Approximately 50% of the GHG emissions associated with N fertilizers are attributable to the production process. This is due in part to the energy requirements and use of natural gas in the production process, but also due to the production of nitric acid (as a stage to producing ammonium nitrate) and the leakage of N2O from the plant as part of that process.
Crops need nutrients to grow. Any nutrients required by plants is obtained in the form of minerals which might be organic (e.g. manures, residues or soil organic matter) or mineral fertilizer. Recently, it has been estimated that without mineral nitrogen fertilizers 50% of the world’s population would not be fed, resulting in mass starvation and global crisis (Erisman et al., 2008).
Manufacturing plants that have significantly reduced the N2O 'leakage' will be producing ammonia nitrate fertilizers that have half the potential to heat the earth's atmosphere (or 'Global Warming Potential', GWP) of a plant that has no such technology installed. The process of manufacturing urea also results in approximately half the GWP of a ton of urea compared to a ton of ammonium nitrate from an 'average' ammonium nitrate producing plant.
Determining the GWP of the fertilizer that is used on your farm will therefore make a significant difference to the crop's carbon footprint.
The process of manufacturing fertiliser
N fertiliser is produced using the Haber Bosch process. This involves combining Hydrogen (from steam reforming) with Nitrogen (from the air) to create ammonia. The process is very energy intensive, needed high pressure and high temperature to be most effective, and this comes with a large carbon footprint attached to it.
Work by the International Fertiliser Industry Association (IFA) showed that fertiliser manufacture accounts for approximately 1% of global greenhouse gas emissions. If associated Nitrous Oxide emissions from applying the fertiliser are taken account of as well, the total increases to 2.5% of the global total.
New technologies for reducing emissions.
There are long term solutions that are in development to reduce the emissions associated with fertiliser production. These include carbon capture and storage, renewable electrolysis (to produce the hydrogen rather than the very energy intensive steam process), or the use of biomass gasification. Biomass gasification uses a biomass based feedstock to produce a gas mix which is high in Hydrogen, which can be used to create the ammonia needed. This ammonia is then combined with nitric acid to produce Nitrogen fertiliser (ammonium nitrate). Studies looking at biomass gasification have found that the GWP can be reduced by 52% through using this production method.
As well as the process being energy dense, the other emission associated with fertiliser production is nitrous oxide emissisons which is a by-product of the production of nitric acid. With improvements in best available techniques, the IPCC estimate that nitrous oxide emissions can be reduced to approximately 0.12 kg/tonne nitric acid.
Experiences in China
China’s participation is essential in global efforts in reducing nitrogen related GHG emissions because China is the largest producer and consumer of fertiliser N, accounting for about 30% of global manufacture.
A project developed by Rothamsted Research and China Agricultural University (alongside other colleagues in the UK and China) have been researching different options for reducing the environmental impacts of fertiliser use. They found during the course of the project, that a combination of technical innovations in manufacturing, and changes in how the fertiliser is applied could help to reduce the GHG emissions by between 2-6% of China’s overall greenhouse gas emissions. This is a significant reduction.
Innovation in the UK
One company in the UK who is looking at minimising losses and emissions from production of fertiliser is Yara. The European Union has defined “best available techniques” for the processes associated with fertiliser production. Yara have worked on measuring the carbon footprint from fertiliser production and through the use of new technologies. One example of this is their catalytic cleansing technology with abates about 90% of nitrous oxide emissions associated in the production of nitric acid.
For more information on the work done by Yara click here to visit their Fertilizer Industry Handbook (January 2017).
What can we do?
In terms of practical measures that we can do at home, the only real option for anyone seriously interested in the emissions from fertiliser production is to ask questions and buy from producers who are minimising emissions. Moving forward more innovations will lead to a more streamlined process and fertiliser manufacturers will become streamlined in their environmental credentials.
The best way to minimise losses from fertiliser on the farm is to make sure that they are applied in the most efficient way possible. This will mean that the proportion of the emissions that arises from application is reduced, and also that more of the Nitrogen is used to grow profitable crops rather than lost into the environment.