Peak phosphorus

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Graph showing world phosphate rock production, 1900-2009, reported by US Geological Survey

Peak phosphorus is the point in time at which the maximum global phosphorus production rate is reached. Phosphorus is a scarce finite resource on earth and means of production other than mining are unavailable because of its non-gaseous environmental cycle.[1] According to some researchers, Earth's phosphorus reserves are expected to be completely depleted in 50–100 years and peak phosphorus to be reached in approximately 2030.[2][3] Whereas in stark contrast the International Fertilizer Development Center in a 2010 report estimates that global phosphate rock resources will last for several hundred years.[4] The predominant source of phosphorus comes in the form of phosphate rock and in the past guano.

Estimates of world phosphate reserves[edit]

The accurate determination of peak phosphorus is dependent on knowing the total world's phosphate reserves and the future demand for rock phosphate. Although many estimates for when peak phosphorus will occur have been made, many of them are marred by inaccurate knowledge of the quantity of world phosphate reserves. This is largely in part due to distrust in phosphate mines' reports of total reserves, with the expectation that these values will be inflated to protect their business interests. In 2012, the United States Geological Survey (USGS) estimated that phosphorus reserves worldwide are 71 billion tons, while world mining production in 2011 was 0.19 billion tons.[5] These reserve figures, although widely used for predicting future peak phosphorus, have raised concern as to their accuracy due to the fact that they aren't independently verified by the USGS.[6]

Reserves refer to the amount assumed recoverable at current market prices. Phosphorus comprises 0.1% by mass of the average rock[7] (while, for perspective, its typical concentration in vegetation is 0.03% to 0.2%),[8] and consequently there are quadrillions of tons of phosphorus in Earth's 3 * 1019 ton crust,[9] albeit at predominantly lower concentration than the deposits counted as reserves from being inventoried and cheaper to extract.

The depletion of phosphorus is very relevant to the world's food production issues. Phosphorus is a major component in fertilizer, without which fertilizer will be rendered useless. Without fertilizer, two thirds of the worlds population will starve because the Earth cannot support our demands for food.[10] There are no alternatives to phosphorus and no synthetic ways of creating it[citation needed] . According to one source, without new sources for high quality mineable phosphorus agriculture will face major problems within the next 50–100 years. According to the Global Phosphorus Research Initiative (GPRI) phosphate reserves will last 75 to 200 years[11] Therefore, exploring alternative forms of agriculture, where nutrient conservation is key, is almost certainly of vital importance.

According to the GPRI, eight to fifteen million tons of phosphorus are lost to the sea every year through run-off.[12]

Exhaustion of guano reserves[edit]

In 1609 Garcilaso de la Vega wrote the book Comentarios Reales in which he described many of the agricultural practices of the Incas prior to the arrival of the Spaniards and introduced the use of guano as a fertilizer. As Garcilaso described, the Incas near the coast harvested guano.[13] In the early 1800s Alexander von Humboldt introduced guano as a source of agricultural fertilizer to Europe after having discovered it on islands off the coast of South America. It has been reported that, at the time of its discovery, the guano on some islands was over 30 meters deep.[14] The guano had previously been used by the Mochian people as a source of fertilizer by mining it and transporting it back to Peru by boat. International commerce in guano didn't start until after 1840.[15] By the start of the 20th century guano had been nearly completely depleted and was eventually overtaken with the discovery of superphosphate.

Phosphorus conservation and recycling[edit]

A huge amount of phosphorus is transferred from the soil in one location to another as food is transported across the world, taking the phosphorus it contains with it. Once consumed by humans, it then usually ends up in local rivers via the sewage system. An example of one such crop in South America that takes up large amounts of phosphorus is soy. At the end of its journey, the phosphorus often ends up in rivers in Europe and the USA.[16]

In an effort to postpone the onset of peak phosphorus several methods of reducing and reusing phosphorus are in practice. Reducing agricultural runoff and soil erosion can slow the frequency with which farmers have to reapply phosphorus to their fields. Agricultural methods such as no-till farming, terracing, contour tilling, and the use of windbreaks have been shown to reduce the rate of phosphorus depletion from farmland. These methods are still dependent on a periodic application of phosphate rock to the soil and as such methods to recycle the lost phosphorus have also been proposed.

The oldest method of recycling phosphorus is through the use of animal and human manures. Via this method, phosphorus in the foods consumed are excreted in the manures, which are subsequently collected and reapplied to the fields. Although this method has maintained civilizations for centuries the current system of manure management is not logistically geared towards application to crop fields on a large scale. At present, manure application could not meet the phosphorus needs of large scale agriculture. Despite that, it's still the most efficient method of recycling used phosphorus and returning it to the soil. Integrated farming systems which use animal sources to supply phosphorus for crops do exist at smaller scales, and application of the system to a larger scale is a potential alternative for supplying the nutrient, although it would require significant changes to the widely adopted modern crop fertilizing methods. Alternative and far less efficient methods of recycling phosphorus have also been proposed. This includes the extraction of phosphorus rich materials such as struvite from waste processing plants.[17] The struvite can be made by adding magnesium to the waste. Some companies such as NuReSys are already using this technique to recover phosphate.

The Soil Association, the UK organic agriculture certification and pressure group, issued a report in 2010 "A Rock and a Hard Place" encouraging more recycling of phosphorus.[18] One potential solution to the shortage of phosphorus is greater recycling of human and animal wastes back into the environment.[19]

See also[edit]

Notes[edit]

  1. ^ Neset & Cordell 2011, p. 2
  2. ^ Cordell, Drangert & White 2009, p. 292
  3. ^ Lewis 2008, p. 1
  4. ^ IFDC.org - IFDC Report Indicates Adequate Phosphorus Resources, Sep-2010
  5. ^ U.S. Geological Survey Phosphate Rock
  6. ^ Gilbert 2009, pp. 716–717
  7. ^ U.S. Geological Survey Phosphorus Soil Samples
  8. ^ Abundance of Elements
  9. ^ American Geophysical Union, Fall Meeting 2007, abstract #V33A-1161. Mass and Composition of the Continental Crust
  10. ^ Pollan 2006
  11. ^ EOS magazine 9/2012
  12. ^ EOS magazine 9/2012
  13. ^ Leigh 2004, pp. 78–79
  14. ^ Skaggs 1995, p. 4
  15. ^ Skaggs 1995, p. 5
  16. ^ EOS magazine, May 2013
  17. ^ Gilbert 2009, p. 716
  18. ^ soilassociation.org - A rock and a hard place, Peak phosphorus and the threat to our food security, 2010
  19. ^ Burns 2010

References[edit]

Further reading[edit]

Rhodes, C.J. (2013) Peak Phosphorus - Peak Food? The Need to Close the Phosphorus Cycle. http://www.sciencereviews2000.co.uk/blog/view/science-progress-news/62/peak-phosphorus-peak-food-the-need-to-close-the-phosphorus-cycle/686