When it comes to field work, one thing is inevitable – COMPACTION.

Compaction is one of those bi-products of modern farming that is both unavoidable and also variable, depending on soil type, management practice, and weather conditions at the time of field entry.

A few remarks on soil compaction:

·       Compacted soils have reduced pore space, few overall larger pores, and a reduced rate of water infiltration; drainage [both surface and sub-surface] is reduced in compacted soil.

·       The top 2” – 5” of soil experience more than one freeze-thaw cycle per year [freeze-thaw cycles do little to reduce DEEP soil compaction].

·       Compaction impedes root growth, thus reducing the anticipated amount of root mass in the subsequent crop. The result is less root surface area for nutrient and water interception.

·       Yield losses are often driven by reduced water and nutrient uptake. If compaction is the cause of the issue, symptoms will appear worse in growing seasons with lower than average precipitation.

·       Plants spend energy by respiring at the root surface to take in nutrients. Respiration requires oxygen. If roots intercept nutrients in compacted soil, reduced aeration [pore space] can impede uptake of those nutrients. Potassium can be more affected than other nutrients.

·       Continuous tillage at the same depth with a disk or plow has been shown to create a compaction layer, sometimes called a “hard pan”. Studies indicate that even with vertical tillage, a “density layer” may persist which inhibits root growth – often this is known as “pancaking”.

Picture of pancaked roots in corn.

Picture of pancaked roots in corn.

·       Wheel traffic is the most significant source of compaction. As equipment has gotten larger, tire size has increased also. This helps to maintain a more constant PSI (pounds per square inch) load.

·       Larger axle loads from combines, grain carts, or silage wagons exert compaction deeper into the soil profile. On average, axle-loads no larger than 10 tons per axle keep compaction within the first 6” – 8” [a depth easily fixed with tillage].

·       Subsoil compaction is hard to alleviate. Many growers may not know that they have subsoil compaction – unless it is seen by a gate/entry point to the field. Compacted layers can persist for years and crops may not show stress from subsoil compaction unless other stresses from the growing season expose the underlying issue.

·       Subsoil compaction from heavy wheel traffic resulting in a “hard pan” can be found 12” – 18” into the soil profile. Floating vertical tillage implements into the compacted layer can help to fracture the “hard pan”, but when possible, tilling 1” – 2” below the depth of the “hard pan” is the best recommendation for alleviating these dense layers.

·       Subsoil density layers can be found using a penetrometer. A penetrometer measures the PSI [pounds per square inch] required to physically push through the soil profile.

Picture of soil penetrometer.

For more information on soil compaction [from mechanical operation], see THIS article from MN Extension.