Beware of the N-bomb

July 5, 2019

There are good, and frightening, reasons to closely follow the changes in the nitrogen cycle. We should not be surprised if the effects and costs of disturbing it turn out to be as dramatic as those for the carbon cycle. In addition, greenhouse gas emissions from nitrogen fertilizers are around 3% of global emissions, but they are not visible in greenhouse gas inventories. The abolition or drastic reduction in the use of chemical fertilizers is a pre-condition for a sustainable food system.

In farming, the availability of nutrients, particularly of nitrogen, potash and phos­phorus – mostly referred to by their chemical symbols N, P and K – is a major limiting factor. All traditional farming systems have had some strategy for replacing nutrients in the soil. One is to rest the soil and allow a natural re-charge and release of nutrients from the soil and through atmospheric decomposition. Crop rotations with leguminous crops can fix nitrogen from the air and the nutritional demands of the various crops can complement each other. Phosphorous, from deeper layers or bound in the soil, can be ‘mined’ by some crops making it available to others. Nutrients can also come from irrigation water (especially sediments in flood waters), animal manure, human waste, plants, grass and other residues, a plethora of natural organic fertil­izers. Farmers have used oil-cakes, feathers, leathers, bone, sea weed and fish as fertilizers. There are even reports that human remains from battlefields and ossuaries have been used as fertilizers. Yet all these methods have some limitations, and in most cases they require a lot of work or other efforts.

A farming system dependent on and caused by synthetic fertilizers, Mato Grosso, Brazil Photo: Gunnar Rundgren


It is therefore no wonder that the farmers of the world took to artifi­cial fertilizers with enthusiasm. They are easier to transport than bulky organic materials such as manure, easier to apply and give somewhat predictable results. Global annual use of nitrogen fertilizers increased from 11 million tons in 1960 to 115 million tons in 2017. Contrary to common belief most of the fertilizers are not used to replace what is removed by the crop from the field. The quantities applied mostly surpass this many times. Most nitrogen is simply wasted through denitrification, leaking, erosion and volatilization of ammonia.[i] According to David Montgomery, an American soil scientist, half of the fertilizer used in the United States is used to compensate the nutrient losses caused by erosion. Globally, the nitrogen efficiency in grain production has deteriorated drastically and rapidly (probably mostly a result of decreasing marginal return). Around 1960, each ton of chemical fertilizer resulted in an increase in grain yield of 75 tons, whereas at the end of 1990 this resulted in just 25 tons.[ii]

The greatest single experiment in global geoengineering ever made

Reflecting on his promotion of chemical fertilizers von Liebig ex­claimed: “I have sinned against the wisdom of the Creator and, justly, I have been punished. I wanted to improve his work because, in my blindness, I believed that a link in the astonishing chain of laws that govern and constantly renew life on the surface of the Earth had been forgotten. It seemed to me that weak and insignificant man had to redress this oversight.”[iii] Had von Liebig lived now, he would be even more worried and remorseful.

The quantity of biologically active nitrogen released annually into the biosphere has increased nine-fold in 100 years and nitrogenous fertilizers are the main source of this. In one of the most influential scientific articles of last decade, Planetary boundaries: Exploring the safe operating space for humanity, professor Johan Rockström and colleagues identify the nitrogen cycle as one of three areas – together with climate regulation and biological diversity – where modern civilization has surpassed a threshold for stable development.

Without knowing it, the average European bears costs of over €500 per year for farmers’ use of Nitrogen fertilizers. The European Nitrogen Assessment[iv] recognizes that synthetic nitrogen fertilizers have huge advantages but also notes that their use comes with a huge price tag. The report states that the increased level of biologically active nitrogen in the biosphere might represent “the greatest single experiment in global geoengineering ever made”. For a farmer it is profitable to use nitrogen fertilizer; the return of one Euro invested in nitrogen fertil­izer is estimated at between two and five Euros. But someone else pays a bigger bill. “Environmental damage related to nitrogen effects from agriculture in the EU-27 was estimated at €20-€150 billion per year. This can be compared with a benefit of N-fertilizer for farmers of €10-€100 billion per year, with considerable uncertainty about long-term N-benefits for crop yield”.[v]

The damage caused by fertilizers includes a wide range of direct and indirect effects. Increased concentrations of nitrogen and phosphorus in the biosphere are two of the most impor­tant drivers of changes in ecosystems. Nitrogen plays a role in the formation of tropospheric ozone, which damages crops and plants.[vi] Chemical fertilizers have enabled farmers to skip sound crop rotations and to monocrop, which leads to a reduction of carbon content in soils. Globally, the discharge of nitrogen to the sea increased by 80% between 1860 and 1990. This run-off changes species composition and stimulates algal blooms and the associated dead zones.[vii]

In the United States, the Mississippi, the Columbia, and the Susquehanna rivers together discharge approxi­mately 1 million tons of nitrogen (in the form of nitrates) per year to coastal waters – about 10% of all nitrogen applied in the country.[viii] Globally, about four hundred coastal areas are now periodically or constantly oxygen-depleted as a result of fertilizer run-off, sewage discharge and the combustion of fossil fuels.[ix] The use of chemical fertilizers has also led to harmful levels of nitrates in some drinking water.[x]

