Editors’ Note: Did you ever wonder why On Pasture’s Rachel Gilker knows so much about soil? Well, in addition to all her academic training, she is also assisting Dr. Ray Weil, as he writes the latest edition of THE textbook on soils. “The Nature and Properties of Soils” is basically the be all and end all when it comes to books on this topic. On Pasture is honored that Dr. Weil is sharing this excerpt with our readers. It’s also an opportunity for us to all begin thinking of a solution to this important problem.
Many scientists argue that improving the efficiency of phosphorus use in farming is not only essential for profitable agriculture, but is a moral obligation to future generations that will have to depend on Earth’s limited phosphorus supplies. The immediacy of this concern is not shared by everyone, but the importance of conserving phosphorus is based on two facts that are quite indisputable: 1) phosphorus has no substitute and 2) it is not a renewable resource.
All living things require phosphorus as it is literally in their DNA. Humans need phosphorus in their own diets. Soils need phosphorus if they are to support the plants and animals we use for food. There is no substitute for phosphorus in these roles. Economists tell us that generally goods will be replaced by something else if scarcity drives up prices. For example, if copper becomes too expensive, fiber optic cables might replace copper wires; or if fossil fuels become too expensive, people may invest in wind power to replace oil and gas in generating electricity. Since phosphorus is a basic chemical element in the structure of many essential cellular components (DNA, RNA, membranes, ATP), no such substitution will be possible.
Phosphorus is a non-renewable resource—and one that is in quite limited supply, both in absolute global amounts and in geographic distribution. The vast majority of the world’s mineable phosphorus is in the North African country of Morocco. Historical examples and current resource theory suggest that as the best, easiest to mine deposits get used up first, the remaining resources get harder and more expensive to mine and refine. Thus accelerating resource exploitation to meet growing demand will eventually be limited first by escalating costs and then by dwindling absolute supply, resulting in a maximum or peak rate of production when just over half of the total resource has been used up (Figure 14.32). The remaining deposits will continue to be mined for decades beyond that time, but in ever smaller amounts and at ever greater expense. While there is considerable disagreement about the actual size of world phosphate reserves and how long they will last (estimates range between 100 and 400 years to exhaustion), the data suggest peak production will come much sooner than once thought – perhaps by the middle of this century. Hence there is growing sense of urgency among many scientists and policy makers (see for example the European effort).a
On the positive side, same phosphorus atoms can be used over and over again – if they are not so carelessly dispersed as to make them virtually unrecoverable. The current model is unsustainable. We mine phosphorus (P) and apply it as soluble fertilizer only to have much of it wash off P-saturated farmland into streams and then into the oceans. Even most of the phosphorus that crops do take up and use makes its way indirectly to the oceans after a one-way trip through the food to sewage system. For these reasons – not to even mention the damage P causes in eutrophication of aquatic systems – there is a growing belief that the time has come for individuals and societies to learn more efficient and sustainable methods of using our infinitely precious but definitely finite phosphorus resource.
a For reviews of the complex issues and varying estimates involved with Peak Phosphorus concept, see Cordell and White (2011) Peak phosphorus: Clarifying the key issues of a vigorous debate about long-term phosphorus security. Sustainability 3:2027-2049 and Scholz et al. (2013) Sustainable use of phosphorus: A finite resource. Science of The Total Environment 461–462:799-803. . For perspectives on the “trilemma” involving geopolitics, poverty and resource limitations, see Obersteiner et al (2013) The phosphorus trilemma. Nature Geoscience 6 897-898. and Wyant et al (2013) Phosphorus, food, and our future Oxford University Press,, Oxford, UK. 224 p.