tractor running over a crop

Peak phosphorus—will humanity run out of a critical resource?

We might have enough phosphate rock or we might not. It depends on who you ask.

Global fertiliser use in 2021 was 266 million tons.

That is the estimate of the FAO report on World fertiliser trends and outlook to 2022 for ammonia, phosphoric acid and potash combined. 

266 million tons is a meaningless number on its own. 

For some context, a typical medium-sized bulk cargo ship used to transport fertiliser has a displacement of 50,000 tons, so we are talking about 5,320 shiploads of the stuff.

That’s a lot of ships.

Photo by Chris Pagan on Unsplash

In 24 hours a large cargo ship can travel 1,000 km and will consume 280,000 liters of fuel.

Most people think of nitrogen as essential for plant growth, and it is, but phosphorus is critical too, especially in food root crops. It is vital for cell division, especially for seedlings and young plants. Adding phosphorus to soil promotes root growth and winter hardiness, stimulates tillering, and can speed up plant maturity.

Phosphate rock minerals are the only significant global phosphorus resource for use in agriculture. 

It used to be guano—accumulated bird and bat poo—full of nitrogen, phosphate and potassium. In the 19th-century, the guano trade played a pivotal role in the development of modern input-intensive farming. The high demand led the United States to pass the Guano Islands Act in 1856, which gave U.S. citizens who discovered a source of guano on an unclaimed island exclusive rights over the deposits. Have to love arrogance?

gannets perched on a rock with streaks of white guano
Photo by Kristina Hoeppner on Unsplash

By 1846, 462,057 tonnes of guano had been exported from Ichabod Island, off the coast of Namibia, and surrounding islands, to Great Britain.

Once the German chemists Fritz Haber and Carl Bosch figured out an industrial method to artificially fix nitrogen in ammonium in the early 1900s, bird droppings became less popular. It was easy enough to process rock phosphate and add it to the ammonium as a critical ingredient in many inorganic fertilisers. 

Today, global agriculture relies on rock phosphate, with 220 million tons used in 2021. Hence, a shortage or just significant price increases could negatively affect the world’s food security.

Initially, there was a concern. 

Researchers estimated that the Earth’s commercial and affordable phosphorus reserves could be depleted in 50–100 years, reaching peak phosphorus in approximately 2030. 

Others suggested that supplies would last for several hundreds of years. The International Fertilizer Development Center, IFDC, estimated that worldwide phosphate reserves are around 60 billion metric tons of concentrate. In addition, the IFDC estimate of global phosphate rock resources is approximately 290 billion metric tons, which includes the unprocessed ore of the reserve estimates. 

But we would expect a bullish projection from a fertiliser development NGO.

Sources of phosphate rock

Where the phosphate rock comes from is as important as the volume. 

USGA reported global phosphate rock production in 2021 of 220 million metric tons which included 85 MMT from China and 38 MMT from Morocco. They also reported a lower global estimate of 71 billion metric tons of phosphate rock reserves, but this is still over 300 years of supply at the 2021 rate of extraction.

If China moved to choke supply, it would be catastrophic, as would a problem in Morocco, given between them, they make half the total volume. 

Such geographic concentration is a risk.

oasis in the western sahara desert
Photo by Sergey Pesterev on Unsplash

Morocco has occupied the disputed region of Western Sahara since 1975. If this region is added to reserves in Morocco proper it amounts to 72% of all phosphate-rock reserves in the world.

So no peak phosphorus. 

It would seem that there is time for all manner of disasters to befall humanity before we run out of phosphate rock. The resource exists.

The challenge is more about the accessibility of these reserves. How easy will it be to dig them out of the ground and how costly? Not to mention the geopolitics of a resource crucial to feeding everyone.

If the rock can be mined, processed, and distributed at close to current costs, stocks and flows can be maintained. If the cost of extraction goes up, the price must too or miners and processors go out of business and supply tanks.

And the demand is climbing as agricultural intensification spreads and depleted soils require more fertiliser than ever to maintain crop yields.

graph that show the rise in phosphate rock production from 1910 to 2010

Graph by StefanPohl – Own work, CC0,

No peak phosphorus perhaps, but there is still sovereign risk, not to mention the disruption should supply chain delays affect a proportion of those 5,000+ shiploads.

Even when reserves are healthy, supply might not be. 

What sustainably FED suggests

Humanity has exploded since the early 1900s, adding 6 billion souls in a little over 120 years. 

We took the free energy from fossil fuels and, via industrial agriculture, turned it into people plus the infrastructure and economic activity to meet their needs. All this success means we are bumping into planetary boundaries and overshooting several of them. 

Typically these boundaries are described as an innate capacity as though the planet has resources for humans to exploit as we obey the biblical edict and subdue the earth.

Phosphorus is an example of a planetary boundary that we created for ourselves. Access to phosphorus for fertilisers is now essential to keep 7.8 billion people fed—recall the daily human energy demand from food is 22 trillion calories.

Resource limits like this that previously we couldn’t imagine will appear all the time. Just one of the consequences of dominion. 

Science sources 

Cordell, D., Drangert, J. O., & White, S. (2009). The story of phosphorus: global food security and food for thought. Global environmental change, 19(2), 292-305.

Hero image from photo by James Baltz on Unsplash


Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

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