I cannot overemphasize the importance of phosphorus not only to agriculture and soil conservation but also to the physical health and economic security of the people of the Nation. Many of our soil types are deficient in phosphorus, thus causing low yields and poor quality of crops and pastures.
President Franklin D. Roosevelt, message to congress, 1938.

The basic building blocks of “life” are carbon, nitrogen, and phosphorous. Organic molecules which are the primary component of all living things have carbon backbones.  All proteins in, including DNA, are made of nitrogen-containing amino acids.  As I’ll explain in this week’s column, phosphorous is also a critical component in the process of being alive.  What distinguishes phosphorous from carbon and nitrogen is that we are in the process of running out of it.  As I will explain, this is a pretty big deal.
First let’s talk about why phosphorous is important. Some time back in high school biology you had a lecture on the Calvin Cycle, the process by which plants capture solar energy and store it by making glucose.  As I have covered in previous columns, the capture of solar energy by plants is the foundation for the entire food chain.   In order not to induce a wave of naps in my readership, I will not include a detailed review the Calvin Cycle here.  The key thing to know is that the process revolves around a series of phosphorous-containing molecules.   No phosphorous, no glucose, no food chain, no life.
The supplies of carbon and nitrogen in the biosphere are effectively limitless since both are recycled efficiently through natural processes.  The supply of nitrogen to plant life is also augmented by human activity through the conversion of atmospheric nitrogen to ammonia-based fertilizers using the Haber-Bosch process.  (See “Fun with Fritz and Carl” for more details.)  In contrast, there is essentially no recycling of phosphorous in the biosphere. 
While the initial commercial use for phosphorous was for matches, today the vast, vast majority of phosphorous is used to make fertilizers.  If plants don’t have phosphorous, they can’t execute the Calvin Cycle, so they can’t grow. Phosphorus is obtained by mining rocks which contain phosphates (phosphorous-containing compounds) and then dissolving the rocks in sulfuric acid to make phosphoric acid.  Once you have the phosphoric acid you can make a variety of fertilizers without difficulty.
The explosive growth in world population from 2.5 billion in 1950 to over 7 billion today was driven primarily by an equally impressive increase in the food supply known as the Green Revolution.  The Green Revolution was driven by dramatic increases in irrigation from massive dams on major rivers, as well as significant increases in the use of fertilizers all around the world.  As you can see from the graph above, not long after the warning by President Roosevelt to Congress shown above, phosphorous production in the world increased dramatically and the excess food supply allowed more people to reproduce and survive.
After the phosphorous-containing fertilizer is used it leaves the farm dispersed amongst the crops, livestock, eroded soil, and water run-off.  With the minor exception of bone meal from slaughter houses, this phosphorous cannot be recovered and reused.  The teacher and engineer in me really, really wants to go off on a long tangent on how this phenomenon demonstrates the concept of entropy in the universe and all of its amazing implications.  The part of me which is trying to become a better writer limited the discussion to the single sentence that follows.  After you use the phosphorous once, it’s dispersed into concentrations which are too low for it to be practical to recover it and use it again.
The graph at the top of the page tells another story as well, an important story. Like many other supplies critical to modern society such as petroleum and fresh water, global phosphorous production is leveling off and is about to begin declining.  There are two reasons which make limits of phosphorous particularly critical.

  1. There are absolutely, positively no substitutes for phosphorous.  Life evolved around the Calvin Cycle and the Calvin Cycle only works with phosphorous.
  2. We can’t make phosphorus.  Once we use up the phosphate rocks and disperse the phosphorous in low concentrations throughout the biosphere, that’s it.

Reduced phosphorous production will mean reduced food supplies for the world.  When people don’t have enough to eat bad things happen, like disease and war.  To keep things interesting, phosphate containing rocks are not evenly distributed throughout the world, with a staggering 90% of all deposits found in just five countries, Morocco, China, South Africa, Jordan, and the United States.  I’ll leave the reader to imagine the potential geopolitical implications of a shortage of phosphorus.
I realize that I have written yet another ominous and pessimistic column.  This was not my intent.  As odd as this may sound, I really just started this one because phosphorous is interesting (at least to me, but I am a pretty serious nerd). But over and over again, I keep stumbling across limits and tipping points in critical resources around the world.  This leads me back to what seems to have become the central theme to Common Science, that current and looming resource shortages are about to become the central driving force in human events and that those events are going to be, to put it lightly, tumultuous.
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