If you were forced to harvest wet fields in 2018, odds are higher that soil compaction could be a bigger factor in 2019. However, that doesn’t mean you need to panic, Gary Steinhardt says.

One factor determining if you see a yield impact is which crop you grow, Steinhardt says. He’s an Extension soil scientist at Purdue University.

“You aren’t as likely to see a yield impact in soybeans,” Steinhardt says. “When we compacted soils on purpose, we didn’t see a yield decrease in soybeans, even where soils were severely compacted.

“Sometimes soybeans would look tough. Yet soybeans have a tremendous ability to compensate. When the combine went through, we didn’t see a difference.”

That wasn’t always true for corn, he cautions. Sometimes soil compaction can cause a significant yield reduction in corn.

“If there’s plenty of moisture, you’re not as likely to see a big effect,” he says. “If it’s warm and dry, soil compaction can impact corn more because it affects root development.”

Find soil compaction
Soil compaction is typically not uniform. That was the major explanation when “tall corn, short corn” was first diagnosed nearly 40 years ago. It’s likely to be especially true this season in rutted fields. However, you don’t have to see ruts to have soil compaction.

“If soils were at field capacity, you could have caused serious soil compaction even without rutting,” Steinhardt says. “The same thing can happen in no-till. Just because you don’t make tracks doesn’t mean you’re not creating soil compaction.”

These pictures show what can happen moving a short distance within a soybean field. A soil penetrometer helped detect soil compaction.

There are two colored rings on the dial. The inner ring corresponds to where the one-half-inch steel tip used in these examples is attached.

MINIMAL SOIL COMPACTION: Soil compaction often varies within a field. Note that the penetrometer gauge is in the green for the inner ring, indicating less soil compaction in this spot.

In the middle of the field, there was little resistance to pushing, and the needle was in the green. That could indicate minimal soil compaction.

Near the end rows, the dial went into the yellow. There was some resistance to pushing.

MODERATE SOIL COMPACTION: Note that the pointer is in the yellow on the inner ring of the dial. That indicates the penetrometer is picking up some resistance to pushing through the soil.

On the end rows, the needle went into the red before the penetrometer pushed through a resistance layer. That likely indicates a definite compacted layer.

It’s not unusual to find soil compaction on turn rows, Steinhardt observes.

HARD LAYER: The person pushing the penetrometer moved just a few feet and found this hard spot. The needle on the dial in the inner ring is in the red, meaning the penetrometer is tougher to push.

He cautions that numbers and colors on a soil penetrometer dial are relative. Whether the soil is dry or wet can influence which colors the needle lands on.

A tile probe can also help you detect layers of resistance, he adds. A penetrometer is useful if you don’t put too much emphasis on numbers and colors, he concludes.