Nitrogen Feeds Half the World and Poisons the Rest (2026)

The direct answer to the question this report examines is that nitrogen fertiliser is both indispensable and badly managed. In 2008 a team led by Jan Willem Erisman estimated that nitrogen fertiliser supported 48% of the world's population, up from 44% in 2000, and that across the twentieth century it had made possible some 4 billion births ◈ Strong Evidence [1]. Vaclav Smil, working from different assumptions, put the figure at about 40% ◈ Strong Evidence [2]. Our World in Data, reviewing the literature in 2022, found that estimates tend to converge on a range of 40% to 50%, with a 2023 study by Rosa and Gabrielli placing the share at about half in 2019 ✓ Established [3]. Whichever figure is used, no other single industrial process stands between so many people and hunger. Yet roughly 60% of the nitrogen applied to crops never reaches the harvest ◈ Strong Evidence [6], and that lost majority is where the problem begins.

The scale of production is difficult to grasp. The US Geological Survey estimates that world ammonia output reached 160 million tonnes of contained nitrogen in 2025, up from 156 million tonnes in 2024 ✓ Established [4]. China alone produced 49 million tonnes, followed by India and Russia at 15 million tonnes each, the United States at 14 million and Indonesia at 6 million ✓ Established [4]. Around 80% of the ammonia made by Haber-Bosch ends up as fertiliser ✓ Established [1], and global nitrogen fertiliser consumption exceeded 115 million tonnes in 2023, led by China at 26.3 million tonnes, India at 20.5 million and the United States at 11.6 million ◈ Strong Evidence [5]. In the words of the USGS, nitrogen is an essential plant nutrient that has no substitute ✓ Established [4].

That production pushes the global nitrogen cycle far outside its natural range. In 2023 a team led by Katherine Richardson updated the planetary boundaries framework and set the safe limit for industrial and intentional biological nitrogen fixation at 62 teragrams a year, with a zone of increasing risk extending to 82 ✓ Established [9]. The current figure is about 190 teragrams — roughly three times the boundary ✓ Established [9]. Earlier work by Will Steffen and colleagues in 2015 had already found the boundary transgressed; the higher 2023 number partly reflects a change in method rather than a tripling of use. Either way, nitrogen is among the most heavily breached of the nine boundaries, alongside climate change and biodiversity loss.

The third dimension is economic. Because ammonia is made from hydrogen stripped from natural gas or coal, the price of fertiliser moves with the price of fossil fuels and with the geopolitics of the countries that export them. In 2021 and 2022 the World Bank's fertiliser price index rose by more than 100% and 55% respectively ✓ Established [32]. In 2026 the market was hit again: after the Strait of Hormuz was declared closed in early March, urea prices rose above 850 dollars a tonne in April, up 80% since February ✓ Established [32]. Two price shocks in five years have shown how quickly a molecule taken for granted becomes a strategic commodity.

These three facts — dependence, leakage and price exposure — are usually discussed separately. Agronomists talk about yields, ecologists about dead zones, climate scientists about nitrous oxide and traders about gas spreads. The argument of this report is that they are one system with a single point of failure: a process invented in 1909 that converts fossil energy into food at a global efficiency so low that most of the product becomes pollution. The European Nitrogen Assessment estimated in 2011 that nitrogen pollution costs Europe between 70 billion and 320 billion euros a year, more than double the extra farm income that nitrogen fertiliser generates ◈ Strong Evidence [22]. The fertiliser is cheap at the farm gate largely because its full costs are paid elsewhere.

Nor is the burden evenly shared. Per person, nitrogen fertiliser use runs at about 40 kilograms a year in North America and 25 to 30 kilograms in Europe, but only 2 to 3 kilograms in Africa ✓ Established [19]. Across Western Africa, mineral nitrogen use averaged 4.1 kilograms per hectare of cropland in 2023, against 192.4 kilograms in China ✓ Established [55]. One part of the world uses too much and loses most of it to rivers and air; another uses too little to close yield gaps. The sections that follow examine how the process works, where the lost nitrogen goes, who pays for it, how gas and war set its price, how five policy regimes have tried to manage it, and what the contested evidence actually supports.

