How do I calculate N2O and CO2 emissions from synthetic fertiliser use?
Add up the nitrogen in every fertiliser applied to the field, multiply by the IPCC default of 0.01 kg N2O-N per kg N, then convert with 44/28 and a GWP of 273. Add indirect N2O from volatilisation and leaching, and 0.733 t CO2 for each tonne of urea.
Step 1: turn the season's fertiliser schedule into kg of nitrogen
List every application on the plot for the season: product, kg and date. Multiply each by its nitrogen content and add them up. Use the quantity actually applied, not what was bought, if stock is carried between seasons. Work per hectare so plots of different sizes can be combined later.
- Urea: 46% N.
- DAP (18:46:0): 18% N.
- Ammonium sulphate: about 20.6% N.
- Calcium ammonium nitrate: about 25% N.
- NPK grades state N first, so 10:26:26 is 10% N.
- Farmyard manure or compost also adds nitrogen. IPCC Equation 11.1 counts organic N in the same direct N2O term, so include it if the farmer records it, using a tested or stated N content.
Step 2: direct and indirect N2O
The 2019 Refinement to the IPCC Guidelines splits EF1 by climate. If you use it, use it for every field and say so.
- Direct N2O-N = kg N x EF1. The IPCC 2006 Guidelines (Volume 4, Chapter 11, Equation 11.1) give EF1 = 0.01 kg N2O-N per kg N. For flooded rice the default is 0.003.
- Indirect from volatilisation = kg synthetic N x 0.10 (share lost as ammonia and NOx) x 0.01.
- Indirect from leaching and runoff = kg N x 0.30 x 0.0075, applied only where water moves through the soil, such as irrigated or high-rainfall fields.
- Convert N2O-N to N2O by multiplying by 44/28, then to CO2e with 273, the 100-year GWP of N2O in IPCC AR6.
Step 3: CO2 from the urea share only
Of the common fertilisers, only urea carries carbon that is released after spreading: 0.733 t CO2 per tonne of urea under IPCC 2006 Equation 11.13. DAP, ammonium sulphate and most NPK grades add no CO2 at this step. For the full breakdown for one tonne of urea, see the per-tonne answer linked below.
Step 4: from a hectare to a tonne of crop, and which scope
- Divide each plot's per-hectare total by its yield in tonnes per hectare. For a group of farms, add total emissions and divide by total tonnes, rather than averaging the per-tonne figures.
- Farms you own or run: Scope 1.
- Crops you buy from farmers: their field emissions sit in your Scope 3, Category 1, purchased goods.
- Making the fertiliser itself, mainly ammonia production, is a separate upstream emission. Do not mix it into the field figure.
Worked example: one hectare with 250 kg urea and 125 kg DAP
- Nitrogen: 250 x 0.46 = 115 kg N, plus 125 x 0.18 = 22.5 kg N, total 137.5 kg N
- Direct: 137.5 x 0.01 = 1.375 kg N2O-N x 44/28 = 2.161 kg N2O x 273 = 590 kg CO2e
- Indirect: 137.5 x 0.10 x 0.01 + 137.5 x 0.30 x 0.0075 = 0.447 kg N2O-N x 44/28 = 0.702 kg N2O x 273 = 192 kg CO2e
- Urea CO2: 0.25 t x 0.733 = 183 kg CO2
- Total: 590 + 192 + 183 = about 965 kg CO2e per hectare; at a 4.5 t yield, about 214 kg CO2e per tonne of crop
IPCC Tier 1 defaults; the leaching term assumes an irrigated field and the yield is illustrative. Fertiliser manufacture is not included.
What Senseible does here
Senseible does not calculate field N2O or urea CO2; it has no fertiliser emission factors. It can keep your fertiliser purchase invoices, which give the product quantities this calculation starts from.
Sources: 2006 IPCC Guidelines, Volume 4 AFOLU, Chapter 11 (Equation 11.1, Table 11.1, section 11.4), IPCC AR6 Working Group I, Chapter 7, Table 7.15 (GWP100 of N2O), GHG Protocol Corporate Value Chain (Scope 3) Standard
Last reviewed 2026-10-16.