CORVALLIS - Once a month for the last three years, members of John Selker's research group have been driving the back roads of Lane County checking approximately 160 groundwater monitoring units.
Impetus for the ongoing study came from farmers in the county wanting to know if their activities affected the aquifers that supply much of the county's water.
There hadn't been any complaints, but the growers and Oregon State University Extension agent Ross Penhallegon wanted to take a proactive approach before water quality became a public concern.
There is reason to be cautious, said Selker, a bioresource engineering professor who conducts research through OSU's Agricultural Experiment Station.
Many residents of Lane County get their drinking water from groundwater, he explained. Similar areas in the United States with intensive agricultural production have experienced some problems. Shallow wells common to parts of Lane County are particularly sensitive to contamination, he added.
The 160 sample collectors, called "lysimeters," are buried three feet below the ground. They border 20 farms that represent a cross-section of the county's agriculture, Selker explained.
"We're testing for pesticide and nitrogen fertilizer leaching from orchards, berries, mint, grass seed and several row crops," he said. "These high-value crops are often implicated in groundwater contamination. Because they are high yield, it's cost-effective for farmers to add extra inputs such as pesticides and fertilizer. The good news is there were no pesticides found by any of the sample collectors."
But there was good and bad news about nitrogen fertilizer. Nitrogen leaching into the groundwater was a problem on some farms, but it wasn't tied to any particular type of crop.
"This demonstrates that any of the local products can be grown without adverse effects on the aquifers," said Selker. "We believe that the problems we did see can be controlled through better management.
"Although we can make suggestions, this is not a case of the researchers telling the growers what to do," he added. "This is a good example of teamwork. Everyone is on the same side. Better management is an outgrowth of an ongoing dialogue amongst the 20 farmers in the study. They are sharing ideas and crop yield figures with each other.
"We have at least one-and-a-half years more in this study and we will be looking more closely at nutrient management, irrigation and cover crops," he said. "Cover crops show excellent promise for reducing nitrogen leaching while having a host of other desirable features."
When cover crops such as ryegrass are planted after harvest in the fall, the roots bind the nitrogen that might have leached into the groundwater during the winter rainy season, Selker explained. The grass is plowed under before planting the main crop in the spring to add nitrogen and organic matter to the soil.
"We have a Mediterranean climate in the Willamette Valley," said Selker. "Most of the annual rainfall comes in the winter. This is also the time of the year when there is the least amount of sun to aid evaporation."
The result is nitrogen left in the soil in the fall that can leach into the groundwater over the rainy winter.
"There are, of course, other things that can cause groundwater contamination - septic tanks, golf courses, residential fertilizer use - but this is an agricultural study," Selker noted. "This is also a great model of how growers, researchers and the community can work together."