The Haber-Bosch process combines nitrogen from the air with hydrogen at high temperature and pressure over an iron catalyst. Fritz Haber demonstrated a working laboratory apparatus to BASF on 2 July 1909, and the first commercial plant began production on 9 September 1913, just over four years later ✓ Established [2]. The engineering problem — building steel vessels that could survive the pressures involved — was solved by Carl Bosch, who backed the project against internal scepticism ✓ Established [2]. Haber received the Nobel Prize in Chemistry for 1918 and Bosch shared the prize in 1931 ✓ Established [1]. Before then, farmers depended on manure, legume rotations, guano and mined Chilean nitrate, supplies that the chemist William Crookes had warned in 1898 would not feed a growing world ◈ Strong Evidence [58].

The nitrogen in the air is free; the hydrogen is not. According to the International Energy Agency's Ammonia Technology Roadmap, 72% of global ammonia was made from natural gas in 2020 and 26% from coal, with electrolysis accounting for a fraction of a percentage point ✓ Established [20]. The sector used about 8.6 exajoules of energy, or 2% of total final energy consumption, and emitted about 450 million tonnes of carbon dioxide, or 1.3% of energy-system emissions ✓ Established [20]. Ammonia production consumed around 170 billion cubic metres of natural gas, equivalent to 20% of all industrial gas demand ✓ Established [20]. Erisman and colleagues put the theoretical energy floor of fixation at 32 megajoules per kilogram of nitrogen ✓ Established [1]. Food security, in short, has been built on a gas pipeline.

The climate cost extends well beyond the factory. A 2022 study in Scientific Reports by Stefano Menegat, Alicia Ledo and Reyes Tirado estimated that the full supply chain of synthetic nitrogen fertiliser emitted 1.13 billion tonnes of carbon dioxide equivalent in 2018, or 2.1% of global greenhouse gas emissions ◈ Strong Evidence [19]. Manufacturing accounted for 38.8% of that total, transport for 2.6%, and emissions from the field — mainly nitrous oxide released as soil microbes process surplus nitrogen — for 58.6% ◈ Strong Evidence [19]. The larger share of the climate damage therefore happens after the fertiliser is spread, which is why cleaner factories alone cannot solve the problem.

The deeper weakness is efficiency. A 2015 study in Nature led by Xin Zhang and Eric Davidson estimated that the global average nitrogen use efficiency of crops is about 0.4: only about 40% of the nitrogen applied ends up in the harvested crop, and the rest is lost to air, water and soil ◈ Strong Evidence [6]. To meet food and environmental goals by 2050, the authors calculated, that efficiency would need to rise to about 0.7 ◈ Strong Evidence [6]. Erisman's team found that the efficiency of cereal production had fallen from about 80% in 1960 to around 30% in 2000, as farmers applied more nitrogen to capture smaller marginal gains ◈ Strong Evidence [1]. Estimates vary with definitions and system boundaries, but every major assessment finds that most of the nitrogen is wasted ⚖ Contested [6] [7].

China illustrates the pattern most sharply. A county-scale study by Chen and colleagues, citing China's Ministry of Agriculture, put the country's cropland nitrogen use efficiency at about 32% in 2017, against a world average of 55% on the ministry's definition ◈ Strong Evidence [7]. China accounts for close to 30% of global fertiliser use, and in most Chinese counties efficiency sits between 20% and 40% ◈ Strong Evidence [7]. Zhang described China's performance as among the lowest in the world, warning that continuing on the same path would lead to an even more significant nitrogen-pollution problem than exists today ✓ Established [6]. Yet China has also become the strongest evidence that efficiency can improve, a point examined in section six.

