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Is Nitrogen the New Carbon?

A discussion with ecologist Alan Townsend on mankind's love-hate relationship with nitrogen, and how this marriage can be saved.
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Nitrogen could be the new carbon.

Just as carbon is roughly seen in the popular imagination as the elemental culprit in climate change, nitrogen, which comprises four-fifths of the air that we breathe, may also become a prime-time villain.

But it's a complex villain at best. While the stable form of nitrogen in the air is no problem, "reactive nitrogen" — the chemically active form in things like ammonia and the air pollutant nitrogen oxide — can be. And nitrogen-based fertilizers are vital in producing enough food (and now fuel) for a planet with more than 6.6 billion mouths to feed. With the world's attention at least briefly focused on the food-cost crisis, fertilizer use will grow more necessary, not less.

A paper appearing in the May 16 edition of Science outlines the nitrogen conundrum and offers suggestions for reducing global nitrogen use by at least a quarter — enough, authors estimate, to offset expanding agricultural and energy uses. The paper's authors, led by James N. Galloway of the University of Virginia, are part of the International Nitrogen Initiative, a body that aims to maximize the benefits of nitrogen while minimizing its harms.

Defining the Problems

"Most of what we produce — for fertilizer and as a byproduct of industry — does not end up on our plates or in our gas tanks. Instead, reactive nitrogen cascades through air and fresh water, the ecosystems surrounding us, and the oceans on which we depend," wrote Alan R. Townsend, an ecologist and biochemist at the University of Colorado and one of the co-authors, in an e-mail to

A paragraph from a 2007 United Nations-sponsored report provides a depressing introduction: "In the air, (reactive nitrogen) can contribute to higher levels of ozone in the lower atmosphere, causing respiratory ailments and damaging vegetation. From the atmosphere, it generally falls to the surface in atmospheric deposition, generating a series of effects — corrosion of buildings, bridges and other human-made structures, acidification of soils and water bodies, and inadvertent fertilization of trees and grasslands, creating unnatural growth rates, nutrient imbalances and decreasing or altering biodiversity. Leaching out of the soils, reactive nitrogen can make groundwater and surface water unfit for human consumption. Reactive nitrogen also promotes eutrophication (algae buildup) in coastal ecosystems, which can negatively impact fish stocks and biodiversity. Eventually, most reactive nitrogen is denitrified back to molecular nitrogen, but a portion is converted to nitrous oxide, which contributes to both the greenhouse effect and to stratospheric ozone depletion."

And reactive nitrogen production is accelerating, having grown tenfold between 1860 and 1995, it increased another 20 percent — to about 412 billion pounds a year — in the decade that followed. While fossil fuels and industrial uses account for some of that, most of the explosion has come from dramatic expansion of agricultural cereals and meat.

There are parallels between the transformation of the world's nitrogen cycle and climate change, Townsend told But while "climate change represents a simple and broad-reaching message that can be boiled down to a couple of ideas, (the nitrogen cycle) represents an incredibly diverse array of benefits and problems that play out in different ways depending on where you are."

Inefficient use of nitrogen-based fertilizer in the United States, for example, leads to water and air pollution, while insufficient fertilizer in Malawi leads to starvation.

Unlike the effort to address climate change, Townsend said, rebalancing the nitrogen cycle doesn't automatically mean conflict — in part because a plethora of local solutions can be nearly as effective as a Kyoto-sized global one. "There are many solutions to this that are far less likely to require the level of global upheaval and cooperation needed. It's a problem that's easier to solve, since we can have less in the environment and still have what we need." Noting that the new president of the INI (replacing Galloway) is a soil scientist — Cheryl Palm with Columbia University's Earth Institute — Townsend makes pains to show that those beavering away on the issue aren't a bunch of scientific Cassandras. "For all the importance of the ‘too much' side," he said, "too much attention is being paid to that side of the problem." Where Yellow Means Go As Townsend explains to his students, "The ability to make nitrogen fertilizer is one of the greatest boons in human history." The Science paper cites estimates that 2 billion people would not be alive today except for the ability to artificially fix nitrogen from the air to use in fertilizer. It adds, ironically, that "in many developed nations, the products from N-intensive agricultural practices lead to unhealthy diets, whereas elsewhere a lack of synthetic fertilizers, combined with depleted soil nutrient reserves, directly contributes to widespread malnutrition."

Columbia economist and best-selling author Jeffrey Sachs, who heads The Earth Institute, discussed the developing world's nitrogen deficit earlier this week before a gathering of philanthropists in Santa Barbara, Calif. "This is the difference between famine and food surplus," he started, holding his thumb and index finger an inch apart. "It's putting basic inputs into agriculture."

He described standing in an African field with an institute scientist, who pointed to the flaccid and underperforming crops around them and told Sachs, "See that yellow there? That's nitrogen deficiency. What's needed here is a bag of fertilizer."

"Sub-Saharan Africa, it's all nitrogen deficient," Sachs summarized. "And each crop takes out a little bit that's left."

That's in the developing world, where subsidies and donations are keeping the so-called Green Revolution on life support.

In the first world, easy access to relatively cheap fertilizer can lead to both excessive use and a bias toward nitrogen-intensive products, Townsend said.

The ecologist, who lives in Boulder, Colo., said farmers in the Midwest will dump extra fertilizer on a field "almost as an insurance policy," the same way someone might pop a multivitamin in the morning in hopes of topping off their nutritional tank.

This comes after most likely having already over-fertilized, he said. In the most intensively fertilized crops, under normal application, half the fertilizer doesn't make it into the plant. But it does enter the runoff or the atmosphere as nitrogen oxide.

Our love affair with meat amplifies these issues, since it takes eight pounds of cereal to produce a pound of meat. And in an echo of climate change, as the people in the Third World gain wealth, they start to replicate the habits of the rich — like eating more meat. (In one of nitrogen's many ironies, Townsend noted that Mediterranean-style diets that feature less meat are healthier.)

"I don't think the solution to our problem is no meat consumption," Townsend said, adding, "I eat meat!

"But we have to change some of these trends."

Defining the Solutions

In this month's Science paper, the authors make four specific recommendations for reducing reactive nitrogen. They don't claim that their proposals, all based on current technology, are the answer, but they say their "interventions" would be enough to keep the world's nitrogen footprint from growing larger even as global agriculture, by necessity, expands.

In order of reduction, they call for controlling nitrogen oxide emissions from the burning of fossil fuels using "maximum feasible reductions," which could reduce reactive nitrogen emissions by 55 billion pounds of a year; increasing the efficiency of fertilizing crops (33 billion pounds a year); improved animal management policies (33 billion pounds); and ensuring that at least half the world's urban population has sewage treatment (11 billion pounds).

While stating that "other intervention points are clearly needed" and that implementing just these four proposals "would not be trivial, they indicate that a multipronged, integrated approach can decrease the amount of (reactive nitrogen) lost to the environment."

Townsend cited a program in the Midwest in which farmers are encouraged to use substantially less fertilizer on the fields, while leaving a single strip of planted land to be overdosed as usual. If that strip outproduces the field as a whole, the program rebates the difference. And if it doesn't, as has been happening, the farmer reaps the savings in fertilizer.

He also called for greater precision in application, which like energy efficiency technology, costs more up front but pays off in the stretch.

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