Manure Management

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Manure management produces both CH₄ and N₂O. In the IPCC methodology, manure management emissions include N₂O from the storage and treatment of livestock dung and urine before it is applied to land or used for other purposes, and CH₄ produced during the storage and treatment of manure, and from manure deposited on pasture.

Emissions from manure applied to cropland or grassland soils as an amendment are accounted for under N₂O emissions from managed soils. Emissions associated with the burning of dung for fuel are reported as energy or waste emissions (depending on whether energy is recovered).

Estimating emissions from manure management

What data are required?

Tier 1

Estimating GHG emissions from animal manure requires two types of activity data:

• Animal population data by animal subcategory (the same subcategories should be used as for enteric fermentation)
• Total amount of volatile solids (VS) excreted by animal subcategory in each type of manure management system;

The approach and activity data required to estimate emissions differ slightly between CH₄ and N₂O.

• Emissions of CH₄ = CH₄ emissions from manure management, for a defined livestock population, Gg CH₄ yr^-1
• EF_T= emission factor for the defined livestock population, kg CH₄ head^-1 yr^-1 (IPCC, 2019; Table 10.14)
• N_T = the number of head of livestock species/category T in the country
• VS_{(T, P)}= annual average VS excretion per head of species/category T, for productivity system P, when applicable in kg VS animal-1 yr-1 (IPCC, 2019; Table 10.13a calculated by Equation 10.22a)
• AWMS_{(T, S, P)} = fraction of total annual VS for each livestock species/category T that is managed in manure management system S in the country, for productivity system P, when applicable; dimensionless, default regionally specific AWMS fractions are found in IPCC, 2019; Tables 10A.6 through 10A.9)
• T = species/category of livestock
• S = manure management system
• P = high productivity system or low productivity system for use in advanced Tier 1a – omitted if using a simple Tier 1 approach

As with enteric fermentation, the only activity data required for the Tier 1 approach to estimating CH₄ emissions from manure are animal population data by animal subcategory. IPCC Tier 1 emission factors for each region assume the most common manure management system in that region.

Using the Tier 1 method, default emission factors are based on the livestock species, manure management system, and productivity system; these factors represent the range in manure volatile solids content and manure management practices used in each region.

N₂O emissions from manure (as with emissions from fertilizer) include both direct and indirect emissions. Estimating N₂O emissions from manure requires animal population data and data about manure management systems.

Tier 2

Tier 2 estimates of CH₄ from manure management require data on:

• Manure characteristics: Includes the amount of volatile solids (VS) produced in the manure and the maximum amount of methane able to be produced from that manure (B0).
• Animal waste management system characteristics (AWMS): Includes the types of systems used to manage manure and a system-specific methane conversion factor (MCF) that reflects the portion of Bo that is achieved.

To implement the Tier 2 method, one or more variables to determine the CH₄ emission factor from manure management for each country’s livestock type and manure management conditions must be improved:

• VS_T = daily volatile solid excreted for livestock category T, kg dry matter animal^-1 day^-1 (IPCC, 2019; Table 10.13a calculated by Equation 10.22a)
• 365 = basis for calculating annual VS production, days yr^-1
• B_o(T) = maximum methane producing capacity for manure produced by livestock category T, m³ CH₄ kg^-1 of VS excreted (IPCC, 2019; Table 10.16)
• 67 = conversion factor of m³ CH₄ to kilograms CH₄
• MCF_S,k = methane conversion factors for each manure management system S by climate region k, % (IPCC, 2019; Table 10.17; Annex 10.A.4)
• AWMS_T,S,k = fraction of livestock category T’s manure handled using manure management system S in climate region k (IPCC, 2019; Tables 10A.6 through 10A.9)

Volatile solids (VS) are the organic material in livestock manure, equal to the fraction of diet not consumed that is excreted as fecal material. VS excretion rates (VS_T) depend on feed intake and feed characteristics such as digestibility. Average VS excretion rates can be obtained from published literature for the country or area in question or estimated from average feed intake levels (also required for Tier 2 estimates of enteric fermentation emissions).

The Tier 2 method for N₂O from manure management uses the same equation as Tier 1 but includes country- or region-specific data for some or all of the variables, rather than Tier 1 default values (IPCC, 2019; Chapter 10 – pages 10.81-10.89).

Methods and sources of activity data

Livestock population data

Estimates of emissions from manure should be calculated using the same livestock population data as for enteric fermentation.

Manure management data

1. A fraction of manure (by weight) handled in each type of manure management system, for each animal population category, is often collected through national agricultural surveys or expert consultations.
2. Moeletsi ME, Tongwane MI. 2015. 2004 methane and nitrous oxide emissions from manure management in South Africa. Animals.
   1. Provides an example of the use of expert data to estimate emissions from manure using Tier 1 and Tier 2 methods)
3. Manure Knowledge Kiosk
4. Managing manure to reduce greenhouse gas emissions
5. MRV Platform for Agriculture: Measuring, verifying and reporting GHG emissions from agriculture

Methods and sources of emission factors

1. Owen JJ, Silver WL. 2015. Greenhouse gas emissions from dairy manure management: a review of field-based studies. Global Change Biology.
   • This study synthesized a global dataset on GHG emissions from manure management on dairies, compare the data with modeled values, and identify the greatest mitigation opportunities.
2. Pelster DE, et al. 2016. Methane and Nitrous Oxide Emissions from Cattle Excreta on an East African Grassland. Journal of Environmental Quality.
3. Gonzales-Avalos E, Ruiz-Suarez LG. 2007. Methane conversion factors from cattle manure in México. Atmosfera.
4. See case studies of the methods used to compile Tier 2 livestock GHG inventories at the AgMRV Platform for Agriculture.