Practices to Reduce Methane Emissions from Livestock Manure Management

There are several common manure management practices that can reduce methane emissions. When selecting a manure management practice, one should also consider its impact on other potential greenhouse gas (GHG) emissions (such as nitrous oxide) or sinks (such as carbon sequestration). In general, liquid manure management systems lead to anaerobic conditions and increased methane production, and switching to practices that manage manure in drier, aerobic conditions reduces methane emissions. This overview does not address enteric fermentation or agricultural soils emissions or sinks. The U.S. Greenhouse Gas Inventory provides more information about agricultural emissions and sinks in the US.

Relative Methane Reductions of Manure Management Practices
(Scale based on ½ leaf = 10% methane reduction)
Manure Management Practice	Relative Methane Reductions*
Anaerobic Digestion
Daily Spread
Pasture-Based Management
Composting
Solid Storage
Manure Drying Practices
Semi-Permeable Covers, Natural or Induced Crusts
Decreased Manure Storage Time
Compost Bedded Pack Barns
Solid Separation of Manure Solids Prior to Entry into a Wet/Anaerobic Environment

*Notes:

Methane emissions and reductions calculated based on the methodologies provided in the Inventory of U.S. Greenhouse Gas Emissions and Sinks, the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, and the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.
Methane reductions are estimated based on converting from an uncovered anaerobic lagoon in a dry temperate climate. If converting from other scenarios or practices, relative emission reductions would differ.
Anaerobic digestion reductions assume energy production and include indirect reductions resulting from the avoided use of fossil fuels.

Anaerobic Digestion

Description	Anaerobic digestion is a process through which microorganisms break down organic matter—such as animal manure, wastewater biosolids, and food wastes—in the absence of oxygen. Anaerobic digestion with biogas flaring or utilization reduces overall methane emissions and provides many benefits. Common designs include covered anaerobic lagoons, plug flow digesters, and complete mix digesters.
Best Use Cases	Most common on swine and dairy operations that manage manure as a liquid or slurry and collect at a single location. Suitable for all climates, depending on the anaerobic digestion type selected. Suitable for large and small facilities (although there are economies of scale favoring large operations).
System Requirements	Manure should be managed as a liquid or slurry and should not contain any materials that may inhibit the digester such as sand. Pretreatment may be required to reduce the size of the feedstock and remove contaminants. Needs infrastructure to process, transport, and destroy or use biogas and digestate products.
Challenges/Limitations	Requires staffing for regular maintenance and management. May be subject to permitting requirements. High initial expenses.
Potential GHG Emissions Reductions	Methane emissions are directly reduced from anaerobic digester systems used for manure management. In addition, when biogas is used for energy, methane emissions are indirectly reduced from avoided fossil fuel use. Anaerobic digestion systems emit less methane compared to uncovered anaerobic lagoons because the methane emissions are captured and destroyed or utilized. Nitrous oxide emissions may slightly increase. Net GHG emissions are expected to decrease.
Cost Considerations	High capital and operating costs can be offset by the production of electricity, heat, and/or transportation fuel, the injection of biogas into existing natural gas pipelines, and the development of byproducts such as fertilizer or bedding.
More Information	AgSTAR Project Development Handbook, U.S. EPA.

Daily Spread

Description	In a daily spread management practice, manure is removed from a barn and is applied to cropland or pasture daily.
Best Use Cases	Suitable for smaller farms. Suitable for warmer climates as this practice is done daily, regardless of soil condition, weather, or time of year. Manure should not be spread near waterbodies or on snow to prevent runoff.
System Requirements	Equipment to collect and land apply manure daily. Avoid spreading manure near wells, springs, sinkholes, terrace tile inlets, wetlands, or on slopes adjacent to streams, rivers, or lakes. Adequate land area to apply manure is needed.
Challenges/Limitations	Best suited for smaller farms that have time and resources to spread manure daily. There can be concerns for the area's water quality when spreading manure during precipitation events or in colder climates due to runoff from frozen ground. Daily spread can result in over application of nutrients if there is not adequate land to apply manure.
Potential GHG Emissions Reductions	Methane emissions are expected to decrease when converting from an uncovered anaerobic lagoon or liquid/slurry systems. This practice produces less methane emissions than an uncovered anaerobic lagoon because the manure is applied daily and is not stored for an extended time in anaerobic conditions. Net GHG emissions are expected to decrease.
Cost Considerations	There are daily labor and equipment costs associated with this management practice.
More Information	Storing Manure on Small Horse and Livestock Farms, Rutgers University. Manure timing, University of Minnesota Extension. Land Application Considerations for Animal Manure, University of Missouri Extension. Building Soils for Better Crops – Chapter 12: Integrating Crops and Livestock, Sustainable Agriculture Research and Education.

