Smarter fertilizer use could shrink our agricultural carbon footprint

A new study shows how fertilizer emissions could drop 80 percent by 2050.
A small, young plant sprouts up from dark soil.
A small, young plant sprouts up from dark soil. Deposit Photos

It’s no secret that agriculture is a huge source of climate-change inducing greenhouse gasses. From methane in beef production to synthetic fertilizers, there’s a lot of work to be done in making our food systems climate-friendly.

Manure and synthetic fertilizers emit the equivalent of 2.6 gigatonnes of carbon annually—enough to fill 26,000 aircraft carriers by weight. That’s more than global shipping and aviation combined.  

[Related: Compost can help protect us from food poisoning.]

Organic fertilizers include manure, compost, or bone meal and are derived from animal or plant sources.  Synthetic fertilizers, which often contain only a few nutrients lost from the soil, instead go through a manufacturing process, even if many come from naturally occurring mineral deposits.

But how much is produced, hasn’t really been quantified. 

“Incredibly, we don’t actually know how many chemicals we produce globally, where they end up, where and how they accumulate, how many emissions they produce, and how much waste they generate,” said André Cabrera Serrenho, an environmental engineer from Cambridge’s Department of Engineering, in a statement.

While it’s necessary to reduce the amount of carbon emitted from fertilizers, it has to be done so in a way that doesn’t jeopardize global food security. Previous studies have estimated that 48 percent of the global population consumes crops that are grown using synthetic fertilizers and that the world’s population is projected to reach 9.8 billion by 2050.

For the first time, researchers have calculated and quantified the full life cycle of fertilizers, and their findings published February 9 in the journal Nature Food found that carbon emissions from fertilizers could be reduced by as much as 80 percent by 2050. 

Serrenho, an author of the study, and co-author Yunhu Gao undertook a project to accurately measure the complete impact of these fertilizers on the carbon cycle. 

“In order to reduce emissions, it’s important for us to identify and prioritize any interventions we can make to make fertilizers less harmful to the environment,” said Serrenho. “But if we’re going to do that, we first need to have a clear picture of the whole lifecycle of these products. It sounds obvious, but we actually know very little about these things.”

The team looked at data from 2019 and mapped out the global flows of manure and synthetic fertilizers and their emissions throughout their life cycles across nine regions of the world. They found that two thirds of emissions for fertilizers occurred while they were being used and not during production. 

“It was surprising that this was the major source of emissions,” said Serrenho. “But only after quantifying all emissions, at every point of the life cycle, can we then start looking at different mitigation methods to reduce emissions without a loss of productivity.”

[Related: Wastewater could be the secret to eco-friendly fertilizer.]

The authors found that the most effective mitigation tactic at the production stage would be for the industry to decarbonize the heating and hydrogen creation from the process. The fertilizers could also be mixed with nitrification inhibitors, chemicals which prevent bacteria from forming nitrous oxide. The downside is that these chemicals are likely to increase the cost of fertilizers.

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

Reducing the amount of fertilizer used across the board would be the most effective way of reducing the emissions associated with them. Some of the methods the study evaluated include using water electrolysis during fertilizer production that can keep methane from forming and using nitrogen inhibitors in the fertilizer when it is in the field.  

[Related: Potty-trained cows could seriously help the planet.]

“We’re incredibly inefficient in our use of fertilizers,” said Serrenho. “We’re using far more than we need, which is economically inefficient and that’s down to farming practices. If we used fertilizer more efficiently, we would need substantially less fertilizer, which would reduce emissions without affecting crop productivity.”

While Serrenho said there are “no perfect solutions,” research like this will be critical in rethinking how food is produced and the economic incentives that work best to implement change.

“Our work gives us a good idea of what’s technically possible, what’s big, and where interventions would be meaningful,” said Serrenho. “It’s important that we aim interventions at what matters the most, in order to make fast and meaningful progress in reducing emissions.”