Low efficiency has a simple economic logic. Fertiliser has historically been cheap relative to the value of the crop it protects, so applying an extra margin is a rational insurance policy for a farmer facing uncertain weather. The losses that result — nitrate in groundwater, ammonia in the air, nitrous oxide in the atmosphere — are borne by downstream water users, city residents and the climate rather than by the farm. Erisman and colleagues noted that the number of people supported per hectare of arable land rose from 1.9 in 1908 to 4.3 in 2008 ✓ Established [1]. That achievement is real. So is the fact that it was purchased with an input whose waste is priced at zero.

Nitrogen that escapes the field does not disappear. Some leaches into groundwater as nitrate, some washes into rivers, some volatilises as ammonia and some is converted by soil bacteria into nitrous oxide. In rivers and coastal seas, the extra nitrogen fertilises algal blooms; when the algae die and sink, their decomposition consumes the oxygen in the water below. A 2008 review in Science by Robert Diaz and Rutger Rosenberg counted dead zones in more than 400 systems covering more than 245,000 square kilometres, and found that their number had grown exponentially since the 1960s ✓ Established [10].

A decade later, an international team led by Denise Breitburg updated the picture. More than 500 coastal sites had reported oxygen concentrations of 2 milligrams per litre or less since 1950, and fewer than 10% of those systems had been known to suffer hypoxia before 1950 ✓ Established [11]. The volume of anoxic water in the open ocean had more than quadrupled over the same period ✓ Established [11]. The authors linked the coastal trend directly to nutrient loading: global fertiliser use rose tenfold after 1950, and the nitrogen carried by rivers to the coast rose by 43% between 1970 and 2000 ✓ Established [11].

The best-measured example is in the Gulf of Mexico, now called the Gulf of America by the US federal government, where the Mississippi and Atchafalaya rivers deliver nitrogen from the farms of the American Midwest. In 2024 NOAA-supported scientists measured the hypoxic zone at 6,705 square miles, the 12th largest in 38 years of measurement ✓ Established [13]. In 2025 it covered 4,402 square miles, the 15th smallest on record ✓ Established [14]. A single smaller year is not a trend: the five-year average stood at 4,755 square miles, more than double the target of 1,900 square miles that the federal Hypoxia Task Force has set for 2035 ✓ Established [14].

The Baltic Sea offers a European parallel. Research by Jacob Carstensen and Daniel Conley, summarised by Lund University, found that the area of oxygen-depleted bottom water grew from about 5,000 square kilometres around 1900 to some 60,000 square kilometres, with most of the expansion after 1950 ◈ Strong Evidence [15]. The Baltic is a semi-enclosed sea with slow water exchange, which makes it unusually sensitive, but the driver is the same: nutrient runoff from farmland and wastewater across the countries that surround it. Unlike the open ocean, coastal dead zones respond to what happens on land, which means they can recover when nutrient loads fall.

The second escape route is the atmosphere. The Global Carbon Project's nitrous oxide budget, led by Hanqin Tian and published in 2024, found that atmospheric concentrations had risen from 270 parts per billion in 1750 to 336 parts per billion in 2022 ✓ Established [16]. Human emissions rose by 40% between 1980 and 2020, and agriculture was responsible for 74% of anthropogenic emissions in the 2010s ✓ Established [16] [17]. Observed concentrations have exceeded the levels projected under all of the scenarios used in the sixth round of the Coupled Model Intercomparison Project ✓ Established [16]. Pep Canadell of CSIRO noted that growth rates in 2020 to 2022 were 30% higher than in any previous year since 1980 ✓ Established [17].

Nitrous oxide is a potent and persistent gas. The US Environmental Protection Agency, using the values in the IPCC's Sixth Assessment Report, gives it a 100-year global warming potential of 273 times that of carbon dioxide and an atmospheric lifetime of more than a century ✓ Established [18]. China was the largest emitter in 2020, at 16.7% of the global total, followed by India at 10.9% and the United States at 5.7% ✓ Established [17]. Europe is the notable exception: its emissions fell by 31% over the four decades, showing that the trend is not fixed ✓ Established [16]. The CSIRO team calculated that human nitrous oxide emissions need to fall by around 20% from 2019 levels by 2050 to stay consistent with the Paris goals ◈ Strong Evidence [17].

