Peak phosphorous

Dr Isobel Tomlinson

25 November 2010

The supply of phosphorus from mined phosphate rock could ‘peak’ as soon as 2033, after which this non-renewable resource will become increasingly scarce and expensive. We are completely unprepared to deal with the shortages in phosphorus inputs and the hike in food prices that will follow. A radical re-think of how we farm, what we eat and how we deal with human waste – so that adequate phosphorus levels can be maintained for crop production without the use of artificial phosphate fertiliser – is crucial for ensuring future food security.

Phosphorus is an essential nutrient for all plants and animals. It forms part of genetic material, and is used for energy transfer within the cells of living things. An adequate supply of phosphorus to plants is necessary for seed formation, root development and maturation. It is second only to nitrogen as the most limiting element for plant growth and it cannot be substituted in food production.

Under natural conditions the phosphorus taken up by growing plants is returned to soils in plant residues and from the urine, excrement and carcasses of animals that have grazed the vegetation. In cultivated systems some of the phosphorus taken up by the crop is removed in harvest and then eaten directly by humans or fed to livestock. Therefore it is necessary for phosphorus to be returned to the soil in a form that is immediately available to plants, or to be stored for later release.

Historically, phosphorus was returned to agricultural land through the application of animal manure and human excreta. However, from the mid 19th century, the use of this local organic matter was replaced by phosphate mined in distant places, briefly in the form of guano (bird droppings deposited over thousand of years) but much more significantly mined rock rich in phosphate. Over the same period, as Lady Eve Balfour identified in The Living Soil (1943), the introduction into urban areas of flush toilets meant that human waste was no longer returned to the soil, but washed out into water systems.

When water-borne sewage was introduced into our cities, the capital of the soil – its fertility – which is removed from it year by year in the form of crops and livestock, no longer found its way back to the land in the form of the waste products of the community, but was poured into the sea or otherwise destroyed.
By the late 19th century, processed mineral phosphorus fertiliser from phosphate rock was routinely used in Europe and its use grew substantially in the 20th century. The production of phosphate rock increased from approximately 3 million tonnes in 1900 to 41 million tonnes by 1960, reaching current levels of around 150 million tonnes by 1980.1

Today, non-organic agriculture is dependent on regular inputs of phosphate fertilisers, derived from rock phosphate, to replenish the phosphorus lost from the soil in the process of growing and harvesting crops, and to maintain high yields. Without fertilisation from phosphorus it has been estimated that wheat yields could fall from 9 tonnes a hectare in 2000 to 4 tonnes a hectare in 2100.2

While many people are now familiar with the concept of ‘peak oil’, there is much less awareness that rock phosphate is also a non-renewable resource and that the supply is also expected to ‘peak’ in the near future. As Hubert (1956) first highlighted in relation to peak oil, it is not when a resource is completely gone that problems arise, but when the high quality, highly accessible reserves have been depleted.3 This is the point at which production reaches its maximum (its peak) and afterwards the quality of the remaining reserves is lower, they are harder to access and thus increasingly uneconomical to mine. Supply then declines and price rapidly increases. There is a growing consensus on the reality of peak phosphorus, although the exact year is, of course, not known as it depends on a variety of supply and demand-side factors where there is still some uncertainty over future trends. However, Cordell et al (2009) suggest that the peak in global phosphorus production could occur by 2033.4

Our current system of mining, using and disposing of phosphorus is not only going to be impossible when phosphate supplies peak, but is unsustainable in its current form for a number of other reasons. The sources of phosphate rock, which are highly geographically concentrated, add a further level of uncertainty in securing future phosphate supplies. In 2009, 158 million metric tones of phosphate rock were mined worldwide. Some 67% of this resource was mined in just three countries – China (35%), the USA (17%) and Western Sahara (Morocco) (15%).5 In Europe, we are dependent on imports, having no deposits of our own.

In 2007–8, the price of phosphate fertiliser increased by 800%. This has been attributed to increases in the price of oil, increased demand for fertilisers due to the increase in biofuels and the expansion of meat and dairy-based diets, and a lack of short-term supply capacity to produce enough phosphate rock to meet demand. As a result of the price spike, farmers around the world were holding back purchasing fertilisers, which partly caused the price to drop again.6 This is perhaps a taster of things to come.

