Soil and Fertilizer

The Downside of Fertilizers

In a belated celebration of Earth Day, this fourth in our April series on soil focuses on the negative side effects of various soil amendments and on hopeful signs we can do better. We are all familiar with the phenomenon of eutrophication, algal blooms that overwhelm waterways when too much phosphorous runs off from agricultural operations. Nitrogen fertilizers also can easily volatilize, leading to emissions of nitrous oxide, which has hundreds of times the warming potential of CO2. However, as the second article below details, the exploitation of these resources has led to human rights violations as well as environmental degradation. The example of the Rich Earth Institute offers hope that we may be able feed a growing population without destroying the planet in the process.

Reducing nitrogen use key to human and planetary health: study

The use of chemical fertilisers helped fuel the four-fold expansion of the human population over the last century.

Better management of nitrogen-rich fertilizers through alternating crops, optimizing use and other measures can yield huge environmental and health benefits, but must boost food production at the same time. Reducing nitrogen pollution from global croplands is a “grand challenge,” the group of international researchers said in a study published in Nature outlining a dozen urgently-needed reforms.

The intensive use of chemical fertilizers helped fuel the four-fold expansion of the human population over the last century, and will be crucial for feeding 10 billion people by 2050. But the bumper crops of what was once called the Green Revolution have come at a terrible cost. Today, more than half the nitrogen in fertilizers seeps into the air and water, leading to deadly pollution, soil acidification, climate change, ozone depletion and biodiversity loss.

Earth’s natural “nitrogen cycle” has been massively imbalanced by the use of some 120 million tons of chemical fertilizer each year. Less than half of that input is actually absorbed by plants, with the rest seeping into the environment and causing a constellation of problems. Researchers led by Baojing Gu, a professor at Zhejiang University, analyzed over 1,500 field observations from croplands around the world and identified 11 key measures to decrease nitrogen losses while still enhancing crop yields. One such method is crop rotation where a variety of crops are planted on the same plot of land, optimizing the flow of nutrients in the soil. The benefits of slashing agricultural nitrogen pollution are some 25 times higher than the implementation costs of about $34 billion, they found.

Phosphorus Saved Our Way of Life—and Now may End It

Bou Craa conveyor belt from the phospahe mine. Photo from flickr, taken on 11 March 2013 in Western Sahara near Laayoune Marsa Boujdour. Photo by jbdodane.

Like nitrogen, phosphorous soil amendments were an important part of the Green Revolution that enabled us to feed so many more humans. And like nitrogen amendments, using phosphorous as a soil amendment comes with unanticipated costs. Writing in The New Yorker, Pulitzer Prize winning author Elizabeth Kolbert details the sordid colonial history of guano exploitation in Peru and South Pacific Islands. Once the accumulated bird poop of thousands of generations had been consumed by farmers in Europe and the US, and the nesting sites of many birds destroyed, science stepped in to invent chemical ways to extract nitrogen from the atmosphere and phosphorous from rock. As Kolbert writes: ” The longest conveyor belt on earth begins in the town of Bou Craa and runs for sixty miles across Western Sahara to the port city of El Marsa…. The conveyor carries phosphorus-rich rock, which is mined in Bou Craa and then shipped from the coast to places like India and New Zealand to be processed into fertilizer. The mine, and indeed the vast majority of the rest of Western Sahara, is controlled—illegally, by most accounts—by Morocco, which possesses something like 70% of the planet’s known phosphorus reserves.”

The political fragility of Western Sahara is just one worrying aspect of the future of phosphorous use. Phosphorus is critical not just to crop yields but also to basic biology. DNA is held together by what’s often called a “phosphate backbone”; without this backbone, the double helix would be a hash. Isaac Asimov described phosphorus as “life’s bottleneck.” What distinguishes it from other elements that are essential to life—carbon, say, or nitrogen—is its relative scarcity. The atmosphere contains almost no phosphorus. Phosphate-rich rocks, meanwhile, exist only in limited quantities, in certain geological formations. China holds the world’s second-largest reserves—these are less than one-tenth the size of Morocco’s—and Algeria the third-largest.

There are parallels between the exploitation of guano in the 19th Century and phosphorous in the 20th Century. The Bou Craa mine is the main reason Morocco illegally invaded Western Sahara in 1975. The descendants of tens of thousands of refugees from Western Sahara are still living in refugee camps in Algeria today. Meanwhile, phosphorous use in agriculture has led to increasing large “dead zones” in waterways and oceans around the world. Harmful algal blooms caused by phosphorous leaching into waterways can also contaminate water supplies and cause illness. Scientists warn that, as nutrient loads continue to grow and the planet heats up, the problem will only get worse.

The Rich Earth Institute in Brattleboro, Vermont, works for “a world with clean water and fertile soil achieved by reclaiming the nutrients from our bodies”.  The Institute encourages donations of urine from the local community. Arthur Davis, who directs Rich Earth’s Urine Nutrient Reclamation Program, explains, “Around 60% of the phosphorus we excrete comes out in our pee.” Peecycling can cut down on the amount of conventional fertilizer that the farmers purchase. (Urine contains not only phosphorus but also large amounts of nitrogen and potassium.) At the same time, it keeps nutrients out of the sewage system and, by extension, it is hoped, out of Vermont’s waterways. It may also help to avoid some of the human and environmental rights violations associated with the historical exploitation of phosphorous.

Credit: Unsplash/CC0 Public Domain

(See also: Phosphorus shortage could affect worldwide crop yields)

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