The cost of nitrogen pollution is most visible where it enters a tap. On 13 June 2025, Central Iowa Water Works imposed its first-ever ban on lawn watering for about 600,000 customers after nitrate levels in the Raccoon River reached 20.55 milligrams per litre ✓ Established [25]. The US drinking water limit is 10 milligrams per litre measured as nitrate-nitrogen. The utility's nitrate removal facility costs about 16,000 dollars a day to run and can treat only 10 million gallons a day against summer demand of 70 to 80 million ✓ Established [25]. A utility official put the cause plainly: everything coming off the agricultural landscape upstream washes down to the city's intakes ✓ Established [25].

Des Moines tried to make the polluters pay. In 2015 the utility sued drainage districts in three upstream counties, arguing that the tile drainage systems that carry water off fields were point sources of pollution under the Clean Water Act. In January 2017 the Iowa Supreme Court ruled that the drainage districts were immune from damages, and the federal case was dismissed in March 2017 ✓ Established [26]. The episode exposed the legal architecture that shields agriculture: under US law, runoff from farmland is classed as nonpoint pollution and is largely exempt from the permitting system that governs factories and sewage plants. Water customers pay for the treatment instead.

The health risk may begin well below the legal limit. A Danish registry study led by Jörg Schullehner followed 2.7 million adults between 1978 and 2011, using more than 200,000 water samples to estimate exposure ◈ Strong Evidence [24]. People exposed to more than 9.3 milligrams of nitrate per litre had a 16% higher risk of colorectal cancer than those exposed to less than 1.3 milligrams, and increased risk appeared from about 4 milligrams per litre ◈ Strong Evidence [24]. The European limit is 50 milligrams of nitrate per litre, more than ten times that threshold. Schullehner noted that the increased risk could be seen at concentrations far below the drinking water standard ◈ Strong Evidence [24]. Causation is not proven by a single cohort, but the finding has prompted calls to revisit standards set decades ago.

Europe's groundwater shows how persistent the problem is. The Commission's evaluation of the 1991 Nitrates Directive, presented in July 2026, found that the share of groundwater monitoring stations at or above the 50 milligram limit reached 25.3% in Germany, 21.7% in Portugal, 14.8% in Denmark and 11.7% in Italy ✓ Established [59]. The European Environmental Bureau, reviewing the same evaluation, put the cost of nitrate pollution at around 22 billion euros a year and said that more than 33% of water bodies are affected by agricultural pollution ◈ Strong Evidence [27]. The evaluation concluded that the directive remains necessary, even as the Commission prepared simplification measures for farmers ✓ Established [27].

Nitrogen also kills through the air. Ammonia released from manure and fertiliser reacts with other pollutants to form fine particulate matter. A 2021 study in the Proceedings of the National Academy of Sciences by Nina Domingo and colleagues estimated that air pollution from US agriculture causes about 17,900 deaths a year, 15,900 of them from food production, with 80% of those linked to animal-based foods ◈ Strong Evidence [28]. Roughly 12,400 of the deaths were attributable to ammonia emissions ◈ Strong Evidence [28]. These deaths rarely feature in debates about farm policy, because the pollution is diffuse and the victims live far from the fields.

Putting the pieces together, the damage is large relative to the benefit. The European Nitrogen Assessment, launched in 2011 by Mark Sutton and colleagues, estimated total annual damage of 70 billion to 320 billion euros across Europe ◈ Strong Evidence [22]. The Colombo Declaration of October 2019, adopted under the UN Environment Programme, estimated that about 80% of the nitrogen humanity mobilises is lost to the environment, worth some 200 billion dollars a year, and committed governments to an aim of halving nitrogen waste by 2030 ✓ Established [23]. Joyce Msuya, then UNEP's deputy executive director, framed the stakes in a single line: humanity's existence depends on nitrogen, but its usefulness has come at a terrible cost ✓ Established [23]. The declaration is not binding, and seven years later the aim still has no enforcement mechanism behind it.

