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Is a Soil Thermometer a No-tiller’s Go-to Tool?

Soil covered with old crop residue, or cover crop residue, can make a huge difference in the amount of soil microbial activity taking place on your farm.

A simple soil thermometer – less than $10 at your local farm supply store – should be one tool you use during field scouting this summer, says Chuck Markley, resource soil scientist for the Central Platte NRCS district in North Platte, Nebraska.

The builders of organic matter are earthworms, microbes and insects, all of which can be easily found in soils that are cool and moist, Markley told producers at the No-till on the Plains Whirlwind Expo near Paxton, Nebraska June 3.

“Just like humans, these soil workers have basic needs: food, water and shelter,” he reasons. “Look at an irrigated field. You may not find earthworms, there, because water is just one-third of the equation.

“If food and shelter [from heat] are not provided, the workers will leave,” says Markley, who scouted fields in Perkins and Keith counties in western Nebraska on May 28.  While air temperature was 85 to 90 degrees F, he found vast differences in soil surface temperature in conventional, strip-till and no-till fields.

The results showed a 30-degree temperature difference between soils covered with one-inch of residue, to bare soil:

  • Conventional tilled fields, soil temperature at the surface ranged from 95 to 117 degrees F.

  • Strip till fields, soil temperature at the surface ranged from 110 to 117 degrees F.

  • No-till fields, soil temperatures at the surface ranged from 79 to 112 degrees F.

  • Gaps in residue cover also increase soil temperature. Small gaps increased soil temperature 3 to 20 degrees; large gaps, 20 to 30 degrees.

At each location, Markley measured earthworm activity 6-inches beneath the soil surface. Where soil temperatures were greater than 100 degrees, there was none. Where the soil was 92 degrees and lower, there was 1 earthworm (at 92 degrees) to 4 earthworms (at 79 degrees).

“Earthworm activity peaks when soil temperatures are between 50 and 90 degrees,” Markley says. “Above 95 degrees, and they die.”

Earthworms are just one component of healthy soils. They tunnel throughout the soil profile, moving nutrients and depositing castings, both of which help boost soil microbial activity. When soils are too hot – like can happen during the summer heat throughout the High Plains – microbial activity slows, or may even be eliminated.

Paul Jasa, Extension engineer at the University of Nebraska, likens the environment of hot soils to that of the pasteurization process for milk. “We use high heat to get rid of bugs in milk. All those beneficial microbes in soil will be killed when soil is unprotected by crop residue,” he explains.

Markley encourages farmers to take soil temperature observations during scouting trips this summer, and measure the amount of earthworm activity in these fields.

“University of Nebraska-Lincoln climatologists estimate that droughts will be longer more severe and more common over the next 80 years,” he says. “Keeping soil covered and cooler will be even more important from now on.”

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