How To Test for Soil Compaction

A few minutes in the field can help you diagnose a costly, yield-robbing problem that may be invisible on the surface.

By Marilyn Cummins

To check for sidewall, surface and tillage pan compaction, dig with a spade, shovel, hand trowel or knife to examine the soil characteristics in the furrow, on the soil surface and the top few inches of soil.

To check deeper for resistance or compacted layers, insert a soil probe, tile probe or even the wire of a marking flag slowly into the soil in several areas of the field, feeling the force needed to push into the soil and recording the depths where you feel resistance or where the flag wire starts to bend. Best to do this in wet soil in the spring or fall, rather than in dry soil that inherently resists penetration, and include a spot in an uncultivated fencerow for comparison.

Another method is to dig a small trench down 2 feet across the crop row, starting with one end of the trench in an area free of wheel traffic so you can compare suspected compacted areas with less-compacted areas. Every 2 inches down the side of the trench from the surface, use a screwdriver or knife to see how much force it takes to penetrate the trench sidewall. If a crop is growing, examine the root growth pattern and development, watching for a lack of lateral growth where there is wheel-traffic compaction.

A tool called a cone-tipped penetrometer takes numerical readings of the force required to penetrate layers of the soil, letting you compare areas of compaction to each other and with less-compacted areas of the field. Jason Lee, AGCO agronomist for North America, used penetrometers in the 2020 Fendt® Momentum™ Crop Tour plots to gather and study compaction data from treatments using different tire pressures and weight-management settings. His tips for best results when using a penetrometer include:

  • Have one person using the same rate of push take all the readings in a field to keep data consistent.
  • Take readings a day or two after a moderate rain or when soil moisture is consistent across the field.
  • If comparing treatment differences, it’s good to test and compare areas with the same soil type, drainage and topography.