The first warning came in September 2021. As British wholesale gas prices averaged 19.79 dollars per million British thermal units, more than 500% above the 2020 average of 3.20 dollars, CF Industries halted its two UK ammonia plants at Billingham and Ince ✓ Established [37]. The shutdown cut off a by-product few people had considered: food-grade carbon dioxide, used to stun livestock at slaughter and to package meat and drinks. The British government agreed short-term financial support to restart Billingham, an emergency subsidy paid to a fertiliser plant to keep the food supply chain running ✓ Established [37]. In June 2022 CF announced that Ince would close permanently, and in September 2022 it idled ammonia production at Billingham ✓ Established [36].

Russia's invasion of Ukraine in February 2022 turned a gas squeeze into a crisis. The Togliatti-Odesa pipeline, which had carried up to 2.5 million tonnes of Russian ammonia a year across some 2,470 kilometres to Black Sea export terminals, was shut ✓ Established [48]. Russia had supplied around 16% of world nitrogen fertiliser trade in 2020, according to IFPRI ◈ Strong Evidence [49]. By November 2022 the industry association Fertilizers Europe reported that almost 70% of European ammonia production had been halted since August because of gas prices, and the European Commission estimated that fertiliser costs for farmers had risen 110% compared with 2019 ✓ Established [35]. Urea, the most widely traded nitrogen fertiliser, became a barometer of the war.

Not everyone lost. Producers with access to cheap gas, notably in North America, sold into a world market priced by the most expensive European plants. CF Industries reported 2022 net earnings of 3.35 billion dollars, up from 917 million dollars in 2021 ✓ Established [36]. Yara, headquartered in Norway, reported record 2022 earnings before interest, tax, depreciation and amortisation, excluding special items, of 4.889 billion dollars ✓ Established [38]. US Gulf Coast ammonia averaged 1,070 dollars per short ton in 2022, against about 450 dollars in 2025 ✓ Established [4]. Whether those margins reflected scarcity or market power is one of the contested questions examined in section seven ⚖ Contested [47].

Then came the second shock. After the Strait of Hormuz was declared closed in early March 2026, the World Bank reported that urea prices rose above 850 dollars a tonne in April, up 80% since February, noting that the Middle East supplies nearly a quarter of world urea exports ✓ Established [32]. Its April 2026 Commodity Markets Outlook forecast fertiliser prices up 31% for the year, driven by a rise of about 60% in urea, and warned that affordability would be the worst since 2022 ✓ Established [33]. The International Trade Centre found that urea exports from economies dependent on the strait fell by 83% in volume in April 2026 compared with a year earlier, and that the Gulf normally supplies 43% of seaborne urea ✓ Established [43].

Other governments then made the shortage worse. China, which had exported about 4.9 million tonnes of urea in 2025, banned many fertiliser exports in March 2026 and later issued a quota of around 1.5 million tonnes, according to Reuters reporting ◈ Strong Evidence [45]. Beijing had already restricted shipments in 2024, when its nitrogen exports fell by more than 90% year on year ✓ Established [34]. India, which had sourced more than 40% of its urea and diammonium phosphate from the Middle East, scrambled for alternative suppliers ◈ Strong Evidence [45]. Indian import tenders cleared at 935 to 959 dollars a tonne, against 410 to 420 dollars a year earlier ◈ Strong Evidence [46]. Export restrictions by large producers turned a regional shipping disruption into a global price event.

Europe's response has pulled in two directions. To deny Moscow revenue, the EU imposed duties on Russian and Belarusian nitrogen fertilisers from 1 July 2025, combining a 6.5% tariff with a levy of 40 to 45 euros a tonne that rises to 430 euros a tonne in 2028 ✓ Established [39]. Latvian rapporteur Inese Vaidere argued that the measure would help prevent Russia from using the EU market to finance its war machine ✓ Established [40]. From 1 January 2026, fertiliser imports also entered the definitive phase of the Carbon Border Adjustment Mechanism, adding an estimated 43 euros a tonne to Egyptian urea ◈ Strong Evidence [41]. Within weeks the Commission proposed suspending ordinary tariffs on urea and ammonia from other suppliers to offset those costs ✓ Established [41]. By May 2026, with EU nitrogen prices about 70% above their 2024 average, Brussels published a Fertiliser Action Plan offering targeted support through farm policy instruments ◈ Strong Evidence [42].

