Vertical Tillage is Not No-Till
Iowa conservationists with USDA's Natural Resources Conservation Service (NRCS) are disturbed by the number of row crop farmers using vertical tillage tools. Vertical tillage often leaves the soil covered with crop residue, but it is not the same as true no-till.
Vertical tillage equipment is used to lightly till the soil and cut up residue, mixing and anchoring a portion of the residue into the upper few inches of soil while still leaving large quantities of residue on the soil surface.
Several NRCS soil conservationists say they've spoken with farmers who practice vertical tillage on D slopes (9 to 14 percent), and they refer to it as no-till when it is a different practice altogether. "There is a lot of misinformation out there," said Curt Donohue, district conservationist with NRCS in Newton. "One pass with a tillage tool — even with high amounts of residue remaining — can dramatically increase soil loss."
Tillage Destroys Soil Structure
Barb Stewart, state agronomist for NRCS in Iowa, says that although vertical tillage leaves large amounts of crop residue cover, the tillage impacts are significant. "Soil disturbing activities, like tillage, destroy soil structure," she says. "When this happens, it limits a soil's ability to function properly and leaves topsoil susceptible to erosion on steeper slopes."
Kevin Kuhn, area resource conservationist for NRCS in Atlantic, says when soil is disturbed, the soil structure and habitat for soil organisms gets destroyed, water infiltration is reduced, runoff is increased, and soil quality declines. "Tillage disrupts the soil's natural biological cycles and wrecks the structure of the soil, making it susceptible to erosion," says Kuhn.
He says no-till is Iowa's most important conservation practice in the fight against soil erosion. "I don't want to knock vertical tillage because it's good at leaving residue cover," he said, "but the goal of no-till is to reduce surface disruption and therein lies the difference between the two practices."
No-till Critical On Steep Slopes
No-till is most important for erosion protection on steeper slopes. During heavy rains in April, Donohue says no-till fields had relatively minor erosion compared to tilled fields. "Even fields with high residue levels where vertical tillage tools were used had extreme sheet and rill erosion and relatively severe ephemeral erosion compared to no-till fields," he said.
Stewart says no-till alone is often not enough to eliminate erosion on steeper slopes, but that a combination of practices, such as no-till, contour farming, contour buffer strips, terraces, grassed waterways, and field borders, need to be established to truly slow down the erosion process. "During April's heavy rains we saw several instances of sheet and rill erosion on steeper slopes where there was no tillage," she said. Stewart also mentioned cover crops as a practice that can help protect against erosion during the winter and early spring.
Stay In Compliance
Since 1985, conservation compliance has been a requirement of all USDA program participants. Any tillage not accounted for in your conservation plan may put a farmer out of compliance with erosion provisions. Don Carrington, NRCS resource conservationist in Des Moines, says if a producer makes a full-width tillage pass through a field when no-till is required, that producer may no longer be compliant with the highly erodible land provisions of the Farm Bill. Carrington recommends farmers check with their local NRCS office before:
Using any new tillage equipment.
Conducting any tillage if your conservation plan calls for no-till.
Fixing small gullies on highly erodible land from ephemeral erosion.
No-till — Now You Know
There is a misconception that if you leave a field covered with residue, you are a no-till farmer. No-till is not just about leaving residue on the soil surface. It is also about stopping the disturbance of the soil structure. Any tillage, regardless of its depth, will undo all of the benefits of any previous no-till farming if it fractures the consolidated soil and breaks the macro-pores. This includes losing any improvements in soil quality gained by previous investments in no-till.
No-till is not:
Using a rotary harrow (Phoenix or Phillips harrow)
Using a row crop cultivator
Using a vertical tillage tool
Incorporating manure with disk covers
Tilling ground every other year or once every four years
Kevin Kuhn, Area Resource Conservationist, USDA-NRCS, Atlantic, Iowa