The Phosphorous Problem – “we are effectively addicted to phosphate rock”

In my previous post the Guardain blog entry brings to attention one of the limited natural resources that rarely gets a mention - Phosphorous! As we now know, modern agriculture is heavily reliant on fertilizers containing phosphorous, nitrogen and potassium. Phosphorous is derived from phosphate rock, which is a non renewable resource. Cordell et al. (2009) explain the phosphorous problem….

Historically crop production relied on natural levels of phosphorous in the soils. Old fashioned techniques such as crop rotation and use of manure maintained phosphorous levels for a while, however, human population soon outgrew the natural limits. Production of fertilizer moved from local, organic waste products to phosphorous material from distant sources such as guano (bird droppings deposited over previous millennia) and phosphate-rich rocks. Since the end of World War 2, global extraction of phosphate rock has tripled to meet industrial agricultures demand for NPK fertilizers.

The natural biochemical cycle recycles phosphorous back to the soil in situ via dead plant matter, whereas through modern agriculture, crops are harvested before they decompose, and transported all over the world to be consumed by humans. The phosphorous is therefore not returned to the soil directly, as human excrement is flushed into watercourses for treatment, rather than put straight back to the soils. Phosphorous is returned back to soils through annual applications of manufactured chemical fertilizers to ensure maximum yields are maintained.

Not only does our interruption of this natural cycle require copious amounts of fossil fuel-based energy, but the efficiency of the cycle is also severely reduced - 55% of phosphorous in food is lost between ‘farm and fork’ (Cordell et al 2007). Phosphorous is leached from the soil and can result in eutrophication of watercourses, this is often due to over-fertilization as chemical fertilizers contain far more phosphorous than manure.

Phosphorous flows through global food production and consumption system. (Losses and recovery are in millions of tonnes per year, Cordell et al. 2009)

Global demand for phosphorous is predicted to increase by around 3-4% annually. Reports estimate its depletion in 50-100 years. We are expected to reach peak phosphorous production in 2030 and production costs are already increasing. The quality of phosphate rock is declining therefore cheap fertilizers will soon become a thing of the past. Equally, the mining and manufacture of fertilizers is only possible when cheap fuels exist and these are rapidly running out.

90% of worldwide demand for rock phosphate is for food production. It is one of the most highly traded commodities on the international market. Only a few countries control phosphate reserves, with China having the largest. Export tariffs have recently been imposed to ensure China maintains enough phosphate to feed itself. 


There is no substitute for phosphorous in food production. One of the only viable solutions is the recovery of phosphorous, which would require a shift from importing phosphate rock to domestic production of renewable phosphorous fertilizer (potentially from human excreta). Not only would recovery of phosphorous reduce the extraction of the non-renewable resource, it would also increase countries self-sufficiency.

Cordell et al (2009) highlight “as we are learning from climate change and global water scarcity, a long time frame is required to address phosphate scarcity”. We need to take action now before peak phosphorous is reached and we have no alternative. Despite all this, phosphorous scarcity has not been addressed in the UN’s Food and Agricultural Organization official reports.

How green was the green revolution? By increasing our reliance on fertilizers, it made us addicted to phosphate rocks, which did enable many more people to survive – but for how long?