Pasture-Based Management

Description	A pasture-based management system consists of keeping animals on fenced pasture. Animals are rotated between grazing areas to improve the health of the pasture and to spread manure. Manure is left as-is to return nutrients and carbon to the land.
Best Use Cases	Best suited for ruminants, such as grazing cattle, which can rely on grasses as their main feed source. Suitable where forage is available year-round and animal confinement is not necessary for protection from the weather. In colder climates, feed would need to be supplemented when forage is not available, and confinement would be needed for protection from the weather.
System Requirements	Sufficient fenced acreage per animal to support the animals' nutritional needs, allow for rotated pastures, and manage the nutrient load of the manure. Supplemental manure management for milking areas in dairy operations and for areas of animal confinement.
Challenges/Limitations	May require acquisition of land suitable for pasture. Labor and investment required to: Develop a grazing management plan. Perform pasture maintenance such as the spreading of nutrients and weed management. Provide water and any supplemental nutrients. Manage temporary fencing needed for pasture management. Weather challenges must be addressed, such as animal confinement in the colder months and water and shade availability in paddocks. Grazing and rotating animals near streams or waterbodies will require added fencing to protect water quality.
Potential GHG Emissions Reductions	Methane emissions from manure management are expected to decrease when converting to pasture from solid storage, anaerobic lagoon, or liquid/slurry manure management systems. This practice produces less methane emissions from manure management than an uncovered anaerobic lagoon because the manure is not stored in anaerobic conditions. Carbon can be sequestered in the soil with this practice and nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	Fencing and the purchase of land may be necessary. Labor and capital investment in pasture maintenance should be considered as well. A supplemental feed budget is necessary when the nutrient needs of animals cannot be met solely by grazing.
More Information	Grazing and pasture management best practices for cattle, University of Minnesota Extension. Evaluating greenhouse gas emissions from dairy manure management practices using survey data and lifecycle tools, Journal of Cleaner Production.

Composting

Description	Composting is the aerobic decomposition of manure or other organic material by microorganisms in a managed system. Composting requires air, moisture, and high-nitrogen and high-carbon organic material. Typically, manure and bedding or wood chips are the high-nitrogen and high-carbon materials, respectively. Turning is required to aerate and evenly compost the pile. The process generally takes several weeks to months depending on the level of turning/aeration management. There are various composting methods: Composting in vessel (composting in an enclosed vessel with continuous mixing providing aeration). Composting in aerated static pile (composting in piles with forced aeration but no mixing). Composting in intensive windrows (with regular turning for mixing and aeration). Composting in passive windrows (with infrequent turning for mixing and aeration).
Best Use Cases	More suitable for manure from dairy, horses, goats, poultry litter, and beef cows with a moisture content of 40-65%. Some manure may need to be dried or separated to increase the solids content before composting. Typically, better suited for warm climates, but composting within buildings or with covers can make the practice suitable for colder weather climates. Suitable for operations that use liquid storage systems with solid separation, where liquids are stored, and solids are composted. Ideal for situations where nutrients need to be exported from the farm since composting reduces volume and weight of the manure, reducing shipping cost.
System Requirements	Space requirements are dependent on each unique system's characteristics. System may require the addition of water to prevent the compost from becoming too dry. Runoff should be prevented from entering open composting areas. Equipment to monitor temperature, as well as equipment for aeration or turning is needed. Proper ratios of carbon to nitrogen must be maintained.
Challenges/Limitations	Wet or more concentrated manure, such as that from swine or dairy farms, needs to be dried or mixed with material compost properly. Additional water may be required to maintain the rate of the composting process. Constant management is required. Compost and weather conditions, like temperature and precipitation, need to be monitored to maintain the rate of decomposition and determine how often to turn windrows. Compost must be managed properly to prevent odors, ammonia emissions, and water quality issues associated with stormwater runoff from the composting area.
Potential GHG Emissions Reductions	Methane emissions are expected to decrease when converting from an uncovered anaerobic lagoon or liquid/slurry system. This practice produces less methane emissions than an uncovered anaerobic lagoon because the manure is stored in aerobic conditions. Nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	The initial infrastructure, materials, and equipment are the main components of the cost, but regular maintenance is required. The costs may be mitigated by the sale of compost, but the market for compost needs to be considered since demand for compost is often higher near urban areas.
More Information	Large-Scale Organic Materials Composting, North Carolina State University Extension. The FARM Environmental Stewardship Continuous Improvement Reference Manual – Chapter 5: Reducing Emissions through Manure Management, National Dairy Farm Program.

