Wet field conditions during 2015 and 2016 disrupted many field operations and forced many activities to be performed when soil conditions were less than ideal. Traffic from tillage, planting, fertilizing, spraying and harvest activities can lead to soil compaction when soils are too wet. Soil compaction is the compression of soil volume, reducing the amount of pore space between soil particles. Reduced pore space limits movement and volume of air and water in the soil profile. Soil compaction can restrict root penetration, reduce water infiltration, reduce water and nutrient uptake and reduce yields for years. Yield loss can range from 5-30% depending on