China is the clearest case of reform at scale. In February 2015 the agriculture ministry launched a Zero Growth Action Plan for fertiliser use by 2020. According to the China Statistical Yearbook, total fertiliser use then fell from 60.23 million tonnes in 2015 to 52.51 million tonnes in 2020, a decline of 12.8% ✓ Established [52]. Mineral nitrogen use per hectare of cropland fell from 235.4 kilograms in 2014 to 192.4 kilograms in 2023 ✓ Established [55]. A 2024 study in Nature Food led by Carnegie Science researchers found that Chinese nitrogen use efficiency improved by 18% between 2007 and 2017, while yields rose 10% and nitrogen pollution fell 8% ◈ Strong Evidence [8]. China still applies far more nitrogen per hectare than any other major producer, but it has shown that use can fall without a collapse in output.

India illustrates the opposite incentive. Urea is sold to farmers at a fixed, heavily subsidised price, which encourages overuse relative to other nutrients. The fertiliser subsidy bill for fiscal 2025-26 reached about 2.11 lakh crore rupees, 22% more than the year before ◈ Strong Evidence [60]. Mineral nitrogen use stood at 121.5 kilograms per hectare of cropland in 2023 ✓ Established [55]. The government has promoted nano urea, a liquid product that the cooperative IFFCO says can replace a 45-kilogram bag with a 500-millilitre bottle. A two-year field trial at Punjab Agricultural University found wheat yields 21.6% lower and rice yields 13% lower when nano urea replaced conventional nitrogen ⚖ Contested [53]. The claim that technology can substitute for tonnes of fertiliser has not survived independent testing.

The Netherlands shows what happens when nitrogen law meets politics. In 2019 the Council of State struck down the government's system for permitting nitrogen emissions near protected habitats, freezing thousands of construction and farm permits. Plans to buy out and close livestock farms provoked mass protests, and in March 2023 the new Farmer-Citizen Movement, known as BBB, won the provincial elections, taking 17 seats in the Senate ✓ Established [56]. In January 2025 the Hague District Court ordered the state to bring half of its nitrogen-sensitive nature areas below their deposition limits by 2030 or pay Greenpeace a penalty of 10 million euros ✓ Established [50]. Farm leader Ger Koopman of LTO warned of an unprecedented impact on agriculture, housing construction and the Dutch economy ✓ Established [50].

Denmark chose negotiation over litigation. Its Green Tripartite agreement of June 2024 between government, farmers, industry and environmental groups introduced the world's first carbon tax on livestock emissions, starting at 300 Danish kroner per tonne of carbon dioxide equivalent in 2030 and rising to 750 kroner by 2035, with a 60% deduction that lowers the effective rate ✓ Established [51]. The deal also committed 250,000 hectares to new forest and a land fund of 40 billion kroner to take farmland out of production ✓ Established [51]. Climate minister Lars Aagaard stated that agriculture is Denmark's largest emitter and that this cannot continue ✓ Established [51]. The test will be whether nitrogen loads to Danish coastal waters actually fall.

The United States relies on voluntary action. Agricultural runoff is largely outside Clean Water Act permitting, and the Hypoxia Task Force's goals for the Gulf depend on state nutrient reduction strategies and incentive payments. The Gulf dead zone's five-year average remains more than twice the 2035 target ✓ Established [14]. US mineral nitrogen use is relatively low per hectare, at 59.1 kilograms in 2023 ✓ Established [55], but the Corn Belt's tile-drained fields deliver nitrogen to rivers with unusual efficiency. Market structure is also under scrutiny: in March 2026 Bloomberg reported that the Justice Department had opened civil and criminal inquiries into major fertiliser producers, and public comments to the Department of Agriculture said four firms control about 75% of US nitrogen supply ◈ Strong Evidence [47].

