What is Soil Compaction?

Soil compaction reduces porosity and impedes water and nutrient flow and root growth. It is generally induced by man-made activities and often requires man-made actions to remediate. If compaction is left unchecked, it will have negative impacts on soil, root growth and plant development. Compaction is always a risk, but with proper management you can prevent its occurrence, which is always the goal in the first place.

Soil compaction reduces total pore space of a soil. It reduces the amount of large pore space, restricting air and water movement into and through the soil. Low soil oxygen levels caused by soil compaction often limit soil biological activity and root growth in affected soils.compaction

Soil compaction can develop in different ways. One of the most common is to tractor soils with heavy equipment when the soil is wet. Today’s farm machinery like combines, tractors, and grain carts weigh a lot, and when soils are wet, the particles slip and slide and compress together, compacting soil under their tire.

Tillage will also create compaction layers by shear forces that force soil down and to the side. For example a plow has a plow share that cuts and lifts the soil so it will turn. The plow share exerts downward forces causing a compaction layer at about an 8-inch depth. A concave disc blade on a tillage tool or a disc opener on a planter also creates sidewall shear forces. When planting in a wet soil, the disc opener will create sidewall compaction in the furrow that seedling roots won’t be able to penetrate.

Lastly, soil with low organic matter and/or poor biological activity will naturally become dense over time, no matter what the moisture levels are. Increased soil density is like compaction, however there is not a distinct compaction layer, just a general compression of the soil profile. A dense soil has less porosity, reduced water infiltration aeration, less water storage, less biological activity and reduced root growth.

If compaction occurs, farmers get out their ripper, a tool with a long shank that both fractures compaction layers and lifts and fractures density layers. Of course the key is to prevent it in the first place. For example, don’t till or traffic when the soil is wet. Reducing or eliminating tillage altogether reduces damage to soil structure.

When we improve soil health, that increases and strengthens soil structure so that it resists compression. That is why no-till farmers generally have an advantage.

At the end of the day, compaction can be measured with a penetrometer that measures the pressure to penetrate the soil or a measuring of bulk density. A compressed soil has greater density per volume of soil.

Soil treated with gypsum will eventually have a lower bulk density compared with untreated soil. The addition of organic amendments along with the application of gypsum can decrease bulk density even more. The softer soil is easier to till, and crops like it better. Adding organic amendments can also help by making the soil resistant to re-compaction.

Besides reducing or eliminating tillage, trafficking or tilling only when the soil is dry enough and building organic matter, routine application of gypsum can also improve structure of dense soils.

Gypsum will not eliminate compaction if it exists, but will help reduce its risk in the future.

What is your approach to handling compaction in your field or garden?