Producing fertiliser without carbon emissions
Intensive agriculture is possible only if the soil is fertilised with nitrogen, phosphorus and potassium. While phosphorus and potassium can be mined as salts, nitrogen fertiliser has to be obtained laboriously from nitrogen in the air and from hydrogen. And the production of hydrogen is extremely energy-intensive, currently requiring large quantities of natural gas or, as in China, coal.
Paolo Gabrielli, Senior Scientist at the Laboratory of Reliability and Risk Engineering at ETH Zurich in Switzerland, has collaborated with Lorenzo Rosa, Principal Investigator at the Carnegie Institution for Science in Stanford/USA, to investigate various carbon-neutral production methods for nitrogen fertiliser.
In a study published in the journal Environmental Research Letters, the two researchers conclude that a transition in nitrogen production is possible and that such a transition may also increase food security. However, alternative production methods have both advantages and disadvantages. The two researchers examined three alternatives:
- Producing the necessary hydrogen using fossil fuels as in business-as-usual, only that instead of emitting the greenhouse gas CO2 into the atmosphere, it is captured in the production plants and permanently stored underground (carbon capture and storage, CSS). This requires not only an infrastructure for capturing, transporting and storing the CO2, but also more energy. Nevertheless, it is a comparatively efficient production method. However, it does nothing to reduce dependence on fossil fuels.
- Electrifying fertiliser production by using water electrolysis to produce the hydrogen. This requires an average 25 times more energy than today’s production method using natural gas, so it would take huge amounts of electricity from carbon-neutral sources.
For countries with an abundance of solar or wind energy, this might be an appealing approach. However it could lead to competition for sustainable electricity.
- Synthesising the hydrogen for fertiliser production from biomass. Since it requires a lot of arable land and water, ironically, this production method competes with food production. But the study’s authors point out that it makes sense if the feedstock is waste biomass – for example, crop residues.
The scientists state that the key to success is likely to be a combination of all these approaches depending on the country and on specific local conditions and available resources. In any case, it is imperative that agriculture makes a more efficient use of nitrogen fertilisers, the scientists note.
India and China at risk
In the study, the scientists also sought to identify those countries throughout the world in which food security is currently particularly at risk owing to their dependence on imports of nitrogen or natural gas. These are India, Brazil, China, France, Turkey and Germany.
In many cases, decarbonising fertiliser production would reduce this vulnerability and increase food security. At the very least, electrification via renewables or the use of biomass would reduce the dependence on natural gas imports.
However, the researchers point out that all carbon-neutral methods of producing nitrogen fertiliser are more energy intensive than the current method of using fossil fuels. In other words, they are still vulnerable to certain price shocks.
Nitrogen producers facing change
Decarbonisation is likely to change the line-up of countries that produce nitrogen fertiliser, the scientists pointed out in their study. As things stand, the largest nitrogen-exporting nations are Russia, China, Egypt, Qatar and Saudi Arabia. Except for China, which has to import natural gas, all these countries can draw on their own natural gas reserves. In the future, the countries that are likely to benefit from decarbonisation are those that generate a lot of solar and wind power and also have sufficient reserves of land and water, such as Canada and the USA.
“There’s no getting around the fact that we need to make agricultural demand for nitrogen more sustainable in the future, both for meeting climate targets and for food security reasons,” the Swiss scientist Gabrielli concludes.
Rosa L, Gabrielli P: Energy and food security implications of transitioning synthetic nitrogen fertilizers to net-zero emissions, Environmental Research Letters 2022, doi: external page10.1088/1748-9326/aca815call_made