How much soil is disturbed by shallow vertical tillage? The answer depends on the tool, the soil and the tillage depth, says Kevan Klingberg, a University of Wisconsin Extension outreach specialist. Many farmers value these implements to size residue, condition the seedbed and incorporate nutrients, he says. But when it comes to using these tools on erodible cropland, the watchwords should be “conservative and shallow.”

In 2010, The University of Wisconsin’s Discovery Farms program evaluated the effects of spring shallow vertical tillage on soil disturbance and residue cover. Tools from Great Plains and Summers were tested on 14 fields at five farms.

The study concluded that, on average, a single pass on silt loam soil tilled about 40% of the field to a 2-in. depth. About 60% of the field was undisturbed. In addition, the study found that 80% of corn residue remained on the surface after one pass, and 80% of the previous year’s corn roots stayed in place. Intact roots “help minimize soil loss,” says Klingberg, who led the research.

However, soil disturbance and residue cover varied significantly, depending on soil type, tillage machine characteristics and operating depth, Klingberg says. Sandy soils, aggressive blades and deeper operation all moved more soil and left less residue cover.

In addition, the soil conservation benefits of one-pass shallow vertical tillage disappeared with two passes, which disturbed just as much soil as tandem disking, Klingberg says. Likewise, vertical tillage tools with concave blades mounted on angled tool bars dislodged more corn roots and exposed more soil.

Minnesota research from 2010 to 2012 also measured residue disturbance after shallow vertical tillage. A single spring pass with a Salford RTS or Summers Super Coulter vertical tillage tool left about 70% corn residue cover – comparable to strip-till, says Jodi DeJong-Hughes, University of Minnesota Extension tillage expert. Two passes with a Salford RTS left 21-30% soybean residue cover and 39-58% corn residue cover.