Huge greenhouse gas emissions

Counting the emissions in the whole lifecycle, nitrogen fertilizers is the single biggest source of greenhouse gas emissions in agriculture. Emissions are caused by the use of fossil fuels, mostly natural gas, in the production of the fertilizers. There are emissions of carbon dioxide, laughing gas (nitrous oxide) and methane emitted in the production of fertilizers. Recent research in the US[xi] shows that methane leaks from fertilizer factories to a much larger extent than earlier estimated. There are emissions from the transportation and application of fertilizers and there are huge emissions of laughing gas from fields where artificial fertilizers are used; through denitrification, much nitrogen is lost as nitro­gen gas which in essence is harmless, but some is emitted as laughing gas, a potent greenhouse gas.[xii]

Despite this, there are no figures for the emissions from nitrogen fertilizers in the IPCC reports or national greenhouse gas inventories. The emissions are allocated to other categories and therefore they are invisible. The emissions from the production are allocated to industrial processes, the emissions from transport to transport, the emissions from application is under agriculture and the huge emissions of laughing gas from agriculture land caused by chemical fertilizers are booked under emissions from agricultural soils. But the total emissions of global use of nitrogen fertilizers corresponds to 3% of all emissions, roughly equal to global aviation emissions.

Global emissions from nitrogen fertilizers

Global consumption of N in fertilizers according to FAO is 115 million ton. For the production we can use 6 kg CO2e per kg of N, which was the European average ten years ago, most likely a bit lower than the current global average: 115*6 = 690 million ton. Note that these figures don’t include methane emissions, which according to the new US research might be substantial.

For the use phase: 115 million ton N * 1 % IPCC:s emission factor * 44/28 (this converts N to laughing gas) * 298 (IPCC factor for conversion of laughing gas to carbon dioxide equivalents): 115*1%*44/28*298 = 538 million ton for the emissions from agriculture soils caused by N-fertilizers. Adding rough estimates for transportation and application we reach somewhere above 1,400 million tons in total. Source: own calculations.

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Can we do without them?

It is often claimed that nitrogen fertilizers feed half of the world’s population. There should be no doubt about the importance of chemical fertilizers, but this figure is based on erroneous assumptions. If you just cut away fertilizers from the existing systems yields would certainly plummet, perhaps even by half, but such a scenario is not realistic. In the same way as farmers have adjusted their production to the availability of cheap fertilizers, they would make adjustments to deal with a situation without (or with less) nitrogen fertilizers. That is exactly what organic farmers do and their yields are rarely that low.

Chemical fertilizers are not (yet) essential for feeding the world or for human survival, but they are essential for the global model of commercial agricultural production. They allow farmers – even whole regions or countries – to specialize in certain crops. They also allow farmers to skip crop rotations and focus on the commercially most interesting crops. Other areas develop industrial livestock operations, based on feed bought in from the specialized crop farm areas. Chemical fertilizers also enable cities to grow without giving any thought to recycling their waste. Buying fertilizers is also consistent with the ever increasing commerciali­zation of farming. Because of the changes in production, monocropping and linear flows, pests and weeds become more prevalent, which makes farmers dependent on herbicides and biocides. In this way chemical fertilizers are one of the major building blocks of the modern food system. And the abolition or drastic reduction in the use of chemical
fertilizers is a pre-condition for a sustainable food system.

It is doable on the farm level as demonstrated by millions of farmers in all agro-ecological zones of the world. In all likelihood it is also doable in the global level. In the report, The future of food and agriculture –Alternative pathways to 2050, FAO outlines a scenario they call “towards sustainability” in which chemical fertilizers are no longer used while global food production is sufficient.


[i]Millenium Ecosystem Assessment 2005 Millennium Ecosystem Assessment: Ecosystems and human well being–synthesis World Resource Institute.

[ii]IAASTD 2009 Agriculture at a Crossroads: Global Report International Assessment of Agricultural Knowledge, Science and Technology for Development.

[iii]Liebieg,J. von. 1865 Agrikulturchemie.

[iv]European Science Foundation 2013 ‘Nitrogen in Europe, Current problems and future solutions’ part of The European Nitrogen Assessment www.nine-esf.org.


[vi]Millenium Ecosystem Assessment 2005 Millennium Ecosystem Assessment: Ecosystems and human well-being–synthesis World Resource Institute.


[viii]USDA 2013 Fertilizer Use and Price www.ers.usda.gov.

[ix]UNEP 2010 UNEP Year Book 2010: New science and developments in our changing environments United Nations Environment Programme.

[x]Millenium Ecosystem Assessment 2005 Millennium Ecosystem Assessment: Ecosystems and human well-being–synthesis World Resource Institute.

[xi]Zhou, X., Passow, F.H., Rudek, J., von Fisher, J.C., Hamburg, S.P. and Albertson, J.D., 2019. Estimation of methane emissions from the U.S. ammonia fertilizer industry using a mobile sensing approach. Elem
Sci Anth
, 7(1), p.19. DOI: http://doi.org/10.1525/elementa.358

[xii]Ayres, R. U. (editor) 1998 Eco-Restucturing: Implications for sustainable development United Nations University Press.

Gunnar Rundgren

Gunnar Rundgren has worked with most parts of the organic farm sector. He has published several books about the major social and environmental challenges of our world, food and farming.

Tags: Building resilient food and farming systems, environmental effects of industrial agriculture, nitrogen fertilizer