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Agriculture’s hunger for nitrogen oversteps planetary boundaries

Planet Earth has boundaries for its biophysical subsystems. By 2009, we had already exceeded three of the boundaries – climate change, biodiversity loss, and the nitrogen cycle. Climate change is a top-of-mind…

Overuse of nitrogen fertiliser can have nasty environmental consequences. eutrophication&hypoxia/Flickr

Planet Earth has boundaries for its biophysical subsystems. By 2009, we had already exceeded three of the boundaries – climate change, biodiversity loss, and the nitrogen cycle.

Climate change is a top-of-mind issue for governments and there has been a UN convention on biological diversity since 1993. But dramatic changes in the nitrogen cycle have received much less attention.

Humans have more than doubled the rate of atmospheric nitrogen being fixed since 1950. Fixing nitrogen makes it chemically active and therefore useful for making fertilisers and explosives.

Nitrogen is necessary, but handle with care

Fixed nitrogen is a necessary fertiliser, but its environmental impacts are serious, especially when used to excess. It contributes to environmental problems from climate change to coastal dead-zones.

Nitrogen fertiliser is vital for plant growth: plants are approximately 4% nitrogen. For this reason about 100 Mt (megatonnes) of nitrogen fertiliser is applied to crops each year. This is quite a lot of nitrogen considering that natural nitrogen fixation (from the atmospheric form to forms usable by plants and animals) is only just over double this at 225 MtN/yr.

Traditionally nitrogen fertiliser came from animal manures or guano, or nitrogen-fixing legumes. Legumes have a symbiotic relationship with bacteria in their roots that can fix nitrogen from the atmosphere.

But these natural sources of nitrogen aren’t enough to support today’s high-yielding agriculture. Almost all of our nitrogen fertilisers contain nitrogen fixed to ammonia from atmospheric nitrogen via a method called the Haber-Bosch process.

Increase in fertiliser use since the invention of the Haber-Bosch process. Trevor Garnett

The Haber-Bosch process was invented by Haber in 1909 and commercialised by Bosch in 1913. The process became particularly important during the First World War when Germany was cut off from supplies of nitrate from Chile.

The process was used in explosive manufacture during the war, but its greatest use in the past half century has been in fertiliser production.

The impact of the Haber-Bosch process on the nitrogen cycle can be seen in the nitrogen isotopes in sediments in fresh-water lakes. Humans began to affect the nitrogen cycle during the industrial revolution, through nitrogen oxides released by burning fossil fuels.

But the main change has been in the last 50 years since the green revolution in agriculture. Nitrogen fixed by the Haber-Bosch process now makes up almost half as much nitrogen input to the biosphere as natural inputs (100 Mt N/year from Haber-Bosch versus 230 Mt N/year from natural sources). Pretty much all of this has been added since the 1950s.

Environmental impacts of nitrogen in agriculture

One of the most visible impacts of nitrogen is in aquatic ecosystems. Excess nitrogen runs off into fresh water and marine environments, causing algal bloom, loss of oxygen from the water and death of aquatic animals.

Nightflyer/Wikimedia Commons

More than of $500 million worth of nitrogen fertiliser runs into the Mississippi each year. Aside from the financial loss, the nitrogen leads to phytoplankton blooms which result in major dead zones and subsequent fish kills. One such bloom recently in the Baltic Sea was half the size of Germany.

In Australia, the great Barrier Reef now receives 5.8 times more nitrogen than it did before European settlement.

Less visible are greenhouse gases resulting from nitrogen fertiliser use and misuse. Fixing nitrogen to make fertiliser is an energy-intensive process accounting for 2% of the world’s energy use. Even worse for climate change are the nitrous oxides released when excess nitrogen fertiliser is broken down by soil bacteria. These gases are 300 times more potent than CO₂ as greenhouse gases.