Solid Storage

Description	Solid storage is the storage of manure, typically for a period of several months, either in an open area with unconfined piles or stacks or in a dedicated storage facility where the manure is confined within the walls of the facility. Solid storage can be part of a manure management system with solid-liquid separation or manure drying but combining these practices is not required.
Best Use Cases	Suitable for any animal type. Typical in colder climates; covered facilities can aid with snow and rainfall events. Where rainfall/runoff is an issue, consider using a roofed manure storage facility or vegetated filter strips to treat runoff water.
System Requirements	Sufficient storage space is needed. Size is dependent on each unique system's characteristics. An impermeable surface may be needed in humid climates. Surrounding land needs to be well-drained with vegetated filter strips around the drainage area. Equipment for gathering and moving manure is required. Concrete or other soil armoring techniques may be needed where equipment is used frequently, depending on the soil type. Pest and odor control systems are required. USDA NRCS standards specify that dedicated storage facilities should have walls surrounding at least three sides.
Challenges/Limitations	Pests and odor are concerns with this practice. Manure needs to be regularly gathered and managed to ensure easy and efficient transport. Space may be a concern due to the amount of manure that can accumulate. It can be time consuming to gather and manage the manure. There are often local and state laws regarding construction and management of manure storage facilities. Manure should be covered to better manage moisture and avoid anaerobic conditions in the stored manure.
Potential GHG Emissions Reductions	Methane emissions are expected to decrease when considering a baseline of an uncovered anaerobic lagoon because this practice has less wet, anaerobic conditions. Nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	The costs associated with storing manure in piles or stacks is low, however the costs of constructing dedicated storage facilities are higher.
More Information	Solid Manure Collection and Handling Systems, Livestock and Poultry Environmental Learning Community. Storing Manure on Small Horse and Livestock Farms, Rutgers University.

Manure Drying Practices

Description	Manure drying involves any of a variety of methods to reduce the liquid content of manure to achieve a solids content of 13 percent or more. Manure drying is commonly used so that the manure can be stored or transported more easily. Drying practices include: Open solar drying– manure is dried on a paved or unpaved lot with direct sun exposure and accumulating manure may be removed periodically. Closed solar drying – manure is dried with the use of an enclosed solar dryer, which increases drying efficiency, blocks precipitation, and contains runoff. Forced evaporation with powered dryers – manure is dried with dryers that utilize natural gas or other fuels. Drying with existing heat sources–using residual heat from barns to dry manure using fans that circulate warm air, draw out moisture through thermal convection, and reduce ammonia emissions.
Best Use Cases	Commonly used at poultry operations but can be used with other animals. Suitable farms that use manure scraping or a flush and solid separation system that produce drier manure. Open solar drying: Suitable for hot, dry climates. Suitable for smaller operations that have space available for drying. Closed solar drying: Can be done year-round in any climate because manure is dried indoors. Suitable for smaller operations that have the space available for drying. Forced evaporation: Can be done year-round in any climate because manure is dried indoors. Suitable for operations with access to natural gas. Drying with existing heat sources: Suitable for any climate; utilizes residual heat in the winter and ambient air in the summer. Best suited for poultry houses, which have residual heat.
System Requirements	Equipment and infrastructure are dependent on the manure drying technique: Open solar drying requires the installation of a drying pad; size is dependent on the farm system. Closed solar drying requires the development of a specialized building. Systems utilizing alternative heat sources require specialized ventilation systems and drying equipment.
Challenges/Limitations	Solar drying has several challenges including large space and labor requirements, variable drying rates, and the risk of microbial and insect contamination. Alternative heat source factors, such as temperature and velocity, and the volume of the manure must be optimized to decrease drying time and ammonia emissions. The drying process must be regularly monitored so dry manure can be removed and fresh manure can be added to the system. There may be local, state, or regional permitting requirements.
Potential GHG Emissions Reductions	This practice can reduce methane emissions as compared to an uncovered anaerobic lagoon because the manure is dried, thus decreasing the amount of total solids going to a lagoon that would be held in anaerobic conditions. Nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	Infrastructure costs for space requirements or specialized buildings vary based on the different manure drying techniques. Additional equipment is necessary to optimize drying time and to spread and collect manure. There are also associated labor costs.
More Information	An Effective Passive Solar Dryer for Thin Layer Drying of Poultry Manure, American Journal of Engineering and Applied Sciences.

