Peninsula Pride Field Day focuses on soil depth data

“Every farm field in Kewaunee County is unique,” Nathen Nysse, a consultant with Tilth Agronomy, told a group of about 50 farmers, agricultural industry reps and residents recently.

Nysse was one of the speakers at a Field Day event sponsored by Peninsula Pride Farms held April 22 at El-Na Farms in the town of Lincoln to help educate farmers and others about watershed issues in the county.

Helping farmers to determine the depth to bedrock on individual farm fields and gain a better understanding of karst topography are key to addressing runoff issues in Kewaunee and Southern Door counties, said Don Niles, a spokesperson for Peninsula Pride Farms.

In the Karst region, which includes many areas in Kewaunee County, farmers can improve mapping of bedrock depths on their fields so that manure and other fertilizers can be spread to better avoid ground and surface water contamination, Niles said.

Many farmers are experimenting with different agricultural practices to better control soil erosion and runoff in sensitive karst areas, according to Niles.   These include being aware of sinkholes and other land features of karst topography that provide direct conduits to groundwater.

The term karst is defined as a geologic formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite, producing fissures, sinkholes, underground streams and caverns, according to an article provided by University of Wisconsin Discovery Farms.

Karst limits the soil’s capacity to filter contaminants from percolating water.   And when karst features like sinkholes form in areas of concentrated flow like waterways or closed depresssions, large volumes of surface water can directly enter groundwater with little or no filtration, the article said. .

Dennis Frame, from the University of Wisconsin-Extension told the audience that obtaining accurate soil data is essential to addressing groundwater issues.

In Wisconsin, soil surveys began in the early 1900s and gradually updated so that today all of the soil in the state has been mapped, Frame said..  However, the age of the most recent soil surveys can vary significantly by county, he said.

In Northeast Wisconsin, glacial geologists have done extensive mapping, but the information is often not detailed enough for field-specific use by farmers, according to Frame.

There are several tools to measure depth to bedrock on individual fields, Frame said.  One method used for measuring soil depth to bedrock is a bucket auger, which is helpful, but the auger may refuse to dig further because of large rocks imbedded in the soil or glacial till.  This can result in errors with the depth of bedrock underestimated, Frame said.

The University of Wisconsin-Extension’s Discovery Farms program in 2008 purchased a seismometer on a skid,  known as a Geoprobe,  to assist farmers with their nutrient management planning. Because it is on a skid, it can be moved easily across farm fields and, by using shockwaves that are sent through the soil by a pulse, produces more accurate readings of soil materials and depths.  However, this technology can be slow and may pick up interference that can result in an inaccurate reading.

Another way to measure soil depth is with a Veris, which uses GPS and other computerized technology to measure depth to bedrock, Nysse said.  The reports generated will measure to a depth of 3 feet.   It provides a method to measure larger fields and identify spots that may require further examination for karst features, Niles added.

Using county well construction reports is another way to determine depth to bedrock and Kewaunee County is currently doing this as part of their groundwater studies, said Eric Cooley of the UW-Extension.

He explained that the new sonar technology is much more complicated for use on a field than on a lake, where depth readings are easy to take.

He said that he recently took measurements on one field that was “like a washboard” with ripples than went up and down every few feet when taking depth to bedrock measurements..

“Depth of soil information is important for anyone putting things on land or living on it,” said Frame.

This article originally appeared on Green Bay Press Gazette: Peninsula Pride Field Day focuses on soil depth data