Nitrogen Fertilizer: Agricultural Breakthrough–And Environmental Bane

By Sarah Simpson
March 20, 2009; Scientific American

A new report citing drawbacks of the corn ethanol craze casts a pall over the centennial of a Nobel Prize-winning discovery that transformed global food production

100 years of green: Has the discovery of nitrogen fertilizer been fruitful in the long run?
One hundred years ago this month, a laboratory experiment at the University of Karlsruhe in Germany set the stage for the Green Revolution. Chemist Fritz Haber placed a sheet of osmium in a steel chamber, pumped in a mix of nitrogen and hydrogen gases, and cranked up the heat and pressure. Then, out flowed ammonia, the elusive raw material for producing synthetic fertilizer. It was the eureka moment scientists had been pursuing for a decade: Haber managed to create the necessary conditions to transform nitrogen gas, abundant in the atmosphere but useless for life, into a digestible form. The work would earn Haber the 1918 Nobel Prize in Chemistry. (Many protested the award because Haber had been instrumental in developing and deploying chlorine gas for Germany during World War I.)

Once implemented on an industrial scale, ammonia synthesis enabled the widespread fertilization of croplands for decades hence. As a direct result, the world’s population skyrocketed from 1.6 billion to six billion during the 20th century. But Haber’s nourishing discovery has a dark side he probably never imagined. The boom of fertilizer, long injudiciously applied, has come at a high price for the environment.

And now, according to a new report to be released later this month by the Scientific Committee on Problems of the Environment (SCOPE) of the International Council for Science, society’s aspiration to use biofuels to kick its oil addiction could backfire. By intensifying nitrogen pollution, a business-as-usual approach to biofuels production could exacerbate global warming, food security threats and human respiratory ailments in addition to familiar ecological problems. Scientists have long known that the reactive nitrogen in fertilizers leaching from agricultural fields (as well as those smaller amounts exiting tailpipes and smokestacks) wreak havoc as they cascade through the air and rivers. Rogue nutrients often spur harmful algal blooms as they flow into the ocean, and hundreds of estuaries around the world suffer from so-called seasonal dead zones as a result. "We’re getting to the point where dead zones will be continuous bands around the continents," warns marine ecologist Jeremy Jackson of Scripps Institution of Oceanography in La Jolla, Calif.

Fixing the nitrogen problem is at the heart of Jackson’s call to make the Green Revolution truly green, a sentiment echoed by scientists around the world. A primary culprit: so-called first-generation fuels, which are based largely on fermentation of cane and corn sugars.

"The production of ethanol from corn in the U.S. is a disaster in terms of fertilizer flowing down the Mississippi River," says Cornell University environmental biologist Robert Howarth, chair of the International SCOPE Biofuels Project. The U.S. Energy Independence and Security Act of 2007, passed with strong bipartisan support, set a goal of producing 54 billion liters (14.3 billion gallons) of ethanol from corn by 2022. But new research outlined in the SCOPE report indicates that, without a change of practice, meeting that goal could increase the nitrogen flux in the Mississippi by 37 percent. That pits ethanol production overwhelmingly against another national goal: reducing nitrogen flux in the same river by at least 40 percent to reduce the size of the dead zone in northern Gulf of Mexico.

Corn is a troublesome biofuel source, particularly from a nitrogen standpoint, Howarth says. Typical corn-growing practice is to apply high doses of fertilizer, with substantial losses to the surrounding environment. Corn has very shallow roots compared to most crops and so can use nitrogen only in the top one to two inches (0.4 to 0.8 centimeters) of the soil. Moreover, it only takes up nitrogen and other nutrients for 60 days out of the year. Other crops such as soybean and wheat have deeper roots that are active longer. But the rising price of corn has encouraged farmers to grow more of this "nitrogen leaky" grain. Land set aside for conservation purposes as well as some active soybean and wheat fields are being converted back to active corn cultivation.

Still, this growth in corn production cannot hope to enable the world to reach its ethanol production goals, the report says. The U.S., for example, put 24 percent of its 2007 corn harvest into ethanol, yet that generous contribution amounted to only 1.3 percent of the nation’s use of liquid fuels. Based on this and other early findings, the SCOPE report projects that substituting 10 percent of the liquid fossil fuels used for transportation with biofuels could require a third of the world’s arable land, causing trouble not only with nitrogen pollution but also food security.
But that vision is still several years off, Howarth points out. Meanwhile, the SCOPE report suggests that even grassoline may not be the best use of biomass: "The world would be better off using the cellulose directly for combustion," Howarth says. "If you try to use biomass in a stationary way, it’s much more efficient." Direct combustion of switchgrass for heat and electricity can provide 2.6-fold more energy than converting the same source to ethanol—and 9-fold more energy than producing ethanol from corn. The proof is out there: 35 percent of homes and commercial buildings in Sweden are heated by combustion of biomass, mostly willows grown on nearby plantations.

Biofuels are a hot topic right now, but the litany of issues surrounding fertilizers and nitrogen pollution are far more complex. Foremost among the challenges is the need to use more fertilizer to combat hunger in many parts of the world, points out ecologist Alan Townsend of the University of Colorado at Boulder. Townsend, like Howarth, has spent much of the past 15 years analyzing the human perturbations to the global nitrogen cycle. More fertilizer is badly needed to help feed burgeoning populations in much of the developing world, and yet mistakes of the West are being repeated elsewhere. A study published in February suggests that China could cut its fertilizer use by a third without reducing crop yield. Pursuit of meat-intensive diets, which requires massive production of fertilized crops to feed animals, is another problem Townsend and Howarth point out.

Despite their dire warnings, neither scientist is a pessimist. Haber’s discovery has been a miracle for a century, Howarth says. We just need to be smarter about how we apply it.