GHG emissions from urea (fertilizer)

Trevor Brown's picture

I'm searching for data that quantifies what happens to the CO2 in urea, after it is applied as fertilizer. How much (and how fast) does it decompose to enter the atmosphere? Is any sequestered in the soil? Does any realistically get taken up by the plant it is fertilizing?

Any suggestions of a good dataset would be very welcome.

I'm an independent ammonia industry analyst. I track the new fertilizer plants being built and I'm very keen to see new, sustainable technologies replace the old fossil-fueled Haber Bosch process. The new projects that call themselves 'environmentally friendly' do so because they capture all the CO2 emissions at the plant, and use the CO2 to make urea. This strikes me as nonsense environmental accounting - the atmospheric emissions are still there, just outsourced to the farmer.

So - I'm looking for reliable data that I can use to demonstrate that urea production is not carbon sequestration.

The website I run is https://ammoniaindustry.com, and you can reach me at tb@ammoniaindustry.com.

With sincere thanks in advance,

  T.
Trevor Brown

Tara Garnett's picture

 

Hi Trevor this is Tara Garnett (I run the FCRN) but I'm actually replying on behalf of Pete Smith at Aberdeen who sent me his answer but is travelling at the moment so can't post himself.  He writes as follows:

CO2 is not taken up by plants from the soil – all of their CO2 comes from the atmosphere. Because of root respiration, CO2 concentrations around the root are often way higher than atmospheric concentrations, and the roots do not photosynthesise in any case – so they emit CO2 rather than take it up. Any CO2 will be mineralized and lost to the atmosphere, so using urea does not sequester carbon in the soil.

 Hope this helps

Simon Ward's picture
Submitted by Simon Ward on

1.  I had never considered it before (because of the more important nitrous oxide loss (and ammonia loss)) but what does happen to the carbon atom in urea when used as a fertiliser and what is the pathway? While the energy gradient is wrong does any of the carbon get converted to methane through biological activity? Incidentally, while sequestering does not occur in practical and crude terms, for a crop such as wheat, roughly 50% of the nitrogen applied does get incorporated into the soil reserve. Unfortunately a similar amount is released to be taken up by the plant. (Plus ca change...?)

2. There is not necessarily anything wrong with the Haber Bosch process itself. This fundamentally involves combing hydrogen and nitrogen under pressure and at high temperature over a catalyst. Originally the process involved electrolysis to split hydrogen from water and nitrogen from the atmosphere and thus generally used hydroelectric power for the rest of the process - carbon neutral except that rivers were damned and rotting vegetation on the lake bottom releases methane. Thus fertiliser plants are located in Norway. This is no longer true and hydrogen is split from natural gas leaving carbon dioxide as a by-product. Since gas is needed and is a cheap fuel it also provides the energy input. Carbon dioxide can also be sold to fizzy drinks so quite where the boundary is set (in terms of release of GHG) is a conundrum. 

 

Simon Ward

Increment and Inside Track

www.increment.co.uk

www.InsideTrack.org

 

Simon Ward's picture
Submitted by Simon Ward on

Thanks Miguel for you response. I was as interested in the path way. While a subsequent thought I wonder whether under (ghg positive) land use change if the rate of soil carbon accumulation might be enhanced with fertiliser up until the point when soil carbon addition/oxidation reach equilibrium? The soil nitrogen carbon ratio is crucial to soil flora and fauna and, indeed, to the accumulation of say grassland organic matter

Simon Ward

Increment and Inside Track

www.increment.co.uk

www.InsideTrack.org

 

Trevor Brown's picture

Thanks to all at FCRN who responded to my question about the carbon in urea. The issue I was trying to solve was this: everyone says the carbon turns to CO2 and is released to the atmosphere, but I couldn't find ANY data to demonstrate the fact.

Someone at FCRN forwarded my question to the R&D dept at Yara, and they commissioned a lab test to prove it. So, big thanks to the network: excellent resource.

I recently published the piece I was writing - how to think about a "zero-emissions" ammonia plant that, despite using a fossil fuel feedstock, achieved its emissions reduction through carbon capture and utilization, using the CO2 to make urea. Did the local reduction in emissions lead to any global reduction in emissions? (Answer: No.)

If you're interested, it's over here: https://ammoniaindustry.com/urea-production-is-not-carbon-sequestration/

For what it's worth, I discovered a few things in my research:

Essentially all the carbon contained in urea becomes atmospheric CO2 emissions within ~1 week after urea fertilizer is applied to the soil. In terms of a life-cycle analysis, the carbon atoms in urea only represent ~14% of urea's GHG footprint (per Fertilizers Europe). Given the size of the global urea market, that's about 150 million tons of CO2 emissions per year, just from the carbon atom contained in the urea molecule.

Thanks again, all. Best wishes,

  T.
tb@ammoniaindustry.com