Healthy soil and sustainable growing

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The dark side of nitrogen
Stephanie Ogburn 4 Feb 2010 3:00 PM
http://www.grist.org/article/2009-11-11-the-dark-side-of-nitrogen

Few people spare a thought for nitrogen.  But with every bite we take—of an 
apple, a chicken leg, a leaf of spinach—we are consuming nitrogen. Plants, 
including food crops, can’t thrive without a ready supply of available 
nitrogen in the soil.

The amount of food a farmer could grow was once limited by his or her ability 
to supplement soil nitrogen, either by planting cover crops, applying manure, 
or moving on to a new, more fertile field. Then, about 100 years ago, a 
technical innovation enabled us to produce a cheap synthetic form of 
nitrogen, and voila! Agriculture’s nitrogen limitation problem was solved.  
The age of industrial nitrogen fertilizers had begun.

The breakthrough, by German chemists Fritz Haber and Carl Bosch (rhymes with 
posh), made it possible to grow many, many, many more crops per acre. For the 
last 50 years, farmers around the world have used synthetic nitrogen 
fertilizers to boost their crop yields and drive the 20th century’s rapid 
agricultural intensification.

But in their fervor to increase yields, farmers often dose their crops with 
more nitrogen than the plants can absorb. The excess is now causing serious 
air and water pollution and threatening human health. Ironically, all that 
fertilizer may even be ruining the very soil it was meant to enrich.

Nitrogen, it seems, has a dark side, and it has created serious problems that 
we are only now beginning to reckon with.

Nitrogen kills a bay

To see nitrogen’s ill effects up close head to the mid-Atlantic coast and 
visit the Chesapeake Bay, the nation’s largest estuary. Once the site of a 
highly productive fishery and renowned for its oysters, crabs, and clams, 
today the bay is most famous for its ecological ruin.

On Dec. 9, 2008, the Environmental Protection Agency’s restoration program 
for the Chesapeake Bay marked its 25th anniversary. Other than the passing of 
the years, there wasn’t much to celebrate. The Chesapeake Bay Program’s goal 
is rehabilitation of the vastly polluted estuary, yet its 2008 “Bay 
Barometer” assessment found that “despite small successes in certain parts of 
the ecosystem and specific geographic areas, the overall health of the 
Chesapeake Bay did not improve in 2008.” (The fight to save the Chesapeake 
continues; in 2009, President Obama ordered the federal EPA to lead the 
ongoing cleanup efforts, but groups involved are still arguing over the 
details.)

A significant portion of the Chesapeake Bay pollution comes from agricultural 
operations whose nutrient-rich runoff—in the form of excess nitrogen and 
phosphorus—fills the Bay’s waters, leading to algal blooms, fish kills, 
habitat degradation, and bacteria proliferations that endanger human health.

The nitrogen runoff comes from the synthetic fertilizer applied to farm 
fields, as well as the manure generated from the intensive chicken farming on 
the east bay. Of course, the nitrogen in that chicken manure—some 650 million 
pounds per year, according to The New York Times— can largely be traced to 
synthetic nitrogen; the chickens are merely recycling the synthetic 
fertilizer that was originally applied to feed crops.

This type of reactive nutrient pollution is now so common that the dead 
zones, acidified lakes, and major habitat degradation it can cause are 
occurring with greater frequency, not just in the Chesapeake Bay, but in 
other parts of the United States and around the world.

Bombs away: Synthetic nitrogen comes of age

Nitrogen is ubiquitous. It makes up 78 percent of the earth’s atmosphere. But 
atmospheric nitrogen is inert. It exists in a stable, gaseous form (N2), 
which plants cannot use. Unless nitrogen is made available to plants, either 
by nitrogen-fixing bacteria in the soil or by the application of fertilizer, 
crops won’t grow as productively.

The German chemists Haber and Bosch found a way around this availability 
problem. Originally conceived as a way to make explosives for war, their 
technique turned inert nitrogen gas into highly reactive ammonia (NH3), a 
form of nitrogen that can be applied to soil and absorbed by plants. With 
their discovery, nitrogen ceased to be a limiting factor in agriculture.

The widespread use of synthetic fertilizer took off after World War II when 
innovations allowed nitrogen fertilizer to be produced inexpensively and on a 
grand scale. When Norman Borlaug, a leader of the Green Revolution, and other 
plant breeders began developing and exporting dwarf, high-yielding, 
fertilizer-loving varieties of corn and wheat, the new chemical fertilizer 
addiction went global. In 1960, farmers in developed and developing countries 
applied about 10 million metric tons of nitrogen fertilizer to their fields. 
In 2005, they applied 100 million metric tons.

This order of magnitude increase coincided with the Green Revolution. Indeed, 
nitrogen fertilizer is largely responsible for the phenomenal crop yield 
increases of the past 45 years. Without the additional food production fueled 
by nitrogen fertilizer, researchers estimate that two billion fewer people 
would be alive today.

