone. Release of nitrous oxide from agriculturally-productive soils into the atmosphere also represents a loss of crop nutrients. Understanding the circumstances and manageable factors that contribute to nitrous oxide formation in soils subsequent to manure application is important for retaining crop nutrients and preventing greenhouse gas emissions.

What did we do?

A literature review was performed to investigate the factors that contribute to nitrous oxide emissions following subsurface application of animal manure to both grassland and arable land, compare results from different application techniques, and examine the conditions and circumstances that lead to nitrous oxide emissions.

What have we learned?

Several studies demonstrate significant increases in nitrous oxide emissions (from 0.1 to 3 percent) attributable to factors including increasing soil moisture content, high concentrations of readily-available carbon in manure substrate, increased nitrate concentration in soil, shallow application depth, high soil temperature, and ambient conditions during and immediately following application (table 1). Other studies show no difference in nitrous oxide emissions as compared to surface application methods. Reasons that subsurface application techniques will not necessarily result in greater nitrous oxide emissions were: 1) the length of the diffusion path from the site of denitrification to the soil surface may lead to a greater portion of denitrified nitrogen being emitted as nitrogen gas; 2) the soil moisture conditions and aeration level at the time of application may not be suitable for increased nitrous oxide production; 3) prior to manur e application, soils may already contain readily-metabolizable carbon and mineral nitrogen, thus any increase in nitrous oxide emission following application may not have a significant impact; and 4) weather events subsequent to manure application may effect soil moisture content and water-filled-pore-space, thereby affecting nitrous oxide emissions. Several studies document nitrous oxide emissions due to subsurface application methods (including manure incorporation and shallow injection) but research comparing nitrous oxide emissions from different subsurface application techniques and application depth is limited. Lack or absence of data in literature about manure chemistry, nitrogen application rates, application technique or method, as well as soil and atmospheric conditions during and after application made it more difficult to draw specific conclusions on factors affecting nitrous oxide emissions from subsurface-applied manure.

Further research is needed to determine the environmental and economic tradeoffs of implementing subsurface manure application methods for abatement of NH3 considering different future greenhouse gas emissions and market scenarios. Recent work suggests a link between denitrifier community density, organic C, and N2O emissions. Characterization of these biological mechanisms and identification of genetic markers for key enzymes should continue, particularly with respect to various subsurface manure application techniques, different manure types and N application rates, soil types, environmental conditions, and soil chemistry. Subsurface application depth plays an important role in determining the proportion of N2O to N2 emitted during denitrification; however, the number of field studies that examine the impact of application depth is limited. More research is needed to determine optimal manure application depth as influenced by soil type, soil chemistry, timing of application, and vegetative cover. Finally, future research on subsurface manure application will allow existing and future prediction models to improve estimation of annual N2O emissions at landscape scale and airshed levels. Refinement of greenhouse gas inventories, including N2O emissions from agricultural production systems, will assist agriculture producers, scientists, and policy makers in making informed decisions on greenhouse gas emission mitigation.

research articles reporting factors of Nitrous Oxide

Future Plans

Future agricultural greenhouse gas regulations and/or carbon market incentives have potential implications for agricultural producers, including the method and timing of manure application. Controlled, replicated, and well-documented research on subsurface manure application and subsequent nitrous oxide release is critical for estimating the costs and benefits of different manure application techniques.

Authors

David W. Smith, Extension Program Specialist, Texas A&M AgriLife Extension DWSmith@ag.tamu.edu

Dr. Saqib Mukhtar, Professor and Associate Department Head for Extension, Texas A&M AgriLife Extension

Additional information

The publication ‘Estimation and Attribution of Nitrous Oxide Emissions Following Subsurface Application of Animal Manure: A Review’ has been accepted for publication in Transactions of the ASABE.

Acknowledgements

Funding for this effort provided by USDA-NIFA grant No. 2011-67003-30206.

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. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

Making Sense of Treatment Technology Options for Livestock Farms

Have you ever wondered whether manure should be treated on your livestock operation? What technology will work best in your situation? This webinar discusses strategies for selecting the right technology to meet your farm’s needs and reviews some proven and emerging technologies that are showing promise for the dairy industry. This presentation was originally broadcast on February 16, 2018. More… Continue reading “Making Sense of Treatment Technology Options for Livestock Farms”