The World’s Farms Are Hooked on Phosphorus. It’s a Problem

Scientists have been pointing out the “broken” phosphorus cycle for more than a decade: Humanity has unearthed huge quantities of the element, which winds up in waterways instead of returning to cropland.

The problem comes down to crap. People and livestock eat crops and excrete phosphorus as a result. (A University of Iowa researcher calculated that the state’s livestock produce a load of excrement equivalent to a nation of 168 million people.) But most of it won’t end up feeding plants again. Waste treatment can loop sludge or manure back to being fertilizer, but transporting and treating it is often impractical, so it may sit in stockpiles and “dry stacks” without the chance to boost another crop.

Or the system may be leaky: Sewage, septic tanks, stockpiles, and eroded soil drip phosphorus into oceans and rivers, where it dilutes to oblivion while degrading those ecosystems. For instance, phosphorus runoff drives the harmful algal blooms that have killed Florida’s seagrass, starving thousands of manatees.

Demay’s model determined that in a 67-year span, humans…