Sources and alleviation of compaction

In last week's post I broadly discussed how compaction happens (expulsion of air from pore spaces). This week I would likely to breakdown the various forms and sources of compaction in a little more detail as well as offering ways to ameliorate compaction in the field.

Two natural forms of compaction are recognized in soils, a fragipan, and a claypan. Both of these compaction layers serve to greatly reduce drainage in the soil profile. Ponding and long drying times are common in the Spring. Excess water drains slowly thus often delaying spring planting and with a limited root zone, low water supply to plants in rain-free periods in the growing season may be yield limiting. Claypan soils are mostly found in Missouri, Southern Illinois, Southern Indiana, and parts of Kansas. There are limited to no "corrective measures" to disrupt these compact layers that have formed over thousands of years of clay migration to the subsoil. Depth to the claypan ranges from 4-20". Some of the shallower claypans may be disrupted by tillage but quickly seal back after regular rainfall moistens the soil.

Fragipans are also formed without mechanical forces such as tillage or trafficking across fields. These soils are more common that claypan soils and comprise 12% of US soils. With the exception of a small area of Washington State these soils are found in the humid east. Fragipans are hard when dry and are thought to form over time through chemical and physical processes in the soil with translocated clay an important component to cement sand and silt particles together. Unlike claypan soils, soils with fragipans can respond to deep subsoiling. In a Pennsylvania study, corn yields were improved about 10% following deep tillage.

Plow pans also called tillage pans are something that can be successfully managed. Offset disks are the most compactive tool in the tillage tool portfolio. Think of what you are trying to accomplish with tillage and perhaps a vertical disk or field cultivator can be an alternative answer. The best way to deal with compaction is still to avoid causing it in the first place. When plow pans occur they can be broken with various levels of success using tillage tools such as deep rippers or subsoil-bedders. Subsoil-bedders operated just before planting in sandy Coastal Plain soils often creates openings that allow roots to access subsoil stored nutrients and water. These compact layers may reform during the crop season, suggesting that annual subsoiling may be necessary. Deep subsoiling on silt loam soils in the Upper South and Midwest maybe of some help, particularly if some soil fracturing can be accomplished in the fall after harvest. Using similar approaches in the spring is not typically a good practice as moist subsoil conditions reduce the fracturing effect and soil smearing and compaction might be an unwanted result.

Harvest-related ruts The key to reclaiming these areas is to make sure to allow them to dry before doing anything. Going back in the field too early will only exacerbate the problem. Some producers are successful in simply leveling the area at the correct moisture content in the spring and letting natural forces reform soil structure in the shallow subsoil.

Keeping narrow tires at the field edge and wide tires in the field is a way to reduce soil compaction

Mother Nature is your friend One of the more common practices following corn production in the Midwest is to use a chisel plow in the fall and let freeze-thaw/wet-dry cycles melt down the soil prior to Spring planting bed preparation. These natural cycles are more effective on silty soils with ample organic matter. Use of cover crops such as tillage radish can be another tool to fight shallow soil compaction

Coming next week: Handling this year's crop reside