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Corn+Soybean Digest

High-tech compaction measurement may be subject to misinterpretation

Soil compaction, "the silent thief" of crop yields, is often blamed when crops are struggling for no obvious reason, but a University of Missouri specialist cautioned producers not to rely on a high-tech "magic bullet."

"It's easy to blame soil compaction, but it's also difficult to quantify compaction," said Bill Casady, MU extension agricultural engineer. "You can't see it, you can't count it and you can't put a number on it just by digging. So you're looking for a magic bullet -- and the tip of a penetrometer does resemble a bullet."

Some producers are turning to soil penetrometers as a way to measure compaction in their fields. The device provides a quick reading of the force required to push the cone-shaped tip of the penetrometer into the soil.

"Unfortunately, the readings from a penetrometer are too easily misinterpreted," Casady said. "The latest fad is to take penetrometer readings and index them with GPS coordinates to make a colored map. In some cases, the map turns out to be bright red" - indicating severe soil compaction all across the field.

"Don't be alarmed until you dig deeper," he said. "Under higher soil-moisture conditions, that map might be green."

Because producers might believe compaction in their fields is far worse than it really is, "there's one bad idea that comes up once in a while, and that is: 'If we rip the soil, then if there's a compaction problem, we might get rid of it,'" Casady said. "It's not a good idea to adopt a blanket policy of ripping before doing the right tests. Ripping can do more harm than good."

Soil penetrometers have valid uses, he said, but "there are some publications circulating right now that might quickly dismiss the needed caution when using a penetrometer. We need to be cautious about the decisions we make from any soil physical property measurement."

Focus instead on "productivity and the bottom line," Casady said. "If you're sure you want to rip, I'll help you set up a statistically valid test to determine whether ripping pays under your particular set of circumstances and for your particular soil type."

Otherwise, "don't be alarmed by red maps," he said. "Call me after it rains, and we'll make a green map."

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