Steps that could reduce agricultural nitrogen use

Better targeted timing and placement: Fertilisers can be better absorbed by plants if they are applied at the right stage of growth and to the roots of plants rather than the shoots. Traditional practices - such as one application of fertiliser when seeds are sown before winter snow - are much less efficient than multiple smaller applications.

Farmers worldwide could save both money and the environment by more careful application of nitrogen fertilisers. The Food and Agriculture Organisation of the UN has looked at this problem for various regions and crops and come up with a fact sheet on how developing countries can improve soil health and use nitrogen fertiliser more efficiently.

European farmers now have to account for the nitrogen fertiliser they apply to crops, identifying what goes into plants, soils, water and so on.

The UN provides guides for more efficient use of nitrogen. IRRI

Breeding nitrogen-efficient plants: Another way of improving the efficiency of nitrogen fertiliser use is to improve the plants themselves. While considerable effort has gone into breeding crops for yield and disease resistance, little effort has been put into improving their nitrogen use, since nitrogen fertilisers have traditionally been cheap.

Researchers around the world are now working to breed plant varieties that use fertiliser more efficiently. The plants will be more efficient at both taking up nitrogen from soil and using it once it is taken up.

Understanding our nitrogen budget

Nitrogen has a long way to go to achieve the level of public awareness that problems like biodiversity loss and climate change have reached. We’re becoming used to looking at CO₂ and other greenhouse gas emissions in terms of budgets.

A similar system for nitrogen could be very useful in tracking how we’re treating this planetary boundary. A nitrogen accountability system has already started for agriculture in Europe, and could be implemented elsewhere.

What can a consumer do to make a difference? The European Nitrogen Assessment has approached this question with a video which introduces the idea of a nitrogen footprint. Like reducing your carbon footprint, it’s all about lower consumption of energy, transport, water and certain foods. This reduces the amount of nitrogen produced as a by-product of combustion processes and the amount used in agriculture if you eat foods that are more nitrogen efficient (you can achieve this at a basic level by increasing your consumption of plant foods rather than animal protein).

The nitrogen cycle has been strongly affected by human actions. The Haber-Bosch process has allowed us to increase agricultural productivity and sustain the human population at a much larger size than we could without it.

But these activities have strong effects on the environment, and crossing planetary boundaries can lead to rapid environmental change if there is a non-linear response in the earth’s systems.

The nitrogen cycle is only one of the planetary boundaries that humanity is overstepping, but it’s one we can’t afford to ignore.

Join the conversation

34 Comments sorted by

  1. Jack Heinemann

    Professor of Molecular Biology and Genetics at University of Canterbury

    Interesting article. Could you indicate what progress has been made so far through breeding low nitrogen plants? That is, what species and projected impacts on nitrogen requirements. Have any made it to commercial production yet? And what is the nature of the change leading to these traits? Is it a change in plant metabolism or the symbionts or both?

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    1. Ryan Farquharson

      Research Officer

      In reply to Jack Heinemann

      The cynic in me says we'll need to undo decades of selection and 'improvement' and going back to varieties that are able to explore the soil to get what they need. Much of our yield increases have probably been due to increases in harvest indices and reductions in root:shoot ratios made possible by the use of synthetic fertilisers.
      Also, more use of legumes is a no-brainer - using the plants themselves to fix their nitrogen powered by the sun to produce a healthier product...genius.
      And of course, as other commentors allude to, recycling what we currently flush out to sea and a little backyeard horticulture might help a bit too.

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    2. Tim Scanlon

      Debunker

      In reply to Jack Heinemann

      Legumes and other plants that use symbioses to obtain nitrogen are not competitive or don't grow as well as normal plants. They are usually used in rotation or as a constituent, rather than as a profitable crop in and of itself.

      Low N plants isn't really possible, as N is the basis of protein. You can have N efficient plants, ones that remobilise N from old leaves, etc. The bigger idea would be root exudates that allow N (and other stuff like P) to be accessed more easily in the root zone. There is work on this going on.

