By Denise Lana,
Spurred by information presented at the Lanesboro, Minn., water forum, this is the second in a series of three articles exploring the issue, with further detail from each of the presenters, and an introduction to the principles of what impacts the watersheds of the region. Further articles in the series will run in the Driftless Journal over the next few weeks. The full water forum was recently uploaded to YouTube (search “Fillmore County Water Quality Forum 2023”) and is available to the public.
A hundred years ago, Minnesota and Iowa farms averaged 150-170 acres and were home to diversified crops and livestock. Through the years, new technology like tractors, combines and milking machines replaced animal power and helped families farm more land. Hybrid seeds, vaccines and commercial fertilizers were developed. The 1950s saw the introduction of chemicals to control weeds, pests, insects and diseases. Crop yields continued to increase, and many farmers began focusing on single crops that would produce higher yields and greater financial gains. In 2021, the average size of a farm in Iowa and Minnesota ranged from 359-377 acres, with corn and soybeans topping out as the two states’ main crops.
Besides being consumed as food for humans, corn has numerous uses. Many plastics are corn-based and corn starch is used in the making of matchsticks and pellets used in pellet stoves. Corn is a primary ingredient in feed for livestock and as a source for ethanol, corn contributes 10 percent of the fuel used by cars in the United States.
Soybeans are used for human food, and soybean meal is part of animal feed for poultry and livestock. Soybean oil is found in paints, plastics and cleaners, and is often used a biodiesel fuel with lower pollution emissions than petroleum diesel.
Minnesota’s top export crops are soybeans and corn, with soybeans accounting for 26 percent of the state’s agriculture export in 2022. Also in 2022, Iowa was the top US state in the exportation of corn (except seed corn) and soybeans, producing 14 percent of the nation’s soybean crop.
Corn and soybean crops need high amounts of nutrients to flourish, usually in the forms of commercial fertilizer or manure. Because nitrogen is the most yield limiting nutrient for corn and soybeans, a high nitrogen fertilizer like urea is often applied to the crops to produce maximum harvest. Also, even though manure contains low concentrations of nitrates, whenever it is used as a fertilizer and spread on a crop, the ammonium in manure mixes with nitrate already in the crop’s soil and converts to nitrates.
Enter Martin Larsen, a fifth-generation farmer and member of Olmstead County’s Soil and Water Conservation District. He is also a self-proclaimed soil health strategist, focused on reducing nitrates and increasing conservation and stewardship among farmers.
According to Larsen, farmland use is directly related to nitrate concentration in Minnesota springs and streams. A 2009 study, performed by Justin Watkins of the Minnesota Pollution Control Agency, consisted of Watkins evaluating the impact of row crops by sampling water from caves located beneath the crops. These samples, known as cave drips, are when surface water seeps down through the porous ground and drips onto stalagmites that are part of the underground karst caves. His research discovered that farmland use is directly related to nitrate concentration in cave drip samples. As a cave enthusiast, Larson was excited by the study.
Larsen took Watkin’s information and applied it as he evaluated several different crops and collected cave drip samples beneath each crop for comparison. The first crop in Larsen’s study was grassland planted as part of the Conservation Reserve Program, where the land is not farmed or ranched, but used for conservation benefits. Larsen then evaluated a rotation corn and soybean field with no manure applied. Larsen discovered the cave drip sample collected beneath the grassland had a near zero nitrate concentration, whereas the sample from beneath the corn and soybean field had a nitrate content of 16.6 parts per million.
“These drips are most compelling, because when you are 60, 70, 125, 198 feet in the ground collecting water from the ceiling, and you know where you are on the landscape, and you look at that land’s data, it’s compelling,” Larsen expressed. “It was an ‘aha!’ moment for me.”
Larsen implemented this information when he began studying Olmstead County’s Bear Spring Shed in 2018. He documented and mapped all 1,750 acres of land in the spring shed, and repeatedly collected water samples from five different sources and plotted his findings. Corn and soybean crops accounted for more than 80 percent of the land usage. While tabling solutions to lower nitrate levels. Larson discovered when 200 acres of corn were removed and replanted with alfalfa, a nitrate neutral crop, and cover crops were planted on 100 percent of the rest of the acres, the expected nitrate levels for the spring shed dropped from 27 ppm to 10.1 ppm, just below the government mandated 10.4 ppm bench line for nitrates.
“Logistically this would be difficult, but we’ve got to figure out how to get cover crops and row crops to 12 inches,” stressed Larsen. “The SWCD introduced a cover crop program, working with the landowners, and we are about 25% of the way there, the trend line (for nitrate levels) is pointing down. It’s important to share that there is optimism out there.”
Larsen, who hadn’t implemented any soil health practices on his own farm prior to 2016, began adopting them. In 2020, started growing significant row crops with covers along with his corn and soybean crops, and in 2021, he grew an oat crop followed by a legume crop. Nitrate concentrations went from 12 ppm down to 5 ppm at the spring on his property. Nitrates in his private well, which measured 10.8 ppm in early 2020, dropped to 3.8 ppm by the end of 2021.
“It’s pretty compelling that we can move the needle by growing cover crops that reach at least 12 inches high, that we get this 30-60 percent reduction in nitrates below row crops, we get it out of corn and soybeans and into something else, and we have an increase in hay and grazing acres,” Larsen explained. He added that 69 farmers have signed up with the cover crop program through the Olmstead’s Soil Health Program, and 10 farmers are enrolled in the alternative crops program.
“The end result is we, indirectly through all these farmers and all the cover crops they are growing, saved 23 semi-trailer loads of urea, a nitrogen source, out of the groundwater in Olmstead County,” Larsen beamed.
Presenter at the recent Lanesboro, Minn., water forum.
Minnesota farmer and soil health strategist, Martin Larsen, discovered in a study that on a farm with 1,750 acres comprised of 80 percent corn and soybean crops, if 200 acres of corn was removed and replanted with alfalfa, the expected nitrate levels in runoff water dropped from 27 ppm to 10.1 ppm, just below the government-established limit for nitrates.
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