When Dan Mehlhaf heard weather forecasters warn in early May last year that a strong storm was on its way, he and his family took precautions. Both he and his wife went home early from work to their Hutchinson County, South Dakota home on May 12. Around 4:00 p.m. they watched out their window in disbelief as daylight turned to darkness in a matter of seconds.
“When I say darkness,” Dan recalls, “this wasn't just kinda dark, this was pitch black where you could not see your hand in front of your face. I had never experienced anything like that. It reminded me a lot of some of the pictures and some of the accounts I had heard about the Dust Bowl days of the 1930’s, and it was quite scary.”
The darkness lasted a few minutes. The intense straight-line winds of the derecho storm that followed lasted only 15 minutes, but the damage they caused was immense. Corn seedlings were sandblasted and shorn. Soybean plants were cut down by the wind. Trees and buildings sustained major damage. Some vehicles were thrown into road ditches, car windows were blown out, and car panels dented with interiors filled with gravel and corn stalks. A wife of a friend was blown around so violently while she was shutting the doors on a machine shed that she broke an ankle and sustained torn ligaments.
Dan farms with his son in Hutchinson County, about 30 minutes from Yankton, where he works as the District Conservationist for the U.S. Department of Agriculture’s Natural Resources Conservation Service. He recently spoke with Buz Kloot in a Growing Resilience podcast about the derecho, and the significant soil losses that occurred from two storms only a few weeks before.
High-damage winds a month earlier
The spring of 2022 had already set out distinctly windy and warm. But on April 14, 40-50 mile-an-hour winds blowing through the fields shocked Dan and his neighbors. That day, Dan noticed a relative of his online noting particularly bad wind erosion on a field about 30 miles northeast of Yankton. Dan drove to the field to meet his relative and was again shocked– the wind and flying dirt were so intense in the thick of the storm that he couldn’t even get out of his truck.
“Our pickups were side-by-side in the road,” he explains. “We rolled the windows down to talk, but we could only carry on a very short conversation because the dirt was blowing into the vehicle so bad, getting in our eyes. I took videos that day but I couldn't get out of the truck to do it.”
A few days later, Dan returned to the field. It had been tilled and then cut for silage, with no cover crop. The loose, dry Egan-Ethan soil, a silty-clay loam, had been totally displaced.
Dan noticed so much soil material had been blown into the road ditches that the ditches were level with the road in some places. He dug into this displaced material and found that it was all sand– a loamy sand that behaved like the sand in an hourglass. It would collapse easily in on itself. He pushed a yardstick down and discovered that it was 29 inches deep.
“There is a very small portion of sand in a silty clay loam,” Dan says. “It’s not very much. So what this tells you is that the smaller silt and clay particles that make up the predominant portion of this silty clay loam had gone airborne and just disappeared, blown who knows how many miles down the road. The only particle left was sand, which had bounced along the surface and ended up in the road ditch.”
Dan took a sample of the soil in to be tested, and found surprisingly high levels of nitrogen, phosphorus, potassium, and sulfur. Based upon the value of fertilizer, Dan did the calculations– that is $996 worth of nutrients in the road ditch.
Another storm hit on April 23rd, 2022, with 50-60 mile-an-hour winds. Dan and his son had been out in the field and they had to seek shelter in a shed, as they were physically being blown around. They could see soil from their neighbors’ land flying through the air.
15-ton soil loss in 15 minutes
The derecho on May 12 was modeled by USDA/NRCS National Erosion Specialist Chris Coriel, who found that 15 tons per acre of soil had been lost in those 15 minutes of straight winds. That 15 tons of soil lost from an acre would fill a dump truck––but what was more significant to Coriel was even more soil was lost on yet a third day of strong winds on May 7, just 5 days prior to the derecho. Coriel’s modeling showed that the 12 hours of sustained 20-25 mile-an-hour winds on that day– a more common occurrence in South Dakota, produced more soil erosion than the more exotic derecho.
Dan Mehlhaf was not surprised by the results of the modeling. He recalled distinctly hearing soil particles hit the car body and windows during the high winds on April 14 as he drove by unprotected land. Dan notes there was clearly a difference in soil loss from fields that had been clean-tilled compared to those with standing cover residue, or a cover crop.
For example– the Egan-Ethan silty clay loam that had blown so badly on April 14 was countered across the road to the south by a field with the same soil type. Both had been cut for silage, but this second field had been planted with a cereal rye cover crop after the silage was cut. The cereal rye was green and growing well, and that field did not blow. Dan explains that a well-planned cover crop is a primary factor in protecting soil from wind erosion, assisted also by no-till practices and good, intact residue.
Tillage trends change slowly
Though it is a slow process to change anybody’s mentality, Dan notes, he has observed through conservation tillage surveys a very slow trend in the direction of less tillage, and even towards no-till practices in some places.
The biggest change he’s seen is a skyrocketing of cover crop usage. “We really are seeing the adoption of less tillage and more use of cover crops in these dry years,” Dan explains. “There’s been just enough moisture to get the cover crops to grow and do what they’re supposed to do, thank goodness for that, because they’re really making a difference. This past winter, you really had to drive around and look to find a field that somebody tilled last fall. It’s not commonplace to till in the fall anymore.
“These past two years have really changed some mindsets on how much tillage we think we need to do,” Dan says. “And there’s less tillage being done, at least for the time being, and more cover crops. The rye is green and growing, and up about 2 inches right now (April 12, 2023) and looking beautiful.”
That would be gratifying news to former NRCS state conservationist Jeff Zimprich, whose vision was to “move the needle in soil health”– not just for producers but for people across the state. Dan is seeing that needle beginning to move. He’s seen a steady increase in adoption of conservation practices in the last two years. Even in 2019 when it was too wet to plant corn, he saw farmers planting a cover crop. “They saw the value of it in a wet year. Now they are seeing the value of the practice in a dry year,” Dan says. “Ideally this practice can become standard and habitual, and replace some of the conventional farming practices that had left soils thin and fields vulnerable to forces like the derecho.”
What is a derecho? https://www.weather.gov/lmk/derecho
SD NRCS’s derecho playlist shows some of the image and video material that Dan collected from April 14 to May 12, 2022
Kurt Lawton’s excellent article “Winds, tillage steal soil productivity in Dakotas” in the Dakota Farmer.
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