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A case study in soil compaction and weather stress

Corn Watch: This slideshow showing the impact of rain on compacted corn illustrates why soil compaction is an elusive enemy.

If a picture is worth a thousand words, then several pictures illustrating a classic case of the effects of soil compaction and how rain alleviates it saves several thousand words. It’s a true concept — just look at this slideshow.

Here’s the back story: When setting up an emergence monitoring project as corn first popped out of the ground in May, the soil was so saturated after a heavy thunderstorm that just walking in the field to place flags next to plants created soil compaction. Boot prints were as deep as 6 inches, especially between a couple of rows in the project.

To monitor which plants emerged on which day and later impacts on plant development, the goal was to place a different color of flag by each plant the day it emerged in 1/1,000 of an acre, or 17 feet, 5 inches of 30-inch-wide corn rows. Ten rows were selected, and 1/1,000 acre of each one, all side by side, were flagged.

It was so wet when those first flags were placed that a rubber boot slipped off, sucked down into the mud.

Soil compaction impact

Dave Nanda visited the field July 7. He is director of genetics for Seed Genetics Direct, sponsor of Corn Watch ’20. The field was very dry, and it was in the middle of a string of days hitting above 90 degrees F. Some replanted corn in the field showed moisture stress.

Standing at the edge of two rows in the emergence plot, Nanda observed that lower leaves in both rows were curling, beginning to show the impact of moisture stress. He had already determined plants were at the V12, or 12th-leaf, growth stage.

Simply turning around and looking at the same rows, not flagged or tracked up with human boot prints, he saw no rolled or curling lower leaves.

“It was quite obvious,” Nanda says. “We normally think of creating soil compaction with heavy machinery, or perhaps creating sidewall compaction with the planter, but the boot prints from a large man created soil compaction, too. Those plants don’t know what created the soil compaction. They just sensed that their roots were affected, and if moisture was limited, they couldn’t supply as much moisture as might be necessary.”

Night and day

Here is the kicker. Later that day after Nanda’s visit, 0.5 inch of rain fell on the field. The next afternoon, about 1 inch was received. By the morning of July 9, the moisture had worked its magic. Less than 48 hours after Nanda saw the impacts of moisture stress, especially on compacted spots and younger plants, it looked like a different field.

Standing in the same spot in the emergence plot as two days earlier, looking down the same rows, corn leaves were no longer curled. They were fully open. Looking the other direction, plants looked fresh and healthy, as well.

Gary Steinhardt, Purdue University Extension soil specialist, notes that how much impact you see from soil compaction on corn depends heavily upon the environment, particularly rainfall amount and timing. Rain at the right time can mask the effects of soil compaction. However, the soil is still compacted.

This story isn’t over, Nanda explains. Weather conditions during the rest of the season will determine whether plants show signs of stress related to soil compaction again.

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