Tracking Nitrogen Through the Soil to Reduce Pollution From Agriculture

Scientists are uncovering how nitrogen migrates underground with the help of sensors that continuously measure nitrate concentration and water flow.


On this gray, drizzly winter morning, the California coastal mountains in the distance look like a mirage hovering over a flat swath of fields at Russell Ranch, a 300-acre experimental farm in the Sacramento Valley. One of the researchers in charge is Martin Burger, an angular, intense-looking Swiss ecologist. He steps out of his Ford F-150 pickup and leads me down a gravely path to a field covered in neat rows of lime-green triticale — a cereal grain — and bean shoots.

Above ground, the scene looks orderly and static. But Burger and his colleagues at the University of California at Davis are interested in what lies hidden below the surface. Down there, it’s a highly dynamic and far-from-predictable scene. To get a glimpse, they have buried an array of instruments that can trace the trajectory of nitrogen. They are trying to help solve the many ecological and human health problems caused by this troublesome element while helping farmers grow crops more efficiently. 

Nitrogen has many faces. It is an essential element on the periodic table. No organism, plant or human, can survive without it. Yet there is a short supply of accessible nitrogen in the world. In fact, had scientists not created synthetic, mostly natural-gas-based fertilizer decades ago to improve nature’s method of “fixing” nitrogen — a process of breaking nitrogen molecules apart to make them available to plants — neither you nor I, nor most of the 7 billion people crowding the planet, would be here today. 

But here’s the rub: Chemical companies turn nitrogen found naturally in the atmosphere into ammonium and nitrate compounds that make up fertilizer. Soil microbes eventually transform the ammonium into more nitrate. This water-soluble form of nitrogen is a source of food for plants, but it makes a Jekyll-and-Hyde-like transformation when excess leaks into lakes and streams or groundwater.