Fertilizer emissions can be cut to about a fifth of current levels by 2050 without the need to develop new technologies, according to a new study.
A study published in the journal Nature Food looks at the production, trade, and use of nitrogen fertilizers worldwide to determine their total greenhouse gas emissions.
A study claims that simply improving crop nitrogen use could halve the demand for synthetic fertilizers, which would reduce their emissions. Some of the other proposed measures include the use of renewable and nuclear energy to increase fertilizer production.
Combining all existing interventions, the researchers conclude that nitrogen fertilizers can be reduced by up to 84% by 2050, which is higher than previously estimated.However, a co-author of the study tells Carbon Brief that this number would be “very difficult” to achieve, “both financially and in terms of practical implementation.”
Strong emission processes
Environmentalist professor Vaclav Smil called nitrogen fertilizers “the most important invention of the 20th century” in an essay published in the journal Nature in 1999.
They generally fall into two categories: organic and inorganic. (The latter is sometimes called chemical, mineral, or synthetic fertilizer.
Organic fertilizers are mostly made from crop residues or animal residues, such as manure or compost. Inorganic or synthetic fertilizers are made from chemically prepared materials. Both fertilizers are used to promote plant growth and increase yield.
Their widespread use has increased global food production, but these fertilizers have also caused many negative environmental effects, such as causing harmful algae in nearby water bodies, soil acidification, and greenhouse gas emissions.
When nitrogen fertilizers are applied to the field, part of the element is released into the environment—washed into the soil, washed into nearby water, or released into the atmosphere as vapor.
Soil microbes break down nitrogen fertilizers to produce nitrous oxide (N2O), a greenhouse gas nearly 300 times more potent than CO2. Furthermore, fertilizer production is an energy-intensive process that accounts for nearly 1.5% of global carbon dioxide emissions.
A 2020 study found that the global use of nitrogen fertilizers in food production could threaten efforts to keep global warming below 2 degrees.
A new study estimates that the production and use of nitrogen fertilizers in food production account for approximately 5% of global greenhouse gas emissions.
The study examines the global flows and emissions of both synthetic and organic fertilizers in 2019. It says that two-thirds of emissions come from the use of nitrogen fertilizers and only one-third come from the production phase.
To track mass flows of nitrogen fertilizers, the researchers used information on fertilizer production and consumption in nine different regions of the world, taking into account how emission-intensive fertilizer production is in each region.
They estimate that the production and use of synthetic nitrogen fertilizers and manure produced 2.6 billion tonnes of carbon dioxide equivalent (CO2e) in 2019. synthetic fertilizers. They write that, therefore, manure is not currently a suitable alternative to synthetic fertilizers in terms of reducing greenhouse gases.
The study examines the possible emission effects of various measures, such as the use of renewable electricity in production, reducing the total demand for fertilizers, and increasing efficiency.
The diagram below shows different future emission scenarios that can be achieved through interventions such as increasing nitrogen efficiency and changing ammonia production methods.
Improving efficiency is “one of the most effective strategies to reduce emissions,” say the researchers.
Currently, the global nitrogen use efficiency of crops is 42%, which means that plants take up only 42% of the nitrogen applied to the soil By increasing that efficiency to 67 percent—about the level reached in the United States and Canada, according to a 2015 study—the new study finds that total fertilizer demand could be reduced by 48 percent by 2050 better efficiency, including proper irrigation, the cultivation of crops that use nitrogen fertilizers better, and using the right fertilizers in the right amount at the right time and in the right place.
In much of the world, the amount of nitrogen used by crops—from both man-made and natural sources—currently “far exceeds crop nitrogen requirements,” the study adds.
The map below, first published in the 2022 Carbon Review of Fertilizers and Climate Change, shows excess nitrogen per hectare of crop worldwide.
To reduce fertilizer emissions, both the production and use of coal must be reduced, according to the study. An electrified system powered by renewable energy can have a significant impact on manufacturing emissions.
