Ensia

New study finds recycled phosphorus could fertilize 100 percent of U.S. corn

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Courtesy of Ensia

The world has a problem. A phosphorus problem.

Needed to fertilize crops, the bulk of phosphorus comes from nonrenewable phosphate rock. While China mines the most — producing almost half the world’s phosphorus — Morocco alone controls three-fourths of global phosphate rock reserves. Year by year those global reserves dwindle, leaving phosphate rock that’s ever lower in quality and ever harder to extract. At the same time, as agriculture expands over the coming decades, experts project increasing demand for mineral phosphorus.

Pair declining supply and rising demand with the lopsided geographic distribution of phosphate, and it’s not hard to see why experts think prices are likely to go up, which could threaten global food security.

At the same time, excess phosphorus, including that running off feedlots and released from wastewater treatment plants, threatens water quality and ecosystem health as it fertilizes lakes, rivers and ocean waters around the globe.

A recent study in Science of the Total Environment examined one solution to these twin problems: recycling. Looking at what recycled phosphorus could do for corn in the United States, the country’s number one crop, the study’s authors found that we’d need just 37 percent of available recyclable domestic phosphorus to fertilize all of the corn in the country.

The researchers did the math for animal manure, human waste and wasted food — all of which contain phosphorus that traces back to farmers’ fertilizer — and found that these three sources could furnish more than 1.9 billion kilograms (4.2 billion pounds) of phosphorus each year, with almost 90 percent from manure alone. That’s more than enough to sate American corn’s 724 million kilogram (1.6 billion pound) annual appetite for the element.

Spatial analysis showed that we could meet three-fourths of demand with phosphorus recycled in the county of origin. Additional phosphorus would have to travel an average of 302 kilometers (188 miles) to reach farms that need it, meaning that most corn-producing states could fill demand within their borders. Currently only 5 percent of U.S. cropland sees any manure fertilizer at all.

While the study’s conclusions are surprising, the authors caution that they don’t intend to propose public policy. Instead, their paper is meant as a “proof of concept” looking at the potential of recycling phosphorus for U.S. corn. Regulatory, logistic and economic concerns remain topics for future work to tackle.

For example, the fact that 25 percent of phosphorus for corn would have to come from counties outside that in which the corn is grown underlines the spatial disconnect between phosphorus sources and phosphorus demand in the U.S. According to the researchers, that reality — stemming from the separation of farm animals and crops — has intensified since the 1970s. Potential fixes, the researchers suggest, might involve innovative technologies for better phosphorus recycling, which would let farmers get more phosphorus from other sources nearby, making it less necessary to look beyond county border. A more direct, though perhaps more ambitious, solution might be sociopolitical efforts to bring livestock and cropland closer together again.

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