Can We Feed the World?

Is There a Nitrogen Limit of Food Production?

© 2005 Dr Ron Nielsen

IN PLAIN ENGLISH (for those who like it short and simple)

Nitrogen is a vital and important ingredient of living organisms. Without nitrogen there would be no life on earth, or at least not a life as we know it. The atmosphere is made mainly of nitrogen so there is more than enough of it to support life. But it is like with water, like being in the middle of an ocean and having not a drop to drink.

Nitrogen atoms in the atmosphere come in pairs. As long as they remain in this form they cannot be used by living organisms. They have to be pulled apart. However, the bond between them is so strong that they remain undisturbed.

Lightening can break the bond but they do not produce sufficient quantities of the biologically reactive nitrogen to be of any substantial use. Thus nitrogen as it is present in the atmosphere remains useless for the living organisms. So how do we and other living organisms survive in this apparently unfriendly and uncooperative environment.

There must be something in nature that can break the bond between two nitrogens and free them. There must be something that converts the biologically useless nitrogen into useful forms. This process of turning useless nitrogen into useful forms is called nitrogen fixing.

Fortunately for the life on earth, there is a small group of microorganisms that can do the job very nicely and efficiently, thank you very much. It's really marvelous! What a lightening does with a big bang and with a huge discharge of energy, these tiny microorganisms do the same without fuss. They can take the biologically useless nitrogen from the atmosphere, break it apart, and convert it to nitrogen compounds that can be used by other living organisms. Isn't it a clever solution.

When I think about it, I wonder whether there might be a similar solution to the nuclear fusion energy but we don't know about it. But this takes us to an entirely different topic. So let's return to nitrogen.

Until not so long ago, only nature could fix nitrogen but now we also can do it. We do not have to rely on nature anymore. We can fix nitrogen, produce nitrogen-based fertilisers, and increase food production.

Unfortunately, our shortcut didn't turn out to be as fortunate as we hoped for. We have to use more and more fertilisers, and human-created nitrogen pollution increases so rapidly that by 2050, the whole globe will be strongly polluted. Nitrogen pollution is deadly. It suffocates aquatic animals, it is harmful to humans, and destructive to biodiversity.

Do we have to use nitrogen-based fertilisers to produce food?

In this article I challenge two claims: (1) that the human-invented process of fixing nitrogen caused global population explosion, and (2) that without nitrogen-based fertilisers we would not be able to feed the world.

I show that the population explosion was already advanced and well on the way when nitrogen-based fertilisers were introduced. The use of fertilisers may have supported the already present population explosion, but even this is doubtful. It is quite possible that the explosion would have continued even if we didn't boost food production with nitrogen-based fertilisers. However, what is certain is that the use of fertilisers did not cause global population explosion.

I also argue that we could feed the world without using nitrogen-based fertilisers. Fertilisers might make it easier to produce food but this does not mean that they are essential. Considering their harmful effect, their use may be regarded as counterproductive. In fact, after a short initial improvement, human wellbeing plummeted because of the use of nitrogen-containing fertilisers. Their alleged beneficial function in food production is no longer so obvious. They appear to be now a curse rather than a blessing.

In the production of food, nitrogen-based fertiliser play a similar role as fossil fuels in the production of energy. They give a quick fix but they cause a long-lasting harm. They destroy soil productivity, destroy the aquatic life (and thus destroy this food source), kill land animals, destroy plants, and kill people.

We should look for solutions in a prudent organic farming, in improving irrigation efficiency, in improving the environment for nitrogen-fixing organisms, in healing the soil, which we have destroyed by using nitrogen-based fertilisers and other agricultural chemicals, and in changing our food consumption habits. The last area might not be appealing, but we should remember that by consuming animal food we consume recycled nutrients. It takes, for instance, many kilograms of plant matter to produce one kilogram of beef. It would be all right, for instance, if cows ate only grass, but we also feed them with perfectly good grain, which we could use more efficiently as our direct source of food.


