Soil compaction: high-tech planters no substitute for walking fields

Soil compaction controlled where roots could grow and limited the ability of these corn plants to keep up with their neighbors.

May 16, 2023

Dave Nanda, Ph.D., SGD director of genetics, suspected what was wrong with the two small plants right away. To confirm he was right, he pulled out his trowel and began digging.

“You can learn many things about corn and corn production management walking fields early in the season,” Nanda said. He should know — he has been walking fields since the early 1960s as a plant breeder and an advisor.

“These two plants caught my eye because they were smaller,” he said. “When you see something out of the ordinary, ask questions. In this case, they could have been growing slowly for various reasons, including soil compaction.”

When the soil lifted out in a large chunk, the answer was obvious to Nanda. Soil compaction was so intense where these plants were seeded that it impacted their ability to emerge on time. That’s likely why they were smaller than neighboring plants.

“Look carefully at how roots are growing,” Nanda explained. “They’re trying to branch out and grow down, but it appears they’re following tiny cracks in the hard soil layers as they try to grow. Soil compaction limits rooting.”

When soil compaction forms in a hard layer, such as a plow pan, it may prohibit roots from growing downward so severely that they grow sideways instead. In extreme cases, plants later in the season may be easier to pull because most of their roots grew horizontally on top of the layer instead of penetrating to deeper depths. Because roots aren’t as deep as they should be, they won’t be successful in either anchoring the plant or pulling up as much water as the plant needs during hot, dry spells.

Why were two plants growing in very hard, compacted soil affected, while neighboring plants grew normally? According to Nanda, that’s a trademark of soil compaction. Soil composition and moisture levels in the soil vary across a field. Wheel track patterns also vary, especially in conventional tillage. Some areas receive more wheel traffic from one pass than other areas.

The inconsistency in soil compaction across a field produces the “tall corn, short corn” effect, a term coined when Gary Steinhardt, a Purdue Extension soil specialist, first began diagnosing soil compaction and calling it out in the early 1980s. Plants trying to grow where soils are more compacted often don’t get as tall as fast, producing the variation in crop size.

When plants are different sizes, investigate why. Was it traffic from the anhydrous ammonia application, tillage pass or planting pass? Were soils too wet?

“Figure out what adjustments you could make,” Nanda suggested. “It starts by walking fields, observing what is out of place and digging to investigate.”