Sub-Saharan Africa faces the reverse problem. The 2006 Abuja Declaration set a target of 50 kilograms of fertiliser nutrients per hectare; according to IFDC, African use rose from 8.0 kilograms in 2006 to a peak of 42.5 in 2019 before falling to 34.5 in 2022 ✓ Established [29]. Mineral nitrogen use across Africa averaged only 14.4 kilograms per hectare of cropland in 2023, and 2.0 in Nigeria ✓ Established [55]. At the Africa Fertilizer and Soil Health Summit in Nairobi in May 2024, governments committed to triple domestic production and distribution of certified organic and inorganic fertilisers by 2034 ✓ Established [30]. New Zealand, meanwhile, has capped synthetic nitrogen at 190 kilograms per hectare a year on grazed land since July 2021, though its current government has proposed repealing the cap ◈ Strong Evidence [54].

The first dispute is about the headline number itself. Erisman's 48% figure for 2008 and Rosa and Gabrielli's estimate of about half in 2019 sit at the upper end; Smil's estimate of about 40% for the late 1990s sits lower ⚖ Contested [1] [2] [3]. The difference comes mainly from how much of crop yield is attributed to fertiliser rather than to better seeds, irrigation and management. Erisman's own estimate across the whole twentieth century was 27% of the population ✓ Established [1]. Our World in Data cautions that these estimates are understandably difficult to derive with a high degree of certainty ✓ Established [3]. The careful formulation is that synthetic nitrogen supports somewhere between two in five and one in two people alive today.

The second dispute concerns profits. Critics point to the record earnings of 2022, the concentration of the US market and the 2026 antitrust inquiries as evidence that producers exploit shortages ⚖ Contested [36] [47]. Industry defenders reply that North American plants bought cheap Henry Hub gas while prices were set by the marginal European producer, whose gas costs had risen more than 500% ✓ Established [37]. On that view, the windfalls were a by-product of geography rather than collusion. No charges had been filed by the time of writing, and corn growers' groups were still urging federal action in July 2026 ◈ Strong Evidence [47].

The third dispute is over whether efficiency technology can substitute for limits. China's experience is the strongest evidence for optimism: total fertiliser use fell 12.8% between 2015 and 2020 while efficiency improved ✓ Established [52] [8]. Menegat and colleagues argue that emissions could be cut substantially without compromising food security ◈ Strong Evidence [19]. Sceptics point to the nano urea trials, to the Dutch court's finding that the government lacked a credible plan, and to more than two decades of voluntary programmes in the Mississippi basin without reaching the hypoxia target ⚖ Contested [53] [50] [14]. Technology works when it is measured and enforced; it fails when it is marketed as a substitute for enforcement.

The fourth dispute is about speed. Sri Lanka's 2021 decision to ban synthetic fertiliser overnight is the cautionary tale: according to the International Water Management Institute, rice harvests dropped by 32%, tea production fell 18% and the country lost about 425 million dollars in tea exports ✓ Established [31]. Advocates of rapid transition argue that Sri Lanka failed because it banned inputs without building the alternatives, not because reduction is impossible ⚖ Contested [31]. Their opponents argue that the episode shows how little margin a food system has once it is built around synthetic nitrogen. Both sides agree on one point: any reduction has to come from efficiency first and absolute cuts second.

The disputes look different depending on where they are viewed from. In China, India, the Netherlands and the US Corn Belt, the evidence points to substantial overuse that could be reduced without lowering yields. In much of Sub-Saharan Africa, the evidence points to underuse that keeps yields far below potential ◈ Strong Evidence [29] [55]. A single global message — use less, or use more — fits neither group. The productive form of the debate is regional: where nitrogen is abundant, efficiency and limits; where it is scarce, access and better management from the start.

