Soil pits can help no-tillers answer questions about crop development, compaction and soil quality.
Three experienced scientists say soil pits are another tool no-tillers can use to examine soil structure, root development, compaction, soil quality and other important agronomical issues.
These pits might even reveal information that wouldn’t be obvious through soil tests, making it easier for no-tillers to solve yield-robbing problems.
“They can see if there were many shallow roots if the soils were wet,” says Mike Petersen, Orthman Mfg. Co.’s agronomist. “How deep did the corn roots go? Did the corn roots go down deeper when it was dry in August and September? How did the corn finish?
“A soil pit can also tell you about seed placement, and whether the corn extracted moisture late in the season so the crop could finish well,” he adds. “The difference between extracting the moisture from deep in the soil can be 150 bushels per acre vs. 200 bushels per acre.”
Jodi DeJong-Hughes, University of Minnesota Extension crops and soils educator, says soil pits allow growers to assess the impact of management practices in a way that might not be possible with soil tests.
“These impacts — particularly compaction — will show up in root-resistance areas,” DeJong-Hughes says. “With a knife, dig across the top layer of soil in the pit. If there is good soil structure, the soil should fall off in your hand. Wheel traffic will show up as a U-shaped impression about 8 inches below the surface.”
DIGGING FOR CLUES. NRCS soil scientist George Derringer, speaking here at the Ohio No-Till Council’s Field Day last year on Keith Kemp’s farm, says soil pits can help no-tillers answer questions about problems ranging from compaction to weak cornstalks.
Petersen recommends digging a soil pit at least 150 to 200 feet into a field, avoiding areas with steep slopes or compaction issues — unless compaction is a concern. Dig the pit perpendicular to the rows, and then dig a trench to walk down into the pit.
DeJong-Hughes recommends that no-tillers dig two soil pits — one on top of a hill and another at the bottom — so they can compare and contrast soil and roots.
“This is particularly helpful when there’s green and yellow corn side by side,” she says. “Dig a pit that goes across the soil with the green-and-yellow corn and find out why.”
There are trouble signs to look for in the walls of soil pits, Petersen says. These include roots that flatten out, wrap up in a barrel, or “stair-step” to go deeper in the soil.
“Pull out a golf-ball size piece of soil,” Petersen says. “Can you see any soil pores? These pores are about the size of the tiny pores in your skin.
“Ground that’s been squeezed by tires will be so dense that it will not have pores. Look for this in the top 12 inches of the soil. If there are no roots below 12 inches, the soil is compacted.”
Soil pits also allow no-tillers to examine soil quality, says George Derringer, an NRCS soil scientist from Ohio. “You’ve got to have more than a good volume of organic matter in the soil,” Derringer says.
“You need a diversity of sources of organic matter, which includes good populations of mycorrhiza fungi, which hold the soil aggregates together so they retain their shape throughout the wetting and drying cycles in the soil.
“Stable soil aggregates enhance the retention of nutrients in the soil and open numerous pathways for root development and air and water movement in the soil,” he adds.
Maximizing soil quality for crop production requires greater diversity of soil organisms, which follows more diverse plant residues, Derringer says.
“Many producers are learning the art of enhancing soil life through various, deep-rooted cover crops which open more numerous pathways for crop root develop- ment,” he says.
“Cover crop legumes, tillage radishes and numerous other crops grow soil biology below ground after crop harvest and build underground reserves to bring forth its treasure next season.”
Digging a pit can be relatively straightforward, but some safety basics should be followed.
“It’s smart to call a utility-locator service 7 to 10 days before you want to dig the soil pit,” Petersen says. “In most places, they will come out and locate the utilities within 3 days.
“When looking for compaction and digging soil pits in an end row, be careful of power lines, drains, electrical lines and gas lines. Stay out of that area. Go in between your tile lines.”