80% reduction in carbon emissions from fertilisers possible

According to the researchers manure and synthetic fertilisers emit the equivalent of 2.6 gigatonnes of carbon per year. They found that two-thirds of carbon emissions from fertilisers take place after they are spread on fields, with one-third of emissions coming from production processes.

The researchers mapped the global flows of manure and synthetic fertilisers and their emissions for 2019, along all stages of the lifecycle, by reconciling the production and consumption of nitrogen fertilisers and regional emission factors across nine world regions.

Majority of emisions from fertilisers occur during use

Dr André Cabrera Serrenho from Cambridge’s Department of Engineering said he and his colleagues were surprised to learn that the majority of emissions from fertilisers occur not during production, but during their use.

Emissions from the production of synthetic fertilisers are mostly from ammonia synthesis, partly due to chemical reactions used in the production process. The most effective mitigation at the production stage would be for the industry to decarbonise heating and hydrogen production.

Fertilisers more expensive

Additionally, fertilisers could be mixed with chemicals called nitrification inhibitors, which prevent bacteria from forming nitrous oxide. However, these chemicals are likely to make fertilisers more expensive.

“If we’re going to make fertilisers more expensive, then there needs to be some sort of financial incentive to farmers and to fertiliser companies,” said Serrenho. “Farming is an incredibly tough business as it is, and farmers aren’t currently rewarded for producing lower emissions.”

Also read: Making green ammonia for fertiliser and fuel on-farm

Reduce amount of fertilisers used

The most effective way to reduce fertiliser-associated emissions, however, would be to reduce the amount of fertilisers that are used. “We’re incredibly inefficient in our use of fertilisers,” said Serrenho. “We’re using far more than we need, which is economically inefficient and that’s down to farming practices. If we used fertiliser more efficiently, we would need substantially less fertiliser, which would reduce emissions without affecting crop productivity.”

The researchers also looked at the mix of fertilisers used around the world, which varies by region. The researchers say that replacing some of the fertilisers with the highest emissions, such as urea, with ammonium nitrate worldwide could further reduce emissions by between 20% and 30%. However, this would only be beneficial after decarbonising the fertiliser industry.

Right mix of solutions

“There are no perfect solutions,” said Serrenho. “We need to rethink how we produce food, and what sorts of economic incentives work best. Perhaps that means paying farmers to produce fewer emissions, perhaps that means paying more for food. We need to find the right mix of financial, technological and policy solutions to reduce emissions while keeping the world fed.”

Serrenho and Gao estimate that by implementing all the mitigations they analysed, emissions from the fertiliser sector could be reduced by as much as 80% by 2050.