Green fertilisers: not a quick fix

Synthetic fertilisers add the major soil nutrients – nitrogen, phosphorus, and potassium – necessary for plant growth. Phosphorus and potassium are mined, whereas nitrogen, which accounts for over half of all synthetic fertilisers, is synthesised from natural gas and coal.

 While sectors such as energy or transport have begun to decarbonise, chemicals used in the agrifood sector – above all food-related plastics and nitrogen fertilisers – remain key drivers of demand for fossil fuels. Both the agrifood and energy sectors are dominated by a small number of large multinational corporations, which have a vested interest in maintaining an industrial food system that depends on fossil fuels.

The production and use of fossil-based nitrogen fertiliser creates several problems. First, greenhouse gas emissions and other environmental impacts arise throughout the life cycle of nitrogen fertilisers, starting with gas or coal extraction, continuing through the production of ammonia, all the way to the farm. The production based on fossil fuels is incompatible with the Paris Agreement on climate change. In addition to the greenhouse gases emitted during production, fertiliser use leads to the emission of nitrous oxide. Finally, the price of nitrogen fertilisers – and thus of food – is closely linked to the volatile price of internationally traded fossil fuels. This has important geopolitical repercussions. The COVID-19 pandemic and Russia’s full-scale invasion of Ukraine are examples of recent events that have sent fertiliser prices soaring. 

The Soil Atlas 2024 presents data and facts about the importance and condition of land, soils and arable land. In numerous graphics and text contributions, it provides a current insight into the condition of and threats to the soils on which we live.

One proposed way to reduce dependency on fossil fuels is to produce so-called green fertilisers. In this process, hydrogen is first generated via electrolysis using renewable power, and then is used to synthesise ammonia. Increased production and use of green fertilisers would allow for a wider geographical distribution of producers and reduce dependency on imported, price-volatile fossil fuels. Green fertiliser can be produced wherever sun, wind, and water are abundant. Several African countries, including Egypt and Kenya, have begun to build production facilities.

Yet, many challenges remain. Currently, just 0.3 percent of the ammonia used to produce nitrogen fertiliser globally can be described as green. While this share is projected to increase, green fertilisers are unlikely to be globally available at competitive prices soon. Green hydrogen could also generate new problems, as it requires land for solar power plants or wind farms. This increases the threat of land grabbing and land use changes that conflict with livelihood activities. Countries with a history of inequitable land ownership and illegal land appropriation, such as Brazil and Nigeria, are at heightened risk. Water consumption is often discussed as a potential future problem related to the production of green hydrogen. An electrolyser needs a minimum of 9 litres of water to produce one kilogram of hydrogen; however, due to inefficiencies in purification and cooling, electrolysis requires between 20 and 30 litres of water per kilogram of hydrogen. This issue is particularly problematic in regions with high renewable energy potential, which often suffer from water scarcity.

While the production process for green fertilisers has a lower impact on the climate, the impact of the product is the same. Globally, twice as much nitrogen is released into the environment than it can absorb, mostly due to the overuse of fertilisers. This excess nitrogen has a range of damaging impacts. First, soil microbes convert nitrogen into nitrous oxide, a greenhouse gas 300 times more powerful than CO₂. Second, nitrogen-tolerant species outcompete more sensitive wild plants and fungi, reducing biodiversity and harming plant health. Third, nitrates find their way into groundwater and the ocean, creating oxygen-depleted dead zones. Fourth, both nitrates in drinking water and ammonia in the air are harmful to human health. Finally, excessive use of synthetic fertilisers acidifies soils and damages soil health. 

Unless the overall volumes of nitrogen fertilisers are reduced, especially in countries with extreme overuse, such as China, Egypt, and the United Kingdom, the nitrogen surplus will still damage water bodies, soils, and ecosystems, irrespective of how the fertilisers are produced. Green fertilisers that have a lower climate impact during the production phase do not address the more significant emissions that arise in the usage phase. At best, they can reduce emissions related to nitrogen fertilisers by about one-third. Lastly, green fertilisers are still external chemical inputs, which can trap farmers in dependency and debt. 

Scenarios that try to keep global temperatures below 1.5 degrees Celsius include steep and immediate reductions in global synthetic fertiliser use and a near phase-out by 2050. However, governments have a primary responsibility to safeguard food production. They must therefore avoid sudden shocks, as occurred in Sri Lanka in 2021, when the government banned the import of agrochemicals. Instead they should promote a managed transition to more sustainable, agroecological farming systems. Locally, sustainably produced, green fertilisers can facilitate this transition. But they are not a panacea. Instead of substituting fossil-based fertilisers with green fertilisers, the focus should remain on longer-term goals, such as improving soil health, reducing waste, and promoting more efficient nitrogen use by producing food rather than animal feed.