University of Minnesota Extension (DeJong-Hughes et al., 2001)
Soil compaction reduces the total pores space of a soil, limited pore space is restrictive to air and water movement throughout the soil. Compaction can be caused by tillage, wheel traffic, crop rotation, or raindrop impact.
What to Look For?
Notice the platy nature of the soil structure, this is not ideal structure for water and air movement. Granular soil structure is a superior seed bed due to the pore space, nutrient holding capabilities and soil biology within those granular or aggregates *see the aggregation tab for more information* . The upper right photo displays the dense or massive nature of that compacted soil layer.
Tools to Determine Soil Compaction
Agricultural soils will likely be compacted to some degree due to field traffic. The level of compaction will vary by farm, soil type, and across a single field.
The shovel: simplest tool to assess compaction on-farm. Do you hit a layer of resistance as you dig? If so you have found a compaction layer, this will likely be at the depth of your tillage. The soil penetrometer is another tool that will give you a resistance reading for comparison.
Managing to Reduce Soil Compaction
Managing for reduced compaction includes: reduce traffic in wet spring, proper tire inflation, controlled traffic, etc.
From a soil health prospective crop choice is an option to build soil structure over time with diverse root systems and improve overall soil health. The key to this approach is to also reduce tillage, since each pass will break up soil structure in the zone of tillage.
Including multiple crops in rotation will provide the soil with different rooting systems. Cover crops are another option. Sunflower and turnip are examples of deep rooting crops that with start to build downward channels in the soil. Think long-term when trying to reduce soil compaction, it takes a many years to build soil structure but the benefits are great in terms of crop productivity and soil health.
Notice the deep taproot of the radish, large branching roots of the turnip and the small fibrous roots of a small grain. These very different root types together build soil aggregation.