The production of the ammonia compound requires nitrogen and hydrogen, which form the backbone of nitrogen fertilizers. Hydrogen is currently produced using fossil gas, but emissions from this process could be reduced by using water and electricity to produce it (a process called electrolysis), using renewable energy sources, or using nuclear energy.
Examining fertilizer use, the study looks at three possible ways to combat emissions: reducing demand, directly reducing nitrogen oxide emissions, and changing the mix of fertilizer types.
Study co-author Dr. André Cabrera Serrenho, an associate professor at the University of Cambridge, says the 84 percent reduction can be achieved in part by changing the form of nitrogen used in fertilizers.
“So if we use ammonium nitrate instead of urea, we can increase the potential reduction even more, from 80 percent to 8
“However, changing the fertilizer mix itself only leads to emissions savings after all.” Under current conditions, if we make this substitution, we are actually putting more emissions into the atmosphere than otherwise.
According to the study, replacing nitrogen in fertilizers does not reduce emissions by itself; it alone leads to a 3% increase in emissions. The reduction is only seen when the substitutions are made together with other measures.
Ammonium nitrate and urea are both sources of nitrogen, but according to a 2021 study, emissions from using ammonium nitrate can be significantly lower than those from urea.
Improving the use of nitrogen would help reduce the demand for nitrogen fertilizers; a reduced demand would in turn significantly reduce emissions.
The study also says that using “nitrification inhibitors” can reduce overall emissions.
Nitrogen inhibitors (pdf) are chemicals added to fertilizers to limit nitrogen loss when the fertilizer is applied to farmland. Loss of nitrogen can cause soil acidification; limestone is often used to combat this acidification. Reducing nitrogen losses also reduces the need for limestone to correct acidification, which reduces total emissions. (When lime reacts with soil acidity, it produces carbon dioxide.
The table below shows the scenario of synthetic fertilizers until 2050 (left) and the impact of the different measures discussed in the emissions study (right).
Serrenho says that cleaner energy sources are a “very important” factor in reducing carbon dioxide emissions from fertilizers, adding:
“We know that one of the measures we must take to reduce carbon dioxide emissions in society is to electrify everyone. our energy use and electricity production, whether from renewable energy sources or from nuclear energy. .
“If we intend to produce hydrogen in ammonia production and fertilizer production, which we use to produce ammonia by electrolysis, then we need a significant amount of electricity . . must be renewable or nuclear, otherwise we still have significant emissions from ammonia production.
Many of these emission reduction measures can be implemented simultaneously, “thus increasing the overall mitigation effect”, write the researchers.
Professor Mark Sutton, an environmental physicist at the UK’s Center for Ecology and Hydrology, welcomed the “optimism” of mitigation approaches, adding that the research comes at a useful time after a global target to reduce food loss has been set.
The goal (pdf) agreed at the COP15 biodiversity summit in Montreal aims to halve the loss of nutrients to the environment by 2030. Sutton tells “I think what’s really new [in research] is saying ‘we can’ at a very high level, and so it’s a challenge to the community for people who say we can’t.
“I have not seen that all emissions from all sources combined show such ambition.”
Some combinations of interventions produce very large reductions by mid-century. One of the researchers’ scenarios suggests that total emissions in 2050 could be reduced by up to 78% if water electrolysis for ammonia production is combined with a reduction in fertilizer production and the use of nitrification inhibitors.
The study adds that all of the interventions studied have “high-tech readiness,” meaning that they can be but mitigation options may not be easy to implement. everywhere, the study says. For example, newer production plants may be able to use water electrolysis and electric heating for ammonia synthesis. However, in older plants it may be easier to integrate carbon capture and storage (CCS) into existing equipment.
Geographical differences in the availability of suitable carbon capture and storage pools or wind energy can also affect the local adaptation of initiatives. In the electric heating scenarios of the study, it is assumed that wind energy will produce heat for production, but the extent of this possibility varies in different parts of the world.
Sutton says this study should inform the debate about actions to reduce fertilizer emissions and improve overall efficiency, adding:
“The next step is how to get there. How to get the business off the ground and show that the company has a chance if they are a leader of change, not a follower.