Semi-Permeable Covers, Natural or Induced Crusts

Description	Semi-permeable covers or natural or induced crusts enclose open manure storage. These covers can reduce methane, ammonia, and odor. Geo-textile, straw, wood chips, and induced or natural crusts can be used in this practice. Induced or natural crusts are a result of biological and physical activity that occurs in the manure.
Best Use Cases	Best suited for dairy cattle operations. Suitable for all climates. Straw covers are typically used for small, accessible manure storage areas.
System Requirements	Installation of a cover or generation of a crust barrier over outdoor liquid manure storage or treatment areas (such as an anaerobic lagoon). Natural or induced crusts are more likely to form with the following conditions: heavy organic bedding use, high-forage diets, limited wash water, shallow storage structures, and low wind disturbance. The application of straw covers requires the use of a straw chopper or blower.
Challenges/Limitations	Covers require maintenance to: Prevent leaks in the cover. Repair tears and remove debris. Straw must be broken up prior to covering the lagoon, and straw covers only last up to 6 months.
Potential GHG Emissions Reductions	Semi-permeable covers and natural or induced crusts reduce the release of methane emissions. Nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	Maintenance, equipment, and materials costs are dependent on the type of cover used.
More Information	The FARM Environmental Stewardship Continuous Improvement Reference Manual – Chapter 5: Reducing Emissions through Manure Management, National Dairy Farm Program. Manure Storages- Permeable Covers Overview, Iowa State University.

Decreased Manure Storage Time

Description	Decreasing manure storage time involves limiting the amount of time manure is stored by processing or transporting it out of a storage facility, such as a slatted floor pit storage, at a reduced storage interval. Reducing the time in storage reduces the time that the stored material is in anaerobic conditions. One option to decrease storage time is to apply the manure to the land consistently during periods of good weather and soil conditions. Daily spreading of manure will have the greatest reduction in methane production but reducing storage time from months to weeks can also have a significant effect.
Best Use Cases	Suitable for all animal types. Suitable for warmer climates that have favorable land application conditions. Farms with enough land area and flexibility to land apply the manure even during less than favorable weather conditions.
System Requirements	Sufficient appropriate land to apply manure (e.g., cropland, grasslands, woodlands). May require alteration of the farm's nutrient management plan. Land application equipment.
Challenges/Limitations	It may be difficult to schedule frequent land applications for some crop rotations and special equipment may be required. Timing of land application will need to be managed to avoid application to frozen or wet ground, which could cause runoff and water quality issues. Increased land application requires more dedicated labor.
Potential GHG Emissions Reductions	Shorter storage times provide less time for the manure to break down and produce methane emissions. Nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	Equipment changes for more frequent manure land application may be needed. There may also be increased labor costs for this technique.
More Information	Manure Storage: Small Scale Solutions for Your Farm, USDA NRCS.

