The Slow Dissolve

The Haber process, a means of converting nitrogen in the atmosphere into ammonia, has, among other things, allowed us to produce commercial fertilizer on a tremendous scale. Developed in the early 1900s, it was a game-changing invention that has been responsible for increases in food production worldwide. In 1900, the world’s population was 1.6 billion; today it’s more than 7 billion, and without the Haber process the rate of growth would undoubtedly have been much slower. (The process was also eerily incorporated into Judith Claire Mitchell’s novel A Reunion of Ghosts, which has very little to do with fertilizer but is nevertheless worth a read).

An article coming up in the May issue of Erosion Control will explore some of the benefits—and costs—of manufactured or synthetic fertilizers. Several programs exist, both through the US Department of Agriculture and through private organizations, to encourage farmers to apply less fertilizer so that less of it runs off and reaches surface waters, where it causes algae blooms and other problems. These voluntary conservation programs emphasize not only the water-quality benefits of reduced application, but also the cost savings of using no more fertilizer than strictly necessary.

But there’s a problem. As one of the people interviewed for our upcoming article, Eric Davidson of the University of Maryland Center for Environmental Sciences, points out, “There have been many experiments, including an insurance plan that guaranteed a price to farmers if they used less fertilizer, but it didn’t work. It turns out that putting on a little extra fertilizer is a pretty cheap insurance policy that is often a good investment. When the stars align to produce good weather and good commodity prices, a little extra fertilizer can result in a bumper crop. In years that the weather doesn’t cooperate as well, such as a drought, late frost, or other factors, they haven’t spent much on that extra fertilizer, so it isn’t a high risk for them. The bigger risk is letting the good years get away without reaping optimal rewards.”

Another person interviewed for the article, Rattan Lal, professor of soil science and director of the Carbon Management and Sequestration Center at The Ohio State University, notes, “We’ve been blaming agriculture for everything, but we forget that it’s feeding us three times a day.”

Research now underway in Sri Lanka might provide at least a partial solution to the problem of overfertilization. Fertilizer pellets containing urea—a combination of nitrogen, hydrogen, carbon, and oxygen—are cheap to manufacture and are commonly scattered on fields by farmers around the world. The pellets dissolve quickly during heavy storms, however, and much of the fertilizer is washed away without benefitting the crops. A team at the Sri Lanka Institute of Nanotechnology, led by Nilwala Kottegoda, has been adding hydroxyapatite—a component found in bone—to the urea. Hydroxyapatite is already used in extended-release drug tablets to make them dissolve more slowly, and the team hoped it would have the same effect here.

After promising results in the lab, Kottegoda enlisted farmers to test the pellets on rice paddies for several months; as described in this article, some test plots received no fertilizer, some received pure urea, and some received urea combined with hydroxyapatite that contained the same amount of nitrogen as the pure urea. As the article (from the UK-published Economist) says, “Plots that received no nitrogen-based fertilizer at all averaged 5.5 tonnes of rice per hectare. Those that received urea alone yielded 7.25 tonnes per hectare. Those fertilized with urea-hydroxyapatite managed 7.8 tonnes per hectare. Though the newly compounded fertilizer is more expensive to produce than its conventional equivalent, Dr. Kottegoda calculates that this cost would quickly be offset if using urea-hydroxyapatite obviated the need to re-scatter fertilizer over a paddy after heavy rain—and that does not even take into account the increase in yield it brings with a single application.”

No tests have been reported as yet on the amount of nitrogen in runoff from the various test plots, and tests have not yet been conducted to see whether use of the new fertilizer would allow farmers to use less phosphorus-based fertilizer as well.

Assuming the compounded fertilizer is produced on a large enough scale, do you think the increased crop yields—in the test case, about 7.6%—would be enough to encourage its use?