Disks in wet soils: a recipe for compaction
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In many areas of Michigan, disks are the preferred secondary tillage tool. Any tillage tool has advantages and disadvantages and for disks, the largest concern is compaction. The nature in which disk blades contact the soil combined with their high level of downforce make these tools bigger culprits of compaction than shovel-tipped tools such as field cultivators. The risks for causing compaction increase dramatically in wet soil conditions like we are experiencing this year.
Tillage tools such as a chisel plow or field cultivator naturally dig into the soil. Their operating depth is controlled hydraulically and implement weight is partially carried by the wheels. A disk, in contrast, relies upon its weight to control working depth. In most cases, the wheels don’t carry much weight at all. In order for a disk to slice through residue, disks have beveled edges and high downforce. These properties mean that significant pressure is created where the blades make contact with the soil at the bottom of the furrow.
The nature of the tillage contact point in the soil can lead to subsurface compaction. Moldboard plows and disks are both notorious for the effects they have on soil properties. As a moldboard or an angled disk blade slides across the bottom of the furrow, a compacted layer or plow pan can form. These effects are amplified in wet soils as soil particles and aggregates are lubricated by water, enabling more compression of pore spaces. Moldboard plows have always been considered the bigger culprit of this effect, hence the term plow pan, but disks can create these compaction layers as well.
The effects of operating a disk in wet soil conditions can be seen in the accompanying images. Comparing the non-tilled (Photo 1) and disked (Photo 2) soil density at 6 inches deep, a noticeable difference in compaction can been seen. The tilled reading was taken between tire tracks, so this effect is a result of the tillage tool and not wheel compaction. Pans like this can restrict root growth, limiting the depth roots can penetrate. In severe cases of plow pan compaction, root penetration below the layer can be minimal, reducing the available soil profile from which roots can extract water and nutrients and limiting the degree plants are anchored in the soil.
Photo 1. Soil resistance in no-tilled conditions at 6 inches.
Photo 2. Soil resistance in freshly disked conditions at 6 inches.
While deeper tillage can easily take out a compacted layer formed by a disk, that won’t serve as much consolation to this year’s crop. If operating a disk this spring, make sure soil conditions are dry enough to avoid the formation of compaction layers. Soil type, soil moisture and disk setup will all effect compaction, so field to field assessment of conditions is often necessary. Disks are effective, efficient tillage tools, but like all tillage equipment, knowing and operating them within their limits is necessary to achieve optimum performance.