Compost Bedded Pack Barns

Description	Compost bedded pack barns are a housing system that include a deep bedding - such wood shavings, sawdust, or other adsorbent bedding materials. Animals can freely roam on the pack and through walkways to access the feeding area. The pack is aerated, usually twice daily, mixing the manure into the pack, providing the animals with a fresh surface. The bedding can be removed and land applied or composted further. This system is generally an alternative to tie or free stalls for dairy cows.
Best Use Cases	Primarily used with dairy cows; more rarely used with swine and beef cattle. Suitable for northern climates, although more heat and bedding are required in colder temperatures. This practice is not recommended for southern climates, due to the increase in pathogen growth which can lead to higher incidence of inflammatory compounds in milk (a decrease in milk quality) and infection.
System Requirements	Requires at least 100 square feet of resting space per cow (85 square feet for Jerseys) and additional space for higher producing herds. A ventilated housing system with appropriately sized resting space is required. The bedded pack requires aeration (usually twice daily) to manage moisture, typically done with a cultivator, tines, or a rotary tiller during milking.
Challenges/Limitations	Sufficient space should be available for each cow to ensure there is enough dry material to properly handle manure, urine, and pack moisture levels. Requires proper management, including: Tilling the pack when animals are not in the barn to prevent dust exposure for animals. Maintaining proper ventilation needs. Distributing heat and light evenly in the barn to ensure that the animals do not overcrowd one area of the pack. If poorly managed, the bedded pack can become a favorable environment for pathogens, which can negatively affect the health of the animals.
Potential GHG Emissions Reductions	Methane emissions are expected to decrease when converting from an uncovered anaerobic lagoon, remain unchanged when converting from a liquid/slurry system, and increase when converting from composting, solid storage, or daily spread. This practice produces less methane emissions than an uncovered anaerobic lagoon because the pack is aerated to reduce anaerobic conditions. Nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	A new barn or modification is often required to ensure there is adequate ventilation and space for each animal. Additionally, bedding is necessary to maintain moisture levels. There will be increased labor costs for the management and maintenance of the pack. The cost of a compost bedded pack barn can be less expensive than a traditional liquid storage.
More Information	Compost-bedded pack barns for dairy cows, University of Minnesota Extension. Compost Bedded Pack Barn Design: Features and Management Considerations (pdf), University College of Agriculture. Winter Management of Dairy Compost Bedded Pack Barns (pdf), University of Kentucky College of Agriculture. Compost-bedded pack barns for dairy cows, Journal of Dairy Science. Composted Bedding Pack Barns Video, Farm & Food Care.

Solid Separation of Manure Solids Prior to Entry into a Wet/Anaerobic Environment

Description	Solid separation techniques generally fall into two main categories: those that separate solid particles from water based on density, and those that separate solids based on particle size. Solid separation technologies include: Screw Press Centrifuge Roller Drum Belt Press/Screen Weeping Wall Stationary Screen Vibrating Screen Solid-liquid separation can be used to achieve objectives such as excluding solids from storage structures or lagoons, improving pumping characteristics, reducing organic loading on a treatment lagoon, and treating runoff from outdoor feedlots.
Best Use Cases	Commonly used for dairy cattle and swine but can be used for beef cattle and poultry if the manure is handled as a liquid or slurry or is combined with other liquids. Where a decreased lagoon organic loading is desired because separating solids reduces lagoon organic loading. Separating solids can also allow for hauling of manure to fields further away, which can improve nutrient management.
System Requirements	Manure must be handled as either a liquid or a slurry. If sand bedding is utilized, the sand must be removed prior to solid-liquid separation. The separation method is dependent on the characteristics of the manure and the climate. In colder climates, separation may need to be done in a building.
Challenges/Limitations	Capital and operational costs associated with solid-liquid separation may not be feasible for small operations. Sand bedding can cause issues with the separation equipment.
Potential GHG Emissions Reductions	This practice results in reduced manure in liquid storage, leading to reduced methane emissions. The portion of manure that is moved from liquid storage to solid storage produces fewer methane emissions because solid storage is not as anaerobic as liquid storage. Nitrous oxide emissions may increase. Lifecycle analysis may be necessary to estimate net GHG emission reductions.
Cost Considerations	Each type of separation method has equipment, labor, and space requirements. Energy requirements can be high and can increase costs. Cost savings can occur by replacing straw or other materials used for cattle bedding with the removed solids.
More Information	Environmental Engineering National Engineering Handbook – Chapter 4: Solid-Liquid Separation Alternatives for Manure Handling and Treatment (pdf), USDA NRCS. Solid-Liquid Separation of Manure and Effects on Greenhouse Gas and Ammonia Emissions, University of Wisconsin Extension. The FARM Environmental Stewardship Continuous Improvement Reference Manual – Chapter 5: Reducing Emissions through Manure Management, National Dairy Farm Program.