How To Test for Soil Compaction

Soil compaction occurs below the surface, so it's hard to spot. The best way to test for it is to probe the soil with a compaction tester to a depth of 36" to 48". The testing rod should move down through the soil with steady, even pressure. Hard, compacted soils resist penetration with the rod. Often penetration abruptly stops at a fairly uniform depth across a field or landscape area. This is referred to as "plowpan". For trees and shrubs, comparing root growth inside and outside the root ball is a quick way to tell if compaction is a problem. If you find evidence of compaction, dig to the depth indicated and check for abnormal root growth.

Soil compaction tools range from manual soil compaction rods to digital recording compaction meters. With a manual compaction rod, you can tell when you hit a hard compacted layer. Dial compaction probes tell you how much pressure (in pounds per square inch) it takes to penetrate the soil via a needle moving across a scale on the display. Digital compaction meters are similar to the dial probes, but they give you a digital reading and have the ability to record the depth and pressure for each test. No matter which tool you choose, make sure that the probe has depth markings so if you hit a compacted layer you will know how deep to go in order to correct the problem.