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    3. Trevor Garnett

      Research Fellow in Plant Physiology at University of Adelaide

      In reply to Ryan Farquharson

      Legumes are great, rotations with legumes are good practise for many reasons. However, we need high yields to be able to produce the food requirements of a large and growing human population. Growing legumes can only fix a limited amount of N and we still need fertiliser inputs for good legume yields. That rotation comes at a hit to yields of the main food crop.

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    4. Trevor Garnett

      Research Fellow in Plant Physiology at University of Adelaide

      In reply to Ryan Farquharson

      In terms of going back to old varieties, we are doing that, not using them as they are but trying to find older, less productive, varieties that may be better at taking up nitrogen from the soil. We can then incorporate these postive traits into modern more productive varieties.

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    5. Trevor Garnett

      Research Fellow in Plant Physiology at University of Adelaide

      In reply to Jack Heinemann

      There has been limited breeding for this trait, nitrogen fertiliser has always been cheap and people weren't aware of the environmental consequences. There are currently major efforts to improve nitrogen use efficiency in maize, wheat, and rice amongst other crops. A 10% increase in the efficiency of which plants can take up nitrogen from the soil would make a huge impact globally. The closest technology to commercialistion is related to modifying alanine aminotransferase, a nitrogen assimilation enzyme, in cereals.

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    6. Graham Moore

      University of Melbourne

      In reply to Ryan Farquharson

      I think Ryan makes some good points and opens an opportunity for a slightly different discussion. The ultimate reason we want to grow this food is to provide nutrition and especially proteins to people. Using leguminous crops as a direct way of getting proteins to people is a much more sustainable practice than growing crops to be used as animal feed to provide protein. One of the reasons we need the high yielding varieties is because of the vast amount of grain fed to animals. Although diets globally are changing towards more animal protein, we really need to have the debate on the sustainability of providing N and P fertilizers to support such a norm.

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  2. John Newlands

    tree changer

    Sometimes advocates for organic farming suggest compost or pea straw could be used instead of ammonia based fertilisers. If say wheat required 1 kg (probably more) dry weight of compost per square metre that's 10 tonnes per hectare. Imagine spreading that over the WA wheatbelt.

    I note the CEOs of both Dow Chemical and Incitec Pivot have cautioned against exporting too much gas as LNG. Again another fanciful idea is that wind and solar will make synthetic nitrogen fertilisers. Not at prices we're used to. As agriculture follows the Cuban model I wonder if we will be bulldozing suburbs and growing crops in beds of 'night soil'. Ah progress.

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    1. John Newton

      Author Journalist

      In reply to John Newlands

      Interesting that those with their heels dug into existing ways of doing things ridicule rather than come up with ideas to move on. Compost can be liquid, so it can be spread exactly the same way farmers now spreads herbicides that harm rather than help. Just one idea from a city bloke.

      The real problem with our society is the adversarial system where we defend positions rather than work to design solutions.

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    2. Tim Scanlon

      Debunker

      In reply to John Newton

      Compost binds nitrogen in the short to medium term. The N has to be biologically broken down by the soil bacteria to make it plant available. This is one of the issues with stubble retention and composting.

      Also composts have been shown to not work in broad-acre settings.

      Much better method is for N to be in available forms prior to the plant needing it. Fallow practices lead to this, with a 70/30 split of water/N benefit (this ratio reverses dependent upon whether the N or water is limiting post fallow).

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    3. Luke Weston

      Physicist / electronic engineer

      In reply to John Newlands

      Making ammonia (or any nitrate, which is ultimately derived from Haber-Bosch ammonia) doesn't intrinsically require any fossil fuels at all. All it requires is atmospheric nitrogen, hydrogen (from thermochemical sulfur-iodine water splitting, or any similar cycle, for example) and a heat source and energy for compression and gas transport.

      Can solar power or wind power supply the electricity (for compressors) and thermal energy on the scale required, at a viable price? Maybe. Using a fission reactor as the process heat source would certainly work.

