Two scientists from the USDA’s National Soil Tilth Laboratory found lingering effects of a study that was finished nearly 30 years ago.

Mark Tomer and Michael Burkart, associate professors at the Soil Tilth Lab, had planned to research one issue, but found a high level of nitrates in a watershed instead.

They were planning to conduct research on groundwater and crop rotations at two watersheds at the Agricultural Resource Service Deep Loess Research Station near Treynor in southwest Iowa.

In the previous study by ARS, researches had applied different amounts of nitrates to fields within the two watersheds and then tracked the results for a number of years.

When Tomer and Burkart monitored the nitrate level in the first watershed at a 60-foot depth, they found an unusually high level of nitrates. By comparing the concentration level with stream flow levels, they were able to connect their findings to the old experiment.

The danger in finding the high levels of nitrates only five to six feet above groundwater makes the water harmful to drink, Tomer said.

“Agriculture has been linked to nutrients in ground and surface waters,” Tomer said. “Better nutrient management, crop rotation and other practices can reduce this movement and the quality of surface runoff water may improve rapidly. But improvement in groundwater and in stream flow that is fed by groundwater is difficult to predict and depends on many factors.”

New crop rotations were established in 1996 to help reduce the movement of nitrates.

“We expect the six-year rotation to show less nitrate leaching, but we won’t be able to prove that using stream monitoring until we have a few more years of data collection and analysis,” Tomer said.

Tomer said ARS has been working with watersheds since the mid-1960s.

A watershed is an area where all the rain which falls on the surface exits at one point.

“The land within a watershed is like a bathtub,” said Jerry Hatfield, lab director at the Soil Tilth Lab. “The rain that falls within the bathtub all runs toward one point — the drain.”

By looking at the results of the study 30 years later, scientists now wonder how long it will take past practices to fade.

Right now, no one knows how long these effects of the nitrates could linger underground, Tomer said.

Hatfield said ARS has an advantage because of its long-term database. They often go back and use the information from these past datasets, he said.

“This is something that short-term studies can’t see,” Hatfield said.