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Why the 2019 Harvest Has Set the Stage for Future Compaction

Subsoiling is an option to deal with compaction, but make sure it will be beneficial.

The sopping wet harvest conditions of 2019 in the Upper Midwest will leave a scar for 2020 and beyond in the form of soil compaction, says Dick Wolkowski, a University of Wisconsin soil scientist who spoke at this week’s Conservation Tillage Conference in St. Cloud, Minnesota.

“2019 was a bugger,” he says. Many farmers in the Upper Midwest faced an agonizing choice – get the crop out or have it stand all winter and risk yield loss from maladies like ear droppage and wildlife depredation. Harvesting on wet soils, though, has set the stage for future compaction.

Subsoiling is a method some may use to alleviate compacted areas in fields next year. It’s expensive, says Wolkowski. “You need a large tractor, and you will also use a lot of fuel.”

Farmers who subsoil should aim at running knives an inch or two below the compacted layer, says Wolkowski. That’s why it’s important for farmers to assess where the compacted layer lies. Farmers may not have their own penetrometer, but they may work with a crop consultant who does and who can use this tool to check compacted layers.  

“Also, leave some check strips just to see whatever it cost you was worth it,” he says.

Granted, staying off wet fields is one of the best ways to prevent compaction. In falls like 2018 and 2019, though, that wasn’t always possible due to limited harvesting time windows. Jodi DeJong-Hughes, a University of Minnesota Extension educator, points out that an effective strategy of reducing compaction potential is maintaining proper tire inflation rates and decreasing axle loads. 

Radial tires can be inflated to as low as 6 to 8 psi, but producers should check with their tire dealers to confirm proper tire pressures. Frequently checking and maintaining proper pressures will not only help reduce soil compaction, but will also improve tractor efficiency, she says.

Wolkowski adds controlled traffic patterns that sacrifice some field portions for traffic paths help prevent equipment from compacting broader field areas. If the above practices to minimize compaction are not followed, compaction will again occur, he says.

“It’s like taking a Sudafed for a sniffly nose,” Wolkowski says. “You’re treating a symptom, but you are not going to cure the problem.”

Cover Crops and Herbicide Carryover

Practices like cover crops can help alleviate compaction, says Jennifer Hahn, executive director of the Minnesota Soil Health Coalition. They have other perks, too, including:

  • Increased organic matter over time. 
  • Better competition that help suppress weeds. 
  • Nitrogen fixing.
  • Increased water infiltration.

Still, cover crops aren’t all blue sky and eatin’ peanuts. Cover crop performance can be hindered by herbicide carryover. Herbicide carryover can be impacted by several factors, such as application rates and organic matter content, says Dan Smith, University of Wisconsin (U of W) southwest regional specialist in the nutrient and pest management program.

It’s here where winter rye has a big advantage because it has had no negative effects from herbicide carryover in U of W tests, says Smith. Meanwhile, herbicide carryover impacted such cover crops as rapeseed, radishes, turnips, and annual ryegrass in U of W trials.

Still, weather can make or break herbicide carryover. A 2013 analysis of several cover crops found myriad herbicide carryover across several cover crops. In 2014, though, no herbicide carryover injury to cover crops occurred. 

The difference? “We had phenomenally better weather (in 2014) between herbicide application and by the time we planted cover crops,” he says. “We received a lot of rain in the interim.”

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