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    4. John Newton

      Author Journalist

      In reply to Tim Scanlon

      A move forward, good. Tim - can you cite the studies re broad acre farming?

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    5. Tim Scanlon

      Debunker

      In reply to John Newton

      Not technically allowed to. I've seen the data but it is owned by a private group. They might publish it with GRDC or with Crop Updates next year. Usually though, these studies just disappear because the guys selling the stuff bury the results.

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  3. Yoron Hamber

    Thinking

    What happens with the extra nitrogen in the air? What is their atmospheric time? And where do they end.

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    1. Trevor Garnett

      Research Fellow in Plant Physiology at University of Adelaide

      In reply to Yoron Hamber

      Nitrogen makes up 78% of the air we breathe, however it is not fixed, that is the point of this discussion, this fixed and reactive oxygen is a major manipulation to the atmosphere and we don't really know the consequences of what this input will be.

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    2. Michael Hay

      retired

      In reply to Yoron Hamber

      There is nothing new under the sun - 17th century farmers in Europe knew the value of rotational cropping and stocking. Australia's problem began with the 'grazing' mentality; bare the land in one place, them move on, in full realization that there is plenty of fresh land ahead.
      Australia has good farmers; it is just a pity that not enough of them have studied the art of farming - there is plenty of knowledge in the Agricultural Universities both here and world-wide to lift the farming practices.
      Knowledge is a wonderful thing ; practice alone does not necessarily make perfect.

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  4. Graham Moore

    University of Melbourne

    Some interesting aspects of the N cycle have been put in perspective by this article. In terms of plant nutrient issues, while we cannot afford to ignore the issues raised with the N cycle, at least there is a cycle. I am much much more concerned about the P (Phosphorous) non-cycle which starts in a mine in Morocco, China or the US and ends up being flushed down our toilets into the oceans. At least the N cycle is vaguely closed with N returning to the atmosphere from soil and waste water treatment…

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  5. Eric Ireland

    student

    Controlled release fertilisers, nitrification inhibitors and urease inhibitors could also be used to reduce losses of fertiliser nitrogen. It probably isn't economical at the moment but if we start pricing the cost of nitrous oxide emissions, it could be. http://dx.doi.org/10.1071/SR07197

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  6. Gerard Wedderburn-Bisshop

    logged in via email @worldpreservationfoundation.org

    Great to hear some discussion on nitrogen imbalance - overstepping this planetary boundary is one of the greatest threats to all life on earth

    Of course nitrogen is critical for protein building - gross nitrogen content is the first-level test for protein content, but we have fixed so much of it with the Haber-Bosch process we are running an experiment in pollution that will test our systems to failure.

    What is missing from this article is that animals (including us) act as nitrogen concentrators…

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  7. Peter Fox

    Medical doctor

    All you are saying is give peas a chance?

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  8. Wade Macdonald

    Technician

    I would like to get feedback from the authors as to why the Australian Government veto'd this product linked below while the rest of the world embraces it?

    I hope it wasn't because the chemical fertiliser industry has too much political influence?

    Are we all suffering because good alternatives that save our lands, coasts and oceans get ignored?

    http://anthillonline.com/making-plants-happy-lands-geomite-biomineral-second-place-in-anthills-smart-100-2/

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    1. Tim Scanlon

      Debunker

      In reply to Wade Macdonald

      In all honesty, that product sounds like pseudoscience rubbish. Be wary of anything that mentions "biodynamic farming" because it is likely to be rubbish. Biodynamics is the homoeopathy of the agriculture world.

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    2. Wade Macdonald

      Technician

      In reply to Tim Scanlon

      No probs thanks Tim,

      I have heard that trials overseas were going well post the info on that link and thought I would seek the authors views as to the validity of the product and Government stance.

      As a fisher I have seen what high nutrient levels have done to rivers, lakes and estuaries and would love to see some big developements to rectify the problem.

