Flash in the Pan

Nitrogen fixation

| May 02, 2013

The massive fertilizer explosion in West, Texas, made less of an impression than the relatively small Boston blasts two days earlier. But if terrorists are scary, the dangers presented by stockpiles of ammonium nitrate, aka nitrate fertilizer, should be even scarier. This material can be used with bad intentions, such as the gasoline-soaked fertilizer used in the Oklahoma City bombings, and perhaps the pressure cookers of Boston. Or it blows up on its own, accidentally triggered by fire or some other disturbance. Ammonium nitrate is also an environmental contaminant, even when used for its intended purpose of feeding plants. If it is spread on the land in greater amounts than the crops can absorb, it's a problem.

Nitrogen fixation in a lab was first demonstrated in 1909. Under intense heat and pressure, atmospheric nitrogen was converted to ammonium nitrate, which was known to be good for plants as well as explosives. The Haber-Bosch process, as it became known, was developed with agriculture in mind. But when the U.S. entered World War II, it was put to work producing ammonium nitrate for blowing stuff up. When the war ended, factories that had been built to manufacture bombs switched to fertilizer. The sudden abundance of cheap nitrate fertilizer opened the door to modern factory farming.

There is much in modern agriculture to be wary of. There are plenty of scary pesticides, synthetic hormones and other sketchy additives. But while nitrate fertilizer is, in essence, a retooled war chemical, which is yucky, there are times when it appears to have much more upside than downside.

A paper published last April in Nature presented evidence that many organic farms are nitrogen-deficient, and suggested they would see improved yields with application of nitrogen fertilizer. The paper also found that conventional farms typically apply more nitrogen than their crops can absorb.

Organic sources of nitrogen include the growing and rotation of cover crops, the spraying of fish emulsion and other biologically based liquids and covering the ground with compost, manure or some other mulch. The process of getting these materials into place is usually labor-intensive, but worth it for reasons beyond the nitrogen, as it can improve soil structure, increase microbial diversity and help the soil retain moisture. The Nature paper notes that organic crops tend to have an advantage in drought situations.

Sometimes—quite often, according to the Nature data—organic practices don't supply as much nitrogen as crops can consume. If a farmer isn't in the position to truck in some solution, like composted llama manure, nitrate fertilizer might be the best option.

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Unfortunately, while using nitrates in moderation isn't a mortal sin, today's typical use is hardly moderate. With the stuff so cheap and abundant, farmers often spread considerably more than they need, and not as efficiently as they should. Every molecule of ammonium nitrate that isn't absorbed by the crop plant is a pollutant. Fertilizer runoff in rivers can lead to unrestrained growth of algae and weeds that can choke a river to death. Further downstream, in the ocean, nitrogen fertilizers can cause ecological dead zones.

As long as energy is cheap, nitrate fertilizer will be widely available. In its relatively brief period of existence thus far, fertilizer has fueled the growth of industrial agricultural commodities like corn and grains. I don't consider all of these advances to be desirable, but it's possible to be against corn syrup, ethanol, grain-fattened cattle and other products of modern agriculture, yet still accept an appropriate use of nitrate on farms that are doing their best but are still nitrogen deficient.

Agriculture is a complicated, contentious topic, and too often the debates are framed in binary terms like "organic" and "conventional," as if food were a two-party political system. Many studies have been done to see which one is better, with the results being applied to arguments on both sides of the divide. The Nature study was a meta-analysis of 66 studies comparing organic and conventional agriculture, and compared the respective yields of 344 crops. In this sample, conventional techniques outperformed organic methods in terms of overall yield, but differences varied greatly from crop to crop. It found organic crops to be generally nitrogen deficient and conventional crop systems generally oversaturated with nitrates.

The paper suggests hybrid farming could be useful in some contexts. Hybrid farming borrows heavily from organic practices but also is open to certain non-organic practices, such as targeted nitrate application.

One of the paper's authors, Dr. Navin Ramankutty of McGill University, told me by phone he's intrigued at the possibilities of hybrid farming, and thinks it could offer as-yet unquantified promise in subsistence situations, as well as more demonstrated potential for improving yield in commercial organic applications.

"I may not buy food if somebody was applying pesticides," Ramankutty said, "but I would certainly not mind if my farmer applied a little bit of chemical fertilizer on his farm. It's when we use 200 kilograms per hectare that the problem arises."

Two hundred kilograms is a little more than the 400-pound minimum amount of ammonium nitrate that the Department of Homeland Security requires must be reported for tracking and added security oversight. The plant in West, Texas, had an unreported 270 tons.

DHS didn't even know this stockpile existed until it blew up, which leads to to my next question: How many other undocumented storehouses of explosives are there? Our blasé attitude toward nitrogen is putting us in all sorts of danger. We need to take it more seriously, make less of it, and make the most of what we use. Otherwise we run the risk of having it blow up in our faces all over again.

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