Soil compaction is one of the biggest challenges we have when trying to grow crops on the highly weathered, low organic matter, sandy soils of the Deep South. 

Interestingly, it is the sandier soils that cause the worst problems. Soils high in clay and silt, such as those found in the Black Belt and Tennessee Valley region, are not as prone to compaction as are the sandier soils found in the Coastal Plain and Sandstone Plateau regions. 

The reason is because sand and clay don’t mix very well and most of our sandy topsoils have a subsoil that contains some clay. When clay is mixed with sand or vice versa, the clay tends to bind the sand particles together into something resembling concrete. 

The lack of organic matter makes the situation even worse. Tillage can aggravate the issue by mixing the sand and clay. Tillage when the soil is too wet really creates a problem. 

The following values came from the Master Gardener Handbook but illustrates the relative  compaction (force) that different activities can have on a soil.

• Person walking — 6 pounds per sq. inch;

• Crawler-type tractor — 12 pounds per sq. inch;

• Cow walking — 23 pounds per sq. inch;

• Horse walking — 40 pounds per sq. inch;

• Tractor with disk harrow — 150 pounds per sq. inch.

Recently, I’ve received a few questions about surface compaction in pastures and hayfields. Yes, it can occur, but is not as much a problem as in cultivated fields. 

When a pasture is over-grazed during wet weather, I’m sure some compaction occurs from the animals. Note that trails where cattle walk frequently have nothing growing in them.   

Likewise, if heavy equipment is pulled over a hayfield during wet weather, some soil compaction occurs. However, the good news is that plant roots, especially grass roots such as bahiagrass and bermudagrass do a terrific job of penetrating the soil and relieving potential compaction. As roots and rhizomes die and are replaced by new roots, organic matter is deposited and channels are opened up in the soil, resulting in a lower soil bulk density and less compaction.

Some have reported that bahiagrass is the best way of punching holes in a compacted soil.

Okay, so you suspect soil compaction is a problem in a pasture, hayfield, row crop, or garden. How can you be sure? Researchers have this device called a “pentrometer” which actually gives a measurement of soil strength when  pushed into a soil.