A final uncertainty concerns low-carbon ammonia. Ammonia made with hydrogen from electrolysis powered by renewable electricity, or from gas with carbon capture, would reduce factory emissions and loosen the link to gas prices. But the IEA reported in 2025 that low-emissions hydrogen still accounts for less than 1% of supply, and it cut its 2030 outlook for low-emissions hydrogen production from 49 million to 37 million tonnes after a wave of cancellations ✓ Established [21] [57]. Even a fully clean factory would leave untouched the 58.6% of supply-chain emissions that occur in the field ◈ Strong Evidence [19]. Cleaner production is necessary, but it does not address the leakage at the core of the nitrogen problem.

The first conclusion is that Haber-Bosch cannot be abandoned on any realistic timescale. Somewhere between 40% and 50% of the world's population depends on it ⚖ Contested [3], Sub-Saharan Africa needs more nitrogen rather than less ✓ Established [29], and the one country that tried to quit synthetic fertiliser overnight lost about 32% of its rice harvest in a season ✓ Established [31]. Any policy that treats nitrogen fertiliser simply as a pollutant to be banned misreads the evidence. The question is not whether to use synthetic nitrogen but how much of what is produced reaches a crop.

The second conclusion is that waste is the central variable. With only about 40% of applied nitrogen reaching the harvest ◈ Strong Evidence [6], and human fixation at about three times the planetary boundary ✓ Established [9], the gap between what is made and what is used drives every downstream harm: the 4,755-square-mile average dead zone in the Gulf ✓ Established [14], the 74% agricultural share of nitrous oxide emissions ✓ Established [17], the nitrate in groundwater from Germany to Iowa ✓ Established [59] [25] and the ammonia-linked deaths in American air ◈ Strong Evidence [28]. Raising efficiency from about 0.4 to 0.7, as Zhang and colleagues propose, would reduce all of them at once ◈ Strong Evidence [6].

The third conclusion is that efficiency responds to enforcement, not exhortation. China's fertiliser use fell 12.8% under explicit national targets ✓ Established [52], and its efficiency improved while yields rose ◈ Strong Evidence [8]. Denmark has bargained a price on livestock emissions and a land fund to retire farmland ✓ Established [51]. By contrast, the voluntary regime in the Mississippi basin has left the dead zone at more than twice its target ✓ Established [14], and India's fixed urea price continues to reward overuse ◈ Strong Evidence [60]. The policies that work make waste costly to the farmer who creates it, or pay farmers directly to produce less of it.

The fourth conclusion is that nitrogen is now a security issue. The shocks of 2022 and 2026 showed that urea prices can jump 80% in weeks when a gas supplier goes to war or a strait closes ✓ Established [32] [35]. Export bans by China magnified both episodes ✓ Established [34] [45]. Europe's response — tariffs on Russian supply, carbon border charges and then emergency suspensions to offset them — illustrates how difficult it is to pursue climate, security and affordability goals at the same time ◈ Strong Evidence [39] [41] [42]. Every tonne of nitrogen that does not need to be applied is a tonne that does not need to be imported.

The fifth conclusion is that the missing piece is measurement. The Colombo Declaration set an aim to halve nitrogen waste by 2030 ✓ Established [23], yet there is no agreed international accounting of nitrogen surplus comparable to national greenhouse gas inventories. Countries report fertiliser sales and crop yields, but rarely the difference between them. Without that number, governments cannot set targets, farmers cannot be rewarded for meeting them and the public cannot see whether policy is working. The European Nitrates Directive evaluation of 2026 found that the law remains necessary after 35 years ✓ Established [27]; the same could be said of nitrogen policy in general.

A century after Fritz Haber's apparatus first ran for five hours in a laboratory, the reaction he discovered feeds billions of people and degrades the water, air and climate on which they depend ✓ Established [1] [2]. Neither fact cancels the other. The evidence does not support abandoning synthetic nitrogen, and it does not support the status quo. It supports a narrower and more demanding goal: making far more of the nitrogen that the world already produces end up in food rather than in rivers, seas and the sky.