Most fertiliser is produced by dissolving phosphate rock in sulphuric acid to produce phosphoric acid. For each tonne of phosphate processed in this way, five tonnes of a toxic and radioactive by-product – phosphogypsum – is produced. Greenhouse gas emissions are another consideration. The mining and production of artificial fertilisers is dependent on cheap oil supplies. As an internationally traded commodity – 30 million tonnes of phosphate rock was exported from the country where it was mined in 20087 – emissions (and pollution) from transport are also significant.

There are further environmental consequences once phosphate has been used. The process of eutrophication (the enrichment of water by nutrients) is primarily caused by phosphorus from sewerage or agriculture in rivers and other fresh-waters. Eutrophication can lead to algae growth, disrupting normal ecosystem function by using up all the oxygen in water, and causing the death of other aquatic species, and affecting water quality.

While the previous UK Government recognised that phosphorus is the key nutrient causing eutrophication in rivers and other freshwaters, the issue of peak phosphorus has been missing from all significant government policy statements on food policy and food security in the UK until recently. However, Defra’s UK Food Security Assessment (2010) recognised that phosphate rock is a geologically finite resource and, in the long-term at least, that ways to recycle phosphate in a more efficient way are needed.8 Surprisingly though there is little sense of urgency. Rather, the authors present a positive outlook for the next five to ten years. They argue that in the short to medium term the life of this finite resource should be extended through technology which can improve efficiency and thus decrease costs, as well as by exploring new offshore deposits such as those in the Pacific and Atlantic.

Indeed, it has been suggested by some scientists that market forces will lead to new technological developments that will improve the efficiency of phosphate rock extraction and that off-shore and low grade deposits will become economically viable once all high-grade reserves have been depleted.9 This may be true in the shorter term, but we should take heed at what is happening with oil; as this resource has become more scarce and more expensive to produce, so called ‘non-conventional’ resources, such as tar sands and shale oil, have become economic – with devastating environmental consequences.10 And, of course, the prices of oil and natural gas have increased. At the international level, there has been no substantial action or discussion of the issue within the international debates on global food security.

So what needs to be done? First of all, by changing what we eat we can reduce our use of phosphorus. The benefits of reducing the amount of meat in our diets in terms of health benefits and reducing greenhouse gas emissions are commonly known, but switching to a diet with less meat can also reduce the amount of phosphorus needed.

It also depends on the type of meat we eat. Livestock fed on grain fertilised by artificial fertilisers – or grazed on fields fertilised with artificial fertiliser – will be the worst offenders. Milk, butter, cream and cheese, beef and lamb from grass-fed or mainly grass-fed cattle and sheep is best. At the global level, the relative inefficiency of a meat-based diet can be understood in the context of the shift away from mixed-farming, with the effect that a significant proportion of animal manure is not returned to arable land.

We also need to change how we farm. The relative efficiency of phosphorus use in different farming systems will depend on both the levels of phosphorus inputs in the form of artificial fertilisers, animal feed, and additives in animal feed, as well as on how much phosphorus is recycled back into the system through the use of waste products. Organic farming systems already make use of many practices to reduce the need for mineral phosphate, including managing nutrient loss; using farmyard manure, crop residues and green waste composts as fertilisers; increasing the availability of phosphorus to plants by encouraging micro-organisms and mycorrizal funghi; and using crops with high uptake efficiency.

While a change in diets and a shift to organic farming systems is essential in order to completely close the phosphorus loop and minimise reliance on mined phosphate, we will need to return not only all animal waste to the soil but other types of waste as well.
It is estimated that only 0.3 million tonnes of the 3 million tonnes of phosphorus excreted by the global human population each year are returned to agricultural soils.11 In the longer term, much more human waste will need to be returned, including to land certified organic. However, a number of issues remain unresolved about the health and environmental risks of doing so.

