Hi,
I found some older ecoinvent carbon emission factors for fertilizers, such as:
"ammonium nitrate phosphate, as N": 4.9 kg CO2e / kg chemical
"ammonium nitrate phosphate, as P2O5": 1.1 kg CO2e / kg chemical
"potassium sulphate, as K2O": 0.7 kg CO2e / kg chemical
I looked at the SDS of a specific fertilizer and it is made out of 40% ammonium nitrate, 30% potassium sulphate and 30% phosphate salts. The N:P:K of the fertilizer is 10 : 5 : 8. How do I correctly apply the above emission factors? My approach so far:
70% of the fertilizer is ammonium nitrate phosphate and 30% is potassium sulphate. For the 70% fraction, I can use the emission factor for ammonium nitrate phosphate, and for the 30% the emission factor for potassium sulphate. Furthermore, the N:P:K ratio shows me how much nitrogen, phosphorus and potassium I have.
100 kg of fertilizer = 70 kg of ammonium nitrate phosphate with 10% nitrogen and 5% phosphorus. This means, 7 kg of ammonium nitrate phosphate, as N, and 3.5 kg of ammonium nitrate phosphate, as P.
Then I have 30 kg of potassium sulphate with 8% potassium, which is 2.4 kg of "potassium sulphate, as K2O".
Or is this incorrect, because the N:P:K of the fertilizer is for the whole product and not for the individual compounds? For example:
100 kg of fertilizer = 10 kg of N, 5 kg of P and 8 kg of K.
Then I calculate 10 kg as "ammonium nitrate phosphate, as N" and "5 kg of ammonium nitrate phosphate, as P", an "8 kg of potassium sulphate, as K2O"?
Happy for some guidance with this.
First compute the production stage emissions- (1) energy & emissions to procure raw material, manufacture synthetic fertilizer in the factor & transport to farm, (b) emissions due to farm application e.g. soil carbon release in nitrogen fertilizations. The first component is often ignored- called scope 2 or 3 emissions, as the later are focussed @Matt Sol.
Utkarsh Ghate
Thank you for hour response but I'm not sure if it really answers my question? Can you pelase elaborate?
- We already calculate and include emissions due to farm application. I think the bigger thing here is emissions due to conversion of nitrogen fertilizer to nitrous oxide, rather than carbon release from soil. Of course, this can happen to but requires too much analysis for this project to really understand the net gain/losses. Because it is also possible to get increased plant growth, thus increased carbon sequestration in the soil.
- About the production stage emissions: Yes, I'm trying to compute it using the ecoinvent emission factors. But I'm not sure how to correctly apply it to a NPK fertilizer, see my original question above. I'm fairly sure it is as follows:
1. Look at the fertilizer SDS to identify its main ingredients.
2. Record the NPK concentration of the fertilizer (e.g., 8-5-8)
3. Calculate the amount of nitrogen, phosphorus and potassium based on (2)
4. Apply the emission factor which closest aligns to (1) and multiply it with (3).
But it would be nice to get some confirmations or comments.
Matt Sol you are on track. Yes, there is conversion factor NxOy wrt Co2 risk by that you can use as the later is upto 300 times risky than the former (e.g. https://www.nature.com/articles/s41612-022-00265-3:- N2O is a long-lived greenhouse gas (GHG) with a global warming potential of about 265‒298 times greater than CO2). The 3rd part- transport emissions from factory to farm is straightforward besides 2 you computed- manufacture & application.
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