Dave Nanda insisted on this picture showing the remnants of boot prints in the Corn Watch ’20 field in August. This year we implemented an emergence plot to study differences in corn plants based on when they emerge. The boot prints were made when I placed flags in muddy soil after a heavy rain on the first day corn decided to emerge. If the first plants aren’t flagged when they emerge, it defeats the purpose of tracking emergence until all plants come up.

“They were 6 inches deep in a few places, and they’re still hefty prints,” Nanda says. He is director of genetics for Seed Genetics Direct, sponsor of Corn Watch ’20.

“I wanted to document that they were still there in August because it shows that once soil is compacted, the compaction doesn’t go away quickly,” Nanda says. “And it doesn’t matter if soil compaction is created by a 250-pound man or a tractor weighing 10 tons or the planter disc forming the sidewall. Once it’s there, the impact on the soil can continue for a long time.”

Weather interaction

During a dry spell in early July, Nanda visited the field. Looking at a pair of flagged rows with boot prints between the rows, he could see corn plants at the V12 stage with lower leaves wilting. When he turned around and looked at the same rows in the opposite direction, where there were no boot prints, the leaves weren’t curling.

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“It was obvious compacted soil was affecting how well those plants could take up moisture,” Nanda says. “The plants where soil wasn’t compacted still looked normal.

It rained 1.5 inches over the next two days after that visit. Plants in the flagged area compacted by boot prints returned to a normal, healthy appearance.

“As long as there is ample moisture, the soil compaction won’t likely impact those plants more than it already has during early-season stress,” Nanda says. “Visible differences might occur if it turns dry again.”

Alleviating soil compaction

Soil compaction studies at Purdue University, the University of Minnesota and Ohio State University, most of them conducted decades ago, indicate that the impact of soil compaction created in one year can carry over into next season. In fact, if it’s severe enough, effects can be seen for two or more years.

When soil compaction was first recognized as an issue in the 1980s, many people assumed that freeze and thaw cycles would correct it over time. The same university studies indicate that while these cycles can eventually help break down compacted layers, they typically don’t help as quickly or as much as most people originally suspected. Even in locations where there are normally several freeze and thaw cycles during the winter, soil compaction can persist over time.

“I think we need to be on the lookout for signs of soil compaction every year when crops emerge,” Nanda says. “Sometimes patterns show up in crop growth, particularly in corn, that are hard to explain until you think back over traffic patterns during tillage and harvest for the past few seasons.

“These boot prints are just a graphic reminder that once you create soil compaction, plants must deal with the effects for a long time.”