How does the Intergovernmental Panel on Climate Change Tier 2 method work out manure methane per cow, and what changes if the dung is stored as slurry?

Tier 2 multiplies daily volatile solids, 365, the methane capacity of the manure and 0.67, then the share of manure in each system times its methane conversion factor. For an Indian cow at 26 degrees Celsius, liquid slurry converts 71% against 1% for daily spreading, so storage choice decides the answer.

The equation

The Intergovernmental Panel on Climate Change (IPCC) 2006 Guidelines, Volume 4, Equation 10.23: emission factor = volatile solids (VS) per day x 365 x (maximum methane-producing capacity (Bo) x 0.67 kilograms (kg) per cubic metre x the sum, over each manure system, of methane conversion factor (MCF) divided by 100 times the share of manure in that system).

VS are the organic material in the manure as excreted. Bo is cubic metres of methane per kilogram of VS. The 0.67 turns cubic metres of methane into kilograms. The MCF is the part of Bo that the system actually reaches, and it depends on temperature and how long the manure sits.

Defaults for an Indian dairy cow

• Table 10A-4, Indian Subcontinent: average cow mass 275 kg, Bo 0.13 cubic metres of methane (CH4) per kg of VS, and 2.6 kg of VS per head per day.
• Manure shares: 51% burned for fuel, 27% pasture, range or paddock, 19% daily spread, 1% liquid or slurry, 1% digester. They add to 99%.

Conversion factors at 26 degrees Celsius (Table 10.17)

• Pasture, range or paddock 2.0%, daily spread 1.0%, solid storage 5.0%, dry lot 2.0%, burned for fuel 10%.
• Liquid or slurry: 71% without a natural crust and 44% with one. Uncovered anaerobic lagoon 79%. Pit storage under the animals for more than a month 71%.
• Anaerobic digester: 0 to 100%, worked out with the guide's Formula 1 from the methane produced, used and flared. Do not guess a number.

What the default adds up to

At 26 degrees the weighted conversion is 0.01 x 71% + 0.27 x 2% + 0.19 x 1% + 0.01 x 10% + 0.51 x 10% = 6.64%. That gives 5.49 kg CH4 per cow, which the table prints as 5. Dung cakes are 5.1 of the 6.64 percentage points, about 77% of the factor. Table 10A-4 puts 10% on the 1% digester share as its own placeholder. A real digester needs Formula 1; at 1% of the manure it moves the total by at most 1 percentage point.

What changes in a slurry shed

If the shed flushes or scrapes dung into a tank or pond, the weight of the answer moves to the liquid line. The guide notes that the estimated reduction from a natural crust cover (40%) is an annual average from a limited data set and can be highly variable.

The defaults (275 kg, 2.6 kg of VS, each given by the table as plus or minus 10 to 20%) are for the regional average cow; Table 10.11 describes Indian dairy cows as low production. A herd fed more excretes more VS. The guide gives Equation 10.24 to work VS out from feed intake and digestibility, and prefers measured Bo where it exists.

One cow and then 100 cows, 26 degrees Celsius

• Capacity at 100% conversion: 2.6 x 365 x 0.13 x 0.67 = 82.66 kg CH4 per cow per year
• Default shares: 82.66 x 0.0664 = 5.49 kg CH4 per cow
• All manure as slurry without crust: 82.66 x 0.71 = 58.69 kg
• All manure in solid storage: 82.66 x 0.05 = 4.13 kg
• All manure spread daily: 82.66 x 0.01 = 0.83 kg
• 100 cows, default: about 549 kg CH4, which is 549 x 27 = about 14.8 tonnes of carbon dioxide equivalent (CO2e)
• 100 cows, all slurry: 5,869 kg CH4, which is 5,869 x 27 = about 158.5 tonnes CO2e

Whole-herd storage choices are example scenarios, not defaults. 27 is the Sixth Assessment Report (AR6) 100-year warming potential for non-fossil methane. Storage nitrous oxide is a separate line.

What Senseible does here

Senseible reads fuel invoices and electricity bills into emission records, so diesel for tractors and pumps and power for the milking shed and chilling tank show up once uploaded. The herd, manure and field figures on this page come from your own farm records.

• Manure methane per cow and buffalo
• Dairy biogas plant carbon credits
• Nitrous oxide from manure storage

Sources: IPCC 2006 Guidelines, Volume 4, Chapter 10, Equations 10.23 and 10.24, Tables 10.17 and 10.18, Annex 10A.2 Table 10A-4, IPCC Sixth Assessment Report, Working Group I, Chapter 7, Table 7.15 (100-year global warming potential: methane of non-fossil origin 27.0, nitrous oxide 273)

Last reviewed 2026-11-05. The cow mass, VS, Bo and shares are 2006 regional defaults. Replace them with your own herd data where you hold it, and keep the same inputs each year.