Saturday, October 15, 2011

Facing up to Phosphorus

Facing up to Phosphorus

Photo Courtesy of Ostara Nutrient Recovery Technologies Inc.; Phosphorus pellets made from wastewater
We can’t live without this essential element—yet at the same time we’re having an increasingly hard time living with it. What in the world are we going to do?
In Aldous Huxley’s dystopian Brave New World, citizens contribute to society even after death. As gases exit a crematorium smokestack, a special device recovers phosphorus—“more than a kilo and a half per adult corpse.” The recovered phosphorus then fertilizes all manner of plant life, which thrives on this vital nutrient recycled from the remains of the dead.
Huxley’s account is remarkable because it was written in the early 1930s, when far less public attention was devoted to the supply of natural resources. In fact, the full potential of phosphorus would be demonstrated several decades later. Its targeted use fueled the green revolution of the 1960s and 1970s, which dramatically improved crop yields and helped minimize the proportion of the world’s population remaining underfed.
Farmers around the world have come to depend on manufactured inorganic fertilizers containing key plant nutrients phosphorus, nitrogen and potassium to enhance soil fertility, especially in the otherwise poor soils of most tropical settings. But while all three are relatively abundant in nature, commercially viable sources of phosphorus to make these fertilizers could be exhausted just a few decades from now. That prospect, which remains a source of heated debate, has spurred a drive to recover the significant quantities of this element that disappear in the waste streams of cities and farms. Such recovery would have a bonus benefit: Even without the threat of shortages, minimizing the disposal of phosphorus is increasingly key to preventing degradation of valuable freshwater resources.

Momentous Shift

The availability of nitrogen, phosphorus and potassium in soil is a limiting factor in plant growth. The limitation imposed by phosphorus is the strictest, based on the amount of this material that plants take up and concentrate. Since all living organisms incorporate phosphorus in varying chemical combinations, modest amounts are relatively easy to obtain from biological sources. Spreading animal manure on fields is among the oldest known ways to add phosphorus to a crop. Urine can also be effective. Guano from birds and bats is exceptionally rich in this regard, as is bone meal.
Yet even as Huxley was writing, and certainly by the time the green revolution rolled around, such organic inputs were no longer sufficient to match the scale of agricultural output. As a result, most of the phosphorus that ends up on fields today comes not from organic materials, but from inorganic phosphates extracted from geological deposits.
This distinction makes no difference to crops. For our society and economy, on the other hand, the shift has been nothing less than momentous.
“Today, we are effectively dependent on phosphorus from mined phosphate rock,” says environmental scientist Dana Cordell, a research principal at the Institute for Sustainable Futures in Sydney, Australia. In many places, such as Brazil or central Africa, phosphate-based fertilizers are essential to maintaining crop yields and ensuring domestic food security. And that, Cordell says, spells trouble. For her, inorganic phosphates represent a nonrenewable resource that contrasts sharply with traditional sources of phosphorus such as manure, which are integrated into a natural environmental cycle. And because they’re only found in certain areas, global politics comes into play.
“Increasing environmental, economic, geopolitical and social concerns about the short- and long-term use of phosphate rock in agriculture means there is a need to reassess the way crops obtain their phosphorus and humanity is fed,” she says.

Peak Phosphorus?

Some, including Cordell, see a limited future for the conventional mining of phosphates. Easily obtained, high-quality deposits of this material will become harder to find, and its price could be expected to rise accordingly. Production should ultimately peak as commercially viable supplies become more limited, reducing the amount of phosphorus available for use as fertilizer. This reduction would be reflected by declining agricultural production in some parts of the world, along with the specter of mounting hunger.

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