At the present time, EU organic regulations prohibit the use of sewage sludge on organic farmland due to historical concerns about the toxic effects of heavy metals in it, caused by combining human waste with industrial effluent, domestic greywater and surface run-off.12 While heavy metal levels have declined, the presence of organic contaminants (OCs) and the risk of genetically modified organisms (GMOs) reaching the soil are additional concerns today.
There may be other ways to use human waste that would meet the high standards required by organic systems. For example, it is possible to avoid potential contamination from heavy metals and OCs through implementing ecological sanitation (ES) systems that collect and treat wastewater flows separately, optimising their potential for re-use while minimising hygienic risk. They can also reduce the high water and energy use of – and pollution caused by – the current “flush-and-forget” system. Examples include soil-based composting toilets, urine-diverting toilets and even high-tech vacuum systems.13

This is not to understate the scale of the change needed to implement ES systems. Indeed, it has been described that “the recycling of urine is a socio-technical progress that has no institutional or organisational home” and that a pervading “urine-blindness has prevented modern societies from tapping into this abundant source of plant nutrients in urine”.14 In the UK it will involve massive infrastructure developments given the extent to which urban areas are largely dependent on old centralised sewage systems.

However, there are now clear financial, political and legislative imperatives for the Government to take the lead on this issue as the problems with the current sanitary system, such as water usage and excess nutrients, become increasingly apparent and costly to deal with. Indeed, there are many areas where infrastructure changes would be more straightforward. ES systems could be made mandatory for all new housing developments. Incentives and support could be provided for retro-fitting ES systems where appropriate – for example, in rural areas where houses are not connected to centralised sewage systems and access to agricultural land would be easiest. This would be particularly useful on smallholdings and farms. Installing ES systems in public toilets and public buildings would also be excellent steps forward.

Our response to peak phosphorus requires us to focus on the interconnections between the production and distribution of our food, and the disposal of our waste. The biodiversity impacts, resource-use and greenhouse gas emissions associated with food production and distribution are all now within the sights of policy-makers. Reducing the water and energy impacts of the current sanitation system is also the subject of Government policy, as is the pollution resulting from nutrient-rich wastewater entering watercourses. What is now required is a holistic approach that offers solutions to all these problems.

Dr Isobel Tomlinson is a policy and campaigns officer at the Soil Association. You can download the full report on peak phosphorous here

End notes

1 Phosphate rock statistics form the US Geological survey available at
2 Leifert, C., Cooper, J., Wilcockson, S. and Butler, G. (2009) “The myths about sustainable high yields in conventional farming systems”, Nafferton Ecological Farming Group presentation.
3 Hubbert, M.K. (1956) Nuclear Energy and the Fossil Fuels Drilling and Production Practice American Petroleum Institute & Shell Development Co. Publication No. 95. See pages 9–11, 21–22. See
4 Cordell, D., Drangert, J., and White, S. (2009) The Story of Phosphorus: Global food security and food for thought, Global Environmental Change, 19, pages 292–305.
5 U.S. Geological Survey, Mineral Commodity Summaries January 2010 on Phosphate rock available at
6 Cordell, D. (2010) The Story of Phosphorus: Sustainability implications of global phosphorus scarcity for food security, Ph.D. thesis, Linkoping University, Sweden.
7 The International Fertiliser Industry Association (IFA) Fertiliser supply statistics available at
8 Defra (2010) UK Food Security Assessment: Detailed Analysis updated January 2010 at See page 52.
9 For example, Stewart et al 2005, as quoted in Cordell et al 2009 (page 299).
10 Greenpeace (2010) Energy Revolution, A Sustainable Energy Outlook; Friends of the Earth International (2010) Fuelling the climate crisis, undermining EU energy security and damaging development objectives.
11 Cordell et al (2009) The Story of Phosphorus, page 300.
12 EC Regulation No 889/2008 that lays down the rules for the implementation for EC Reg. No 834/2007 on organic production and labelling of organic products with regard to organic production, labelling and control.
13 Langergraber, G., and Muellegger, E. (2005) Ecological Sanitation – a way to solve global sanitation problems?, Environment International 31, pages 433–444.
14 Cordell et al (2009) The Story of Phosphorus, page 302.

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