This Is the Shit: Sewage Could Help Restore Depleted Farmland

Humans produce an average of 900 pounds of feces a year, which could be used to help reverse a global decline in the amount of arable land.
December 3, 2015, 6:06pm
Photo by Daniel Kiss/EPA

The world is losing farmland at a rapid rate to erosion and chemical depletion. Pollution and erosion have flushed away much of what makes our soil fertile, resulting in a loss of up to a third of the world's arable land in the past 40 years, British researchers reported this week.

But there might be a way to solve at least part of the problem that's right underfoot — in the sewers that carry away our wastes.

Going back to using what was once called "night soil" on crops is an idea that's being floated by a team led by Duncan Cameron, a professor of plant and soil biology at the University of Sheffield. Cameron said that European farmland has lost so much carbon that some observers fear the continent's productivity is nearing a tipping point.

"Across Europe, the yields of our major staple crops are stagnating. They're not increasing," Cameron said. "Since the 1930s, wheat yields, for example, increased year over year. Then in about 1997, it just stopped, and it hasn't really gone up since."

Using treated sewage on fields rather than high-nitrogen fertilizers would help restore carbon necessary for soil to absorb moisture and nutrients and keep alive the microbes that break down organic matter, he said.

"What we need to do is use a combination of biotechnology so we can make plants do what they used to do while keeping all of the things we want, like high yields and disease resistance," Cameron said. "It's kind of taking the best of modern technology and the best of practices from the 19th century and putting them together in a new, sustainable model for agriculture."

The average person produces about 900 pounds of feces a year.

Cameron and his colleagues presented evidence of what they called an "unfolding global disaster" Wednesday, on the sidelines of the global climate summit in Paris. But he said scientists should be able to produce crops within a decade that can be fertilized effectively with treated human wastes and put more carbon back into the soil.

"The technology is there, or thereabouts," he said. As long as we're comfortable with the notion that we're going to start using organic fertilizers a lot more frequently in conjunction with these new crops that we're breeding, we have a sustainable solution to the agricultural problem."

It's not like there's any shortage of those organic fertilizers: The average person produces about 1.5 tons of bodily waste a year, Cameron said, including nearly 900 pounds of feces.

Farmers commonly used feces — their own, or the manure from animals — to fertilize fields for centuries. But in the 19th century, the development of chemical fertilizers and pesticides since the 19th century made it easier for farmers to drop a concentrated load of nitrogen-rich plant food directly onto their fields, without the smelly mess or risk of illness, said Richard Mulvaney, a soil fertility expert at the University of Illinois.

But nitrogen fertilizers "are an unbalanced nutrient source" that doesn't support the microbes that break down organic materials in the soil, Mulvaney said. Meanwhile, the development of modern sewer systems separated organic wastes from the human environment, "so it's not readily available for soil application."

There have been health concerns raised about spreading sewage sludge, often dubbed "biosolids." Even when harmful bacteria are killed, environmental groups warn the material can sometimes contain heavy metals and other industrial wastes that seep into the sewers. The US Environmental Protection Agency has regulated biosolids since 1993, and says they're currently used on less than 1 percent of American farmland. A National Academy of Sciences review in 2002 found no sign that those rules had failed to protect public health, but recommended additional study.

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Organic wastes also contain high levels of phosphates, which are necessary for plants but can fuel algae blooms and oxygen-poor "dead zones" if they leach into waterways. It's a finite resource that ought to be conserved, Mulvaney said.

"It makes very good sense to recycle the excess nutrients back into the soil for more crop production," he said. "But they have to be managed in a way that doesn't promote pollution."

Cameron said that while his findings sound "a bit doom and gloom," he's optimistic that the problem can be fixed. But farmers "are in a very difficult position" and will need help converting to a more sustainable way of farming, which may mean higher prices in the supermarket, he said.

"We either pay for it now and secure the future food supply, or we pay for it later when food is running out and the markets cause food prices to spike," he said. "We're going to pay at some point, and we have to choose whether it's now or later down the line."

Follow Matt Smith on Twitter: @mattsmithatl

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