Could This Slimy Corn 'Fix' One of Earth's Biggest Pollution Problems?
The slimy substance found in the Sierra Mixe corn indigenous to Mexico allows the corn to fix its own nitrogen by providing shelter for the microbes which convert the type of nitrogen in the air into more usable forms.
Credit: Mars, Incorporated

It probably doesn't look like any corn you've seen. At 16 feet (5 meters), it stands about twice as tall as conventional corn. And sticking out of the stalks, high above the ground, are aerial roots, red finger-like protrusions coated in slime.

But despite this alien-like goo, this species of corn — indigenous to the Sierra Mixe region of Oaxaca, Mexico, where the locals have long been cultivating and eating it — is remarkable for another reason. It's the only corn that scientists know of that can take in nitrogen directly from the air and use it to grow.

Nitrogen is an essential nutrient, and the ability for a major crop to use atmospheric nitrogen would change the world, reducing the nitrogen pollution that's become one of the biggest environmental problems afflicting the globe. [The Reality of Climate Change: 10 Myths Busted]

All living organisms need nitrogen. It's needed to build the proteins, for example, that allow organisms to function and grow. But although the atmosphere is 78 percent nitrogen, it's out of reach from animals and most plants. That's because the nitrogen in our air consists of two nitrogen atoms, tightly bonded together, and that requires a lot of energy to break,  said Alan Bennett, a plant biologist at the University of California, Davis, who helped analyze the nitrogen-fixing corn.

Among crops, only legumes, such as soybeans, beans, and alfalfa, can access this nitrogen — and only with the aid of bacteria. The microbes use an enzyme to convert —or "fix" — atmospheric nitrogen into usable form, compounds such as ammonia (a nitrogen molecule bonded to three hydrogen molecules) or nitrate (a nitrogen bonded to three oxygen molecules), Bennett said.

Most major crops, such as corn, wheat, and rice, can't, according to R. Ford Denison, a crop ecologist at the University of Minnesota.

Because crops can't convert the nitrogen in the air to a form they can use, farmers must provide fixed nitrogen for them in the form of fertilizer. In the early 20th century, the German scientist Fritz Haber developed what's known as the Haber-Bosch process to convert atmospheric nitrogen into ammonia — the basis of synthetic fertilizer that now feeds nearly half the world. "Without the ability to produce synthetic fertilizer, we wouldn't be able to produce enough food for the current population," Bennett said.

The problem is that it's hard for farmers to estimate exactly how much fertilizer is needed, leading to overuse and waste. About 57 percent of the nitrogen in fertilizer ends up polluting the environment, said Xin Zhang, an environmental scientist at the University of Maryland Center for Environmental Science.

This influx upsets the natural nitrogen cycle of Earth. Normally, nitrogen gets recycled back into the soil. The nitrogen in plants, for example, is in a usable form, so when they drop leaves, seeds or simply die, the nitrogen returns to the soil for other plants to use. Animals also bring usable nitrogen back to the soil through urine and feces. "The key thing is that nobody was taking any nitrogen far away," Denison told Live Science.

When crops are shipped across the world, nitrogen does not get recycled — forcing farmers to replenish it with fertilizer.

In a 2009 analysis in the journal Nature of the world's major environmental problems, researchers found that nitrogen pollution has already passed the point where it can lead to devastating consequences. The only two other problems where the planet had exceeded such a threshold were climate change and the loss of biodiversity, according to the analysis.

In the U.S., for example, excess nitrogen from fertilizers ends up in rivers and waterways, draining into the Gulf of Mexico. Algae gorge on the nitrogen, proliferating as algal blooms. But when the algae die, the bacteria that cause decomposition guzzle all the oxygen in the water, creating so-called dead zones that kill sea life. The National Oceanic and Atmospheric Association estimated the dead zone in the Gulf of Mexico to span an area about the size of New Jersey.

Nitrates can also seep into the water supply at toxic levels. Some nitrogen can be released into the air as nitrous oxide (two nitrogen molecules bonded to an oxygen molecule), which depletes the ozone layer and is a greenhouse gas that causes global warming, Zhang said.

The production of fertilizer itself is also an energy-intensive process that produces greenhouse gases. Fertilizer is expensive, and wasting it can cost billions of dollars worldwide, according to David Zilberman, an agricultural economist at the University of California, Berkeley.

With the U.N. forecasting that the population will near 10 billion by 2050, the demand for food — and nitrogen — will only intensify.

The slime on the Sierra Mixe giant Mexican corn, which scientists described in a new study published in PLOS Biology on Aug. 7, feeds a community of bacteria that fixes nitrogen in the air. Although this mucus-covered maize has some scientists excited, it probably won't solve anything right away. "This corn is of course very productive for the community it's grown in, but it's not directly applicable to conventional production systems of corn," Bennett said. For one, it takes eight months to mature — much longer than conventional corn's three months.

The researchers measured that the corn fixed from 29 percent to 82 percent of its own nitrogen. But that amount is negligible compared to what farmers require for their fields, Denison said.

Still, studying it might help researchers engineer or breed nitrogen-fixing corn — either by itself or with the help of bacteria — that can feed the world. The challenges are, nevertheless, immense, Denison said.

To fix nitrogen, bacteria need a lot of energy, which requires oxygen. But oxygen breaks down the enzyme that the microbes rely on for fixing nitrogen. Legumes solve the problem by housing the bacteria inside nodules in the roots, where the plant can control how much oxygen the microbes receive. To engineer or develop this capability in corn is a huge challenge. "I don't see any prospect for that happening in my lifetime," Denison said.

Bennett is much more sanguine. Biotech companies, agriculture corporations, startups and even the Gates Foundation have poured resources into developing nitrogen-fixing crops. "I'm pretty confident that all these approaches will converge in some ways within five or 10 years," he said. "We're likely to see a significant level of nitrogen fixation occurring in conventional maize crops."

If such technology does come to pass, and it works for other crops as well, the benefits would be huge. Poorer farmers who can't afford fertilizer, such as those in southern Africa, would be able to boost their yields to the tune of $2.5 billion to $7.2 billion, Zilberman said. In the most optimistic case, he said, full adoption could lead to $17 billion to $70 billion in cost savings worldwide.

"This technology will be revolutionary," he said. "It will be good for farmers, it will be good for consumers, and it will be good for the environment."

In the meantime, farmers can adopt strategies to deliver fertilizer only when and where it's really necessary. As part of what's called precision agriculture, new technology like sensors and drones are helping farmers be more efficient, Zhang said.

Originally published on Live Science.