For example, a load of 10 tons per axle or more on wet soils can extend compaction to depths of two feet or more. At that time, machinery weighed less and grass and deep-rooted legumes were grown in the crop rotation.Ĭombining heavy axle loads and wet soil conditions increase compaction’s depth in the soil profile.
The belief that freeze-thaw cycles loosen compacted soils may have developed years ago when compaction would have been relatively shallow. Soils with a higher percentage of clay and silt, which naturally have more pore space, have a lower bulk density than sandier soils.įigure 2: Cracks that form in a dry soil.Īlthough soils in the Upper Midwest are subject to annual freeze-thaw cycles and freeze depths of three feet or more, only the top two to five inches will experience more than one freeze-thaw cycle per year. As the pore space decreases within a soil, the bulk density increases. One way to quantify the change is by measuring the bulk density. Soil compaction changes pore space size, distribution and soil strength. Finally, while soil compaction increases soil strength – the ability of soil to resist being moved by an applied force – a compacted soil also means roots must exert greater force to penetrate the compacted layer.įigure 1: Effects of compaction on pore space. In addition, the exchange of gases slows down in compacted soils, causing an increase in the likelihood of aeration-related problems. This happens because large pores more effectively move water downward through the soil than smaller pores. Heavily compacted soils contain few large pores, less total pore volume and, consequently, a greater density.Ī compacted soil has a reduced rate of both water infiltration and drainage. Soil compaction occurs when soil particles are pressed together, reducing pore space between them (Figure 1). A well-structured soil holds and conducts the water, nutrients and air necessary for healthy plant root activity.
Improving soil structure is the best defense against soil compaction. Heavy equipment and tillage implements amplify damage to the soil's structure, decreasing pore space and limiting soil and water volume even further. Wet soils are particularly susceptible to compaction. Soil compaction concerns have been growing in Minnesota as both annual precipitation and farm equipment size have dramatically increased.
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