Now is a good time for strip-tillers to dig soil pits to assess root development, compaction and soil health, says Jodi DeJong-Hughes, University of Minnesota Extension strip-till expert.
"As farmers switch to strip-till from moldboard plowing and disc-ripping, it's good to compare the effects on soil aggregation and structure," DeJong-Hughes says.
Strip-till isn't a magic bullet — a sobering reality for impatient farmers who switch and expect everything will be fine in the first few years, she says. But over time, soil in strip-tilled fields responds positively when farmers quit using conventional tillage. That's what she saw in soil pits dug at a Morris, Minn., field day in early July.
Deep Roots Are Best
The pits were about 3½ feet deep in fields that had been strip-tilled, moldboard plowed and disc-ripped. The pits were dug across four rows of corn in fields that had been conventionally tilled for about 100 years before a 4-year tillage study started.
"I like to see full root development in August when I dig pits 3 to 4 feet deep," she says. "Digging the pits across four rows of corn will most likely reveal compaction from wheel traffic. Clean off the face of the soil pit with a shovel or knife."
But compaction may make it difficult to clean the surface with a knife, she admits.
"I bent the knife in the face of the soil pit dug in the moldboard-plowed field," DeJong-Hughes says. "This pit revealed a layer of residue at the bottom of the plow zone because there was no oxygen present there. That kept the residue from decomposing."
The corn roots in the moldboard-plowed field went down about 10 inches before hitting the plowpan, then turned horizontal as they tried to find cracks to go down deeper, she says.
There was limited structure in this field because of the compaction that extended across all four rows. In the disc-ripped field, the roots went down about 11 inches.
In the strip-tilled field, soil on the face of the pit crumbled more easily and was less dense.
In healthy soil conditions, corn roots can grow down 4 feet.
"Shallow roots pick up water and nutrients," DeJong-Hughes says. "Deep roots are mainly finding water. So in dry months, it's very important to be able to have the roots go deep," she says.
Fields that are strip-tilled and no-tilled will get better over time, she adds. It may typically take about 4 years for no-till soils to adjust, but it could take up to 7 years in northern Minnesota and North Dakota.
"There's been a concern that strip-tilled corn-on-corn will create problems because of increased levels of residue. But I've had strip-tillers tell me that after 4 years, there are either no residue issues or a lot less residue to manage," she says.
DeJong-Hughes attributes this to healthier soils that have better drainage and water infiltration, along with more oxygen and soil microbial activity.
Compaction Hangs On
Compaction is a hot topic in the Corn Belt after a spring where wet weather led to sloppy fields.
"I'm receiving a lot of questions from strip-tillers and other farmers about what they should do about ruts," DeJong-Hughes says. "Even in fields with good internal drainage that farmers strip-tilled or no-tilled, machinery got stuck.
"I suggest they till these ruts just enough to fill them in, but don't rip them. Soil structure is the No. 1 defense against compaction and tillage sets up your fields for even more compaction."
Even when ruts are filled in, the impact of compaction lasts a long time. After the wet fall of 2009, DeJong-Hughes says she saw seven fields where the ruts were filled in by disc-ripping or chisel-plowing.
The ruts weren't visible in the spring of 2010, but there were negative impacts. Corn planted on two rows of ruts yielded an average of 17% less than corn planted in two rut-free rows nearby.
DeJong-Hughes estimates the negative impact of ruts lasts about 3 years, and she notes that soybeans tolerate compaction and other problems much better than corn.
Strip-tillers who tile fields during the summer should level fields before strip-tilling in the fall. A strip-tiller told DeJong-Hughes that he regretted not leveling a tiled field before strip-tilling in the fall because the bumps in the field from tiling lasted for years.