      Cheers

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    3. Tim Scanlon

      Debunker

      In reply to Wade Macdonald

      I couldn't find any real evidence for his claims. He is also making some big claims that would appear to be opposing natures of the product. To quote: "combined fertiliser, soil ameliorant, carbon creator and structural builder" seems an odd thing to say. If it is a carbon creator, does he mean the fertiliser grows roots that store a bit of carbon (for a year or two before they are broken down) or does he mean as a provider. Biochar isn't a fertiliser, yet he seems to think it is. Fertiliser and ameliorant seems unlikely, as the chemistry is not necessarily compatible, depending upon what it is that it provides.

      Basically, he could be onto something, but it just seems really unlikely, especially when you consider the lack of actual evidence and explanation. Affiliation with biodynamics just makes me think that this is just empty claims.

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    4. Trevor Garnett

      Research Fellow in Plant Physiology at University of Adelaide

      In reply to Wade Macdonald

      There are many alternative products out their, many have good aspects but all really need to be tested properly before they can be recommended. This particular product appears to require carbon to be imported to Australia from another country, how sustainable is that? Is is any different from exporting phosporous from Nauru?

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    5. Wade Macdonald

      Technician

      In reply to Tim Scanlon

      Yeah,

      I couldn't find the info I saw earlier this year on this product either, other than from the horses mouth.

      Save alot of biodiversity if we could reduce the need for chemical fertilisers.

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    6. Tim Scanlon

      Debunker

      In reply to Graham Moore

      Like a lot of those "trials", I doubt anything will ever surface. I know of several "trials" of products that were thought to be or known to be snake oil, they quietly disappeared after they had done their publicity tour.

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  9. Tim Scanlon

    Debunker

    One issue that wasn't covered in this article that is of concern is the loss of N to volatilisation. This is an issue for both soil and fertiliser sources of N. There are some huge losses in N that occur from volatilisation that should be limited more than they currently are.

    I'd like to see perennials used to address many of these issues. A perennial staple crop (e.g. wheat) would mean only planting once every few years, rather than annually. This would allow for deeper root systems which would stop/limit N leaching, allow better soil exploration (efficiency) and plant activity could be for a larger proportion of the year, so out of season rain and N mobilisation would be taken advantage of.

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  10. Shaun King

    Designer

    I've been a backyard farmer for 20-30 years now. Never claiming to be organic, biodynamic or thermodynamic or whatever.

    A gardener, or food grower, follows a simple principle. You want you garden bed to be in better condition next year as it was this year. Simple logic that sustained indigenous communities for thousands and thousands of years on the land.

    With a little reading you soon learn that the packaged fertilisers are not going to give you that result. So, I personally use a mixture…

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  11. Alex Cannara

    logged in via LinkedIn

    Good piece. In Calif., we've dealt with nitrate production from vehicles polluting alpine lakes int eh Sierra Nevada, thus our requirements for ctlytic converters that do more than just reduce hydrocarbon & CO emissions.

    Also, overuse of nitrate fertilizers worldwide creates the new ozone killer -- NxOy, some of which are natural products of soil bacteria given too much fixed N. And, N2O is over 100 times the GHG that CO2 is.

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  12. Julian de Ross

    Company Director

    I guess humanity has become too many... let's cull a few million..beginning with Greens and other extremists.
    -Peta
    -Animal Lib

    Or.. just continue using the 'Global Warming' card to justify massive wealth redistribution to poor countries.
    Never mind about addressing the contractual arrangements between our privatized power providers which limit how much Solar energy that can be allowed to the Grid.. we wouldn't want to slash their profits now would we ?

    The Starting point of any serious approach to stopping "Global Warming" is forcing government to change the contracts, withOUT compensation, and ramping up the fitout of Solar on rooftops. It's actually affordable now through group buying plans. We should fix ourselves before worrying about Hose' in Mexico.

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