The important ingredient of life is nitrogen and we cannot live without it. This element contributes only 1-4 per cent to the dry weight of plants (Raven, Evert, and Eichorn 1986) but is an essential nutrient . It is a component of the fundamental life-related molecules such as the genetic code (DNA) and amino acids, which are the building blocks of proteins (including of course enzymes, which are essential in supporting numerous metabolic reactions).

Unfortunately, the problem with nitrogen is similar to the problem with water. The surface of our planet is made mainly of water but we cannot use it because it is salty. The atmosphere is made mainly of nitrogen but, in general, living organisms cannot make use of it.

Atmospheric nitrogen is made of two nitrogen atoms bound so strongly that it is hard to break them apart. To make it usable it has to be “fixed”, that is, converted to biologically active forms. Lightning carries enough energy to break the nitrogen molecule apart but it produces only small amounts of the reactive nitrogen. Fortunately, certain small group of micro-organisms in the soil and water have the ability of fixing nitrogen. If not for them, life on Earth, as we know it would not exist.


The frequently quoted claim is that we have to use nitrogen-based synthetic fertilisers to produce food because we do not have enough of naturally produced reactive nitrogen. According to this claim, traditional farming methods can produce food for only about 60% of global population (Smil 1997 and 2001) or to about 4 billion people.

A related claim is that synthetic nitrogen-based fertilisers caused global population explosion (Smil 1999). This claim is relatively easy to check but it finds no convincing support in the demographic data.

The dependence of global population on time can be described remarkably well using a simple mathematical function (Nielsen 2005). As discussed in my book, the beginning of the population explosion can be traced to the early 1800s but the intensive production and use of nitrogen-based synthetic fertilisers commenced around 1950, or more than 100 years later. The introduction of synthetic fertilisers had no significant effect on the demographic data and on their mathematical representation (see Figure 1).

The buildup of the population explosion has commenced at least around 500 AD and has been progressing at a steady pace until the mid 1300s. From around 1400, the pace increased slightly and continued until the end of the 20th century. These dates have nothing whatever to do with the production and use of synthetic fertilisers. (Plots showing these dates will be presented in a separate article at a later date.)

Considering the lack of evidence for the nitrogen-related explanation of the population explosion, the claim that there is not enough of the naturally produced reactive nitrogen to feed the world deserves reexamination.

Figure 1: Global Population

This plot shows that the introduction of synthetic fertilisers had no dramatic effect on the increase of global population, which was already underway since at least 500AD and which exploded in the early 1800s. Global population data follow closely a simple mathematical function (hyperbola). The fertiliser hypothesis is a myth that has no confirmation in the demographic data. It is one of the attractive fictions that unfortunately is repeated even in respectful publications.

Source: My calculations as discussed in my book (Nielsen 2005).


In 1918, Fritz Huber received Nobel Prize for his breakthrough discovery of a shortcut to the production of the reactive nitrogen. He has found a way for a synthesis of ammonia directly from nitrogen and hydrogen under high pressure and in the presence of a catalyst. To make this method commercially available, Carl Bosch contributed his technical expertise, and the commercial production of ammonia began in 1913. About 80% of ammonia is now used in the production of nitrogen-based fertilisers.

Synthetic fertilizers boosted food production and increased people's health and wellbeing. However, after an initial rapid improvement, came a swift decline because the problems created by the use of synthetic fertilisers outnumbered their benefits (Townsend et al. 2003). The use of fossil fuels, which also contribute to the production of the reactive nitrogen, added to the problems created by the use of synthetic fertilisers.

Human Health

Figure 2: Nitrogen and human health

A conceptual diagram by Townsend et al. (2003). This picture tells a said story of the initial euphoria followed by a despair caused by the human interference with nature. We are now in a nitrogen trap and we do not know how to get out of it.

Bleu curve Human-assisted fixation of nitrogen boosted food production (the rising side of this curve). However, after the initial success came disappointment because the increase in crop yields slowed down (the leveling off part of the blue curve). We use increasingly more nitrogen but we are not rewarded by a proportional increase in food production.

Black curve (the left-hand side) — With more food being initially available, human wellbeing and health improved.

Red curve However, nitrogen pollution also increased, slowly at first but then much more rapidly.

Black curve (the right-hand side) — The rapidly increasing nitrogen pollution and the small increase in crop yields caused a rapid decline in the human wellbeing and health.

We already have too much of the harmful nitrogen in the environment but human health benefits are low. Nitrogen pollution is increasing rapidly and human wellbeing is equally rapidly decreasing. However, we have to produce more food to feed the ever-increasing human population. How to break the spell and find a way out of this vicious circle?

Source: Townsend et al. 2003. (See also the website source: The North American Nitrogen Center, Bob Howarth, Director, Alan Townsend, Associate Director.) Reproduced with kind permission of Bob Howarth.


Nitrogen contributes to the nutrient pollution (eutrophication) of aquatic ecosystems. The resulting overproduction of organic matter, such as algae, reduces dissolved oxygen and causes suffocation (hypoxia) of aquatic animal life. In addition, the growing algae produce toxins.

Eutrophication occurs in lakes, rivers, and dams near farmlands and in many coastal areas near the outlets of rivers. Marine eutrophication is a serious problem in many coastal regions of North America, Europe, and Japan. It also occurs in Australia and New Zealand (Bowman and van Vuuren 1999; UNDP et al. 2000).

Excessive use of nitrogen reduces soil fertility, promotes weed growth, and increases the risk of pests and agricultural diseases (Matson et al. 1997). It also affects human health through air and water pollution. It causes reactive airways disease, respiratory tract inflammation, compromises immune system, increases allergic responses, causes reproductive problems, methemoglobinemia (excess of useless form of haemoglobin containing triply charged iron that cannot carry oxygen), and cancer. It contributes to greenhouse effect, acid deposition, particulate pollution of the troposphere, decreased ecosystem biodiversity, and promotes the spread of disease carrying organisms (Cowling et al. 2002; Galloway et al. 2004; Mosier, Syers, and Freney 2004; Socolow 1999; Towensend, et al. 2003).


Reactive nitrogen comes now from a variety of sources: the unassisted natural biological fixation, human-assisted natural biological fixation (legume crops and green manures), lightning, Haber-Bosch synthesis (used mainly to produce nitrogen fertilisers), and from the combustion of fossil fuels (see the figure below).

BNF-terrestrial (terrestrial biological nitrogen fixation) The natural production by terrestrial micro-organisms decreased from 120 teragrams (trillion grams) per year [Tg/y] in 1860 to 107 Tg/y in the early 1990, and is projected to decrease to 98 Tg/y in 2050 (Galloway, et al. 2004). This is a said but hardly surprising outcome. It would certainly be better for us if nature did the work for us. We could then reduce the use of synthetic nitrogen fertilisers and thus reduce the pollution. However, we destroy the land and vegetation, and we soak the soil with harmful agrochemicals. No wonder that the useful micro-organisms have now little chance to survive and do their work.

The reactive nitrogen is also produced in the marine environment at 121 Tg/y. Its production remains constant.

Lightning — Contribution from lightning remains constant at about 5.4 [Tg/y].

BNF-cultivation (biological nitrogen fixation by bacteria living in the roots of skillfully selected plants by farmers) — Skillful cultivation increased the biological fixation of nitrogen from 15 Tg/y in 1860 to 31.5 Tg/y in the early 1990s. The projected value for 2050 is 50 Tg/y. BNF-cultivation just manages to compensate for the loss in BNF-terrestrial.

Fossil fuels —Reactive nitrogen pollution from fossil fuels was 24.5 Tg/y in the early 1990s and is projected to increase to 52.2 Tg/y in 2050.

Haber-Bosch (synthetic fixation of nitrogen by using the Haber-Bosch process) — From around 1950, the production of harmful nitrogen increased rapidly mainly in the form of the synthetic fertilisers. Haber-Bosch synthesis produced 100 Tg/y of the reactive nitrogen in the early 1990s, which was nearly the same as the amount produced by the natural biological fixation (BNF-terrestrial). The projected value for the Haber-Bosch production in 2050 is 165 Tg/y, which will be nearly 70% larger than the natural production of nitrogen (BNF-terrestrial).

Nitrogen Production

Figure 3: The rapidly increasing production of the reactive nitrogen

I have constructed this graph using the numerical data published by Galloway et al. (2004) and the graphs in Cowling et al. (2002).

The natural biological production of the reactive nitrogen (BNF-terrestrial) is decreasing but is compensated by the human assisted biological fixation (BNF-cultivation). The largest contribution to the environmental pollution by nitrogen comes from the Haber-Bosch synthesis, most of which supports the production of nitrogen-based synthetic fertilisers.

Human assisted production of the reactive nitrogen is now (in 2005) around 194 Tg/y. This includes not only nitrogen generated by fossil fuels (27 Tg/y) and the Haber-Bosch synthesis (128 Tg/y) but also the human assisted biological fixation (BNF-cultivation). Human contribution is therefore about 13 times greater than in 1860. By 2050, human assisted production of the reactive nitrogen will increase to 267 Tg/y and it will be nearly 18 times higher than in 1860. In that year, the total biologically produced nitrogen in terrestrial ecosystems (including the cultivation-assisted fixation) will be 148 Tg/y but the total produced by the Haber-Bosch synthesis and fossil fuels will be 217.2 Tg/y or nearly 50% higher than the combined natural terrestrial production.

The problem with the overproduction of the reactive nitrogen is that only a small amount of it is consumed as food. Most of it is released to the environment where it causes enormous damage.


Nitrogen deposition all over the globe, not only over the land but also over the oceans. By the early 1990s, nitrogen pollution was strong in the US, parts of South America, Europe, India, and China. By 2050, the nitrogen cancer is projected to spread over larger areas and engulf nearly all the Earth.

1860 nitrogen depositions
The early 1990s nitrogen depositions
2050 nitrogen depositions
The early 1990s

Global nitrogen depositions in 1860, the early 1990s, and 2050
(Link to a larger version of these maps.)

Source: Galloway et al. 2004. (See also International Nitrogen Initiative). Reproduced with kind permission of Jim Galloway.


A claim that the production of synthetic fertilisers caused global population explosion is not supported by the demographic data. Introduction of synthetic fertilisers and the associated initial increase in food production shows no clear influence on the global population explosion. The explosion was already well developed and the data follow closely undistorted mathematical function. This function has nothing to do with the introduction of synthetic fertilisers but it describes global population explosion remarkably well.

This absence of a clearly visible influence of synthetic fertilisers on the trend of global population puts also in doubt a claim that synthetic fertilisers play a vital role in food production. There is no doubt that initially they have made food production easier but this does not mean that they are essential.

Food is not the only requirement to increase human wellbeing. We now have strong evidence that while the use of synthetic fertilisers increases food production levels off and human wellbeing decreases. The use of synthetic fertilisers creates more problems than it solves. They are more harmful than beneficial.

Much of the nitrogen used in fertilisers is released to the environment. Only about 14 per cent is consumed in the form of plant-based diet and about 4 per cent in the form of meat diet. Worldwide, about one-third of harvested grain is also used as livestock feed (UNDP et al. 2000). In the US the fraction is even higher, about 50 per cent. Nourishing food, such as corn, is also converted to dispensable products such as commercial sweeteners (Howarth et al. 2002).

There appears to be an urgent need to eliminate to use of nitrogen-based fertilisers. We should look for solutions in traditional farming. We should work on cleaning the waterways and restoring soil integrity, which we destroyed by the use of artificial fertilisers and agricultural chemicals. We have to consider changing our eating habits. A shift to plant-based diet would help in reducing nitrogen pollution. During the transition period, while we are developing safer farming methods, we should look for more efficient ways of using synthetic fertilisers (Howarth et al. 2002).

Various solutions to nitrogen and food production problems have been suggested, including genetic engineering to improve natural production of the reactive nitrogen (Cowling et al. 2002; Mosier, Syers, and Freney 2004; Smil 1997; Socolow 1999). Generous investment in restoring the environment is necessary if we want to reduce our dependence on synthetic fertilisers.

There is no single solution but rather a series of solutions that could help to reduce and eventually to eliminate the need to use the synthetic fertilisers and to clean the harmful pollution they are causing worldwide. To find and apply the needed solutions requires a combined effort of primary food producers, scientists, engineers, policy makers, and the public.

(See for instance Cowling et al 2002.)

The biologically reactive nitrogen (also known as reactive nitrogen) is made of various groups. It includes inorganic reduced nitrogen (such as NH3 and NH4+); inorganic oxidised nitrogen (such as. NOx, HNO3, N2O, NO3-, and NO2-) and organic compounds (such as urea, amino acids, amines, proteins, and nucleic acids).

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You may use the information contained in this article as long as you refer to it as Nielsen, R. 2005, 'Can We Feed the World? The nitrogen limit of food production', If you wish to use the diagrams from external sources, please contact their authors.


For information about all critical global trends shaping our planet's future see my book: The Little Green Handbook: A guide to critical global trends.


Bowman, A. F. and van Vuuren, D. P. 1999, Global Assessment of Acidification and Eutrophication of Natural Ecosystems, UNEDP, Nairobi, Kenya (UNEDP/DEIA&EW/TR.99–6) and RIVM, Bilthoven, The Netherlands (RIVM 402001012).

Cowling, E., Galloway, J., Furiness, C., and Erisman, J. W. (eds) 2002, Optimising Nitrogen Management in Food and Energy Production and Environmental Protection, Report from the Second International Nitrogen Conference, Potomac, MA, 14-18 October 2001, The Ecological Society of America, Washington, DC.

Galloway, J. N., Dentener, F. J., Capogne, D. G., Boyer, E. W., Howarth, R. W., Seitzinger, S. P., Asner, G. P., Cleveland, C., Green, P., Holland, E., Karl, D. M., Michaels, A. F., Porter, J. H., Townsend, A. R., and Vörösmarty, C. 2004, ‘Nitrogen Cycles: Past, present, and future’, Biochemistry 70:153-226.

Howarth, R. W., Boyer, E. W., Pabich, W. J., and Galloway, J. N. 2002, ‘Nitrogen Use in the United States from 1961–2000 and Potential Future Trends’ Ambio 31:88-96.

Matson, P. A., Parton, W. J., Power, A. G., and Swift, M. J. 1997, ‘Agricultural Intensification and Ecosystem Properties’, Science 277:504-508.

Mosier, A. R., Syers, J. K., and Freney, J. R. (eds) 2004, Agriculture and the Nitrogen Cycle: Assessing the impacts of fertilizer use on food production and the environment, Island Press, Washington DC.

Nielsen, R. 2005, The Little Green Handbook: A guide to critical global trends, Scribe Publications, Melbourne, Australia.

Raven, P. H., Evert, R. E., and Eichorn, S. E. 1986, Biology of Plants, 4th edn, Worth Publishers, New York.

Smil, V. 1997, ‘Global Population and the Nitrogen Cycle’, Scientific American 277:76-81.

Smil, V. 1999, 'Detonator of the Population Explosion', Nature, 400:415.

Smil, V. 2001, Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of Food Production, MIT Press, Cambridge (MA).

Socolow, R. H. 1999, ‘Nitrogen Management and the Future of Food: Lessons from the management of energy and carbon’, Proc. Natl Acad. Sci. USA 96:6001-6008.

Townsend, A. R., Howarth, R. W., Bazzaz, F. A., Booth, M. S., Cleveland, C. C., Collinge, S. K., Dobson, A. P., Epstein, P. R., Holland, E. A., Keeney, D. R., Mallin, M. A., Rogers, C. A., Wayne, P., and Wolfe, A. H. 2003, ‘Human Health Effects of a Changing Global Nitrogen Cycle’, Ecol. Environ. 1(5):240-246.

UNDP, UNEP, WB, and WRI 2000, World Resources 2000–2001: People and the fraying web of life, Oxford University Press, New York, US.