Is compaction an issue on your farm and is it limiting yield? Compaction limits root growth, soil porosity, water movement and water holding capacity and causes water ponding. And everyone knows that soybeans don’t like wet feet. Growth will stall and plants are vulnerable to root and stem rots. Unfortunately compaction can be created quickly, but it takes time to fully correct a breakdown in soil structure so it is better to prevent it from happening in the first place.

Compaction can be a layer or pan in the soil caused by tillage’s downward shearing forces or it can be compressed soil (increase in bulk density) caused by trafficking. Compaction layers usually settle in below 8 to 12 inches—below the depth of most tillage tools—while compression compaction occurs in the top 12 inches. These are different forms of compaction requiring different management practices. To see which type might be impacting your fields get a compaction probe with a digital readout.

I once probed some no-till fields on our family farm in Nebraska using a compaction meter that reads in psi (pounds per square inch) and indicates if you are in the green (0 to 200 psi, good), yellow (200 to 300 psi, warning) or red (greater than 300 psi, compacted). I probed down to 24 inches at 3-inch intervals and I was dismayed by the results. Both compression and pan compaction existed. From 0 to 6 inches the readings were in the green, from 6 to 15 inches most readings were in the yellow (compression compaction) and down at about 18 to 21 inches it shot into the red (pan compaction). My resolution:

• Manage compression compaction with no-till, cover crops and trafficking when soil was at the right moisture and add some alfalfa into the rotation.
• Manage pan compaction with one-time deep ripping and then prevent it from happening again.

Risk of compression compaction is greatest when the moisture content is near field capacity (24 hours after a soaking rain). If the soil is saturated, it is too muddy to work and the soil is difficult to compact because water fills pores. However slipping during trafficking of saturated soil will destroy soil structure. If you can ribbon the soil between your fingers 5 to 7 inches, it’s too wet. If the ribbon is 2 to 3 inches, it’s ideal since the soil profile will physically fracture.

Any tillage point or disc will create shearing forces and destroy soil structure. A plow share represents the best example of downward shearing forces that created a pan while lifting and turning the profile above. Concave discs shear (press down and to the side) and can compact the soil when wet. Tillage points on shanks can fracture the soil under ideal moisture conditions, but when too wet, shearing forces compact the soil.

Soil compaction is created by heavy wheel traffic and the shearing forces of tillage. There is no doubt that machines are bigger and heavier as farmers want to cover more acres in a narrower window. The bigger machines come with more weight (think 1200-bushel grain cart or 350- to 400-bushel grain tank) and bigger and more tires that enable farmers to traffic the soil when wetter than ideal. And with the window narrow in the fall or spring, they will till, plant or harvest in less than ideal moisture conditions.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.