October 18, 2011

Time to Rethink Our P?

Jared Margulies, MS

Jared Margulies, MS

Guest Blogger

Center for a Livable Future

Much of the world's phosphate is in the Western Sahara

Here’s a riddle: What is essential to all life on earth, is thrown away instead of recycled, is quickly running out on a global scale, and yet has no substitute?

If you guessed fresh water, you wouldn’t be wrong. But would you have guessed phosphorus?

Despite growing acceptance in the scientific community of peak oil as a legitimate cause for concern—and perhaps a bit more attention from the media—far less attention has been paid to the phenomenon dubbed “peak phosphorus,” despite increasing evidence that peak phosphorus is expected to occur by 2030, if it hasn’t already.

Phosphorus (P) is an essential element for all biological life—it is a key element of DNA, RNA, ATP (think cellular energy), and bones.  Beyond being necessary for life, it is essential for crop (food) production. Today, phosphate rock is processed into P fertilizers, which are applied at rates ranging from 3 kilograms per hectare (kg/ha) in Africa to 25 kg/ha in some places in Europe, with a global average application rate of 10 kg/ha. While most of the U.S. supply of P fertilizer is still produced domestically, our reserves are expected to be exhausted in a few decades.*

Elemental phosphorus is unstable, and does not exist in the presence of oxygen; it largely exists in the form of phosphates, locked up in mineral deposits (i.e. rocks) formed over geologic time. Today, a small number of countries mine the vast majority of phosphate rock—outside phosphate mining in the U.S. and China, which is almost exclusively for domestic use, the contested lands of the Western Sahara mined by Morocco make up one the world’s largest known phosphate deposits as reported by e360 earlier this year.**

Because there are no substitutes for phosphorus in the agricultural system, peak phosphorus is even more worrisome than peak oil, in many respects. Industrial agriculture, characterized by intensive use of fertilizer, is heavily dependent on P fertilizers for maintaining high agricultural yields.  The rapid depletion of global phosphorus resources now has scientists and governments worried about how to meet agricultural yield demands (as world population crests 7 billion this month) in the coming decades in the era of peak phosphorus.

But this isn’t a problem without solutions.  While our current food production system heavily relies on phosphorus, we waste huge amounts of it in animal and human wastes, which, due in part to lax environmental regulations, are allowed to enter our waterways in huge quantities. When excess phosphorus enters our waterways via animal and human wastes, the result can be algal blooms and eutrophication.*** The environmental impacts on our aquatic and marine ecosystems can be devastating.

As Childers and colleagues have argued in a paper this year in BioScience, there are critical and necessary steps we can take to “close” the human and animal production P cycles. Closing these P loops necessitate safely recycling human and animal wastes back into the agriculture production system, rather than allowing finite P resources to literally wash away. In agricultural systems, this means managing waste applications to fields more effectively to reduce runoff and erosion events, and also a reconsideration of our current industrial food animal production system, which concentrates animal production to such a degree that particular regions and landscapes are overburdened with excessive animal wastes resulting in unnecessary P losses.

As individuals, one effort we can all make to help achieve P sustainability is to reevaluate our cultural relationship with human waste as something only fit for “flushing away.” In fact, human waste contains valuable P resources. (For me, reading The Humanure Handbook started my cultural reawakening.) Overcoming these cultural hurdles will be a necessary step in changing policies and regulations that guide how we manage wastes and P resources in the future to maintain agricultural productivity levels.

CLF Visiting Scholar Dennis Keeney adds the following notes. *The IFDC (International Fertilizer Development Center) estimates supplies sufficient for the next 300–400 years worldwide. **The world’s largest producer, exporter, and user of P is the United States. Data from the U.S. Geological Survey suggests that the U.S. has only 25 years of mineable P left, but this needs verification. *** Phosphorus (P) is associated with freshwater eutrophication, while nitrogen (N) is associated with hypoxia in estuaries, such as the Dead Zone in the Gulf of Mexico.




  1. I’m curious as to why P runoff is associated with freshwater eutrophication, while N runoff is associated with dead zones in estuaries. Why the distinction?

  2. Dennis Keeney

    Posted by Dennis Keeney

    Brent, this is a question of minimum nutrient needs. There is enough P in most ocean estuaries that N is limiting algal growth. Conversely, there is enough N in most fresh water systems that P is limiting. In fresh water systems, algae that fix N are stimulated by P, and nasty blooms happen. In the ocean, it is primary productivity that settles to the estuary floor and uses oxygen, causing hypoxia. So it is a combination of issues.

    Let me know if you have more questions.

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