Shifting shapes, getting around

Modern agriculture—and, consequently, present-day human society—depends on 
the widespread availability of cheap nitrogen fertilizer, the ingredient that 
makes our high-yielding food system possible. But the industrialization of 
this synthetic nitrogen fertilizer has come with costs.

The high temperatures and very high pressures needed to transform N2 to NH3 
are energy intensive. About one percent of the world’s annual energy 
consumption is used to produce ammonia, most of which becomes nitrogen 
fertilizer. That’s about 80 million metric tons (or roughly one percent) of 
annual global CO2 emissions—a significant carbon footprint.

Nearly half that fertilizer is used to grow feed for livestock. Herds then 
return the nitrogen to the landscape, where it contributes to several 
different kinds of pollution—the second cost of synthetic nitrogen.

Synthetic fertilizer is made with reactive nitrogen—that’s what makes the 
fertilizer easy for plants to use. As it turns out, though, reactive nitrogen 
doesn’t always stay where you put it. Farmers may apply this synthetic 
fertilizer to their cornfields, but the nitrogen in it will happily engage 
with the soil carbon, oxygen, and water in its environment. This is the 
essential problem with reactive nitrogen—its ability to morph and move 
around, often to unhealthy ends (see illustration).

Nitrogen infographic.

Estimates vary on just how much nitrogen escapes from fields and remains 
reactive and potentially harmful, but it’s not unreasonable to assume that 
plants absorb 30 to 50 percent of the nitrogen in the soil. So if a farmer 
applies 125 pounds of nitrogen fertilizer to an acre of corn, 30-50 percent 
of it will end up in the corn; as much as 70 percent—or 87 pounds per 
acre—could end up somewhere else.

‘N’ stands for ‘Needs to improve’

There is an obvious way around this nitrogen problem: use less fertilizer 
more efficiently. But there’s not much incentive to cut back.

Farmers get paid by the ton, which makes yields the driving force of modern 
agriculture. Most agronomists agree that farmers can get the same yields 
without applying as much fertilizer and manure as they now do. But few 
farmers are willing to take that chance. Many farmers use fertilizer as a 
form of insurance; better to apply a little too much and get high yields than 
apply too little and risk yield (and profit) declines.

 The challenge then is to find a way to provide plants with enough nutrients 
to maintain high yields while also minimizing nitrogen leakages. This may 
sound straightforward, but it’s tough to find mainstream farmers who are 
using nitrogen efficiently and safely. There simply aren’t incentives to do 
so. Fertilizer is cheap, and polluters don’t pay.

The situation might change if nitrous oxide becomes regulated under climate 
legislation. But in the climate bills currently making their way through 
Congress, agricultural emissions are explicitly exempted from any cap. Even 
if ag-related nitrous oxide emissions did get capped, policies would have to 
address efficiency directly. Otherwise, a climate-focused policy risks 
encouraging farmers to adopt practices that simply force the reactive 
nitrogen in another direction—into ground and surface water, for example.

Farmers don’t over-apply nitrogen on purpose. Nor do they want to contribute 
to estuary pollution and dead zones. But for 40 years, we’ve invested in a 
type of agriculture that rewards high yields over all other considerations.

U.S. grain farmers operate under pressure to generate volume, and have little 
or no incentive to conserve synthetic nitrogen along the way. Under the Farm 
Bill, commodity farmers get subsidies based on how many bushels they churn 
out, not how efficiently they use nitrogen. Even when fertilizer prices 
spiked in 2008, synthetic nitrogen remained a remarkably cheap resource—and 
corn farmers had every economic reason to lay it on liberally.

In their 2009 paper in the Annual Review of Environment and Resources, 
researchers G. Philip Robertson from the University of Michigan and Peter M. 
Vitousek from Stanford noted that the cost of applying a little additional 
nitrogen to a cornfield is more than paid for by the marginal gains in yield. 
In other words, corn is really cheap—but nitrogen is even cheaper.

Scientists now know that this arrangement can’t last forever—agricultural 
intensification has come with enormous costs. They also know there are other 
ways to manage crops and reward farmers. The Rodale Institute’s research on 
high yield production using cover crops to build soil organic matter and 
biologically fix nitrogen provides one example of a potential alternative to 
current practices. But the incentive structure around farming must change.

No longer can farm-support policy blindly push maximum yield. Farmers should 
be rewarded at least as much for conserving nitrogen and building the organic 
matter in soil. Rodale’s research suggests that those goals can be achieved 
without sacrificing much in the way of long-term yield.

Twenty-five years ago, the Commonwealths of Pennsylvania and Virginia, the 
state of Maryland, and the District of Columbia formally agreed to cooperate 
with the United States Environmental Protection Agency, in order “to fully 
address the extent, complexity, and sources of pollutants entering the 
[Chesapeake] Bay.” As it turns out, the Bay and other nitrogen-threatened 
ecosystems need more than cooperation to get healthy. They need the kind of 
political will that will take nitrogen efficiency and impacts seriously—and 
force actual changes to agricultural practices. And endangered ecosystems 
need for those changes to happen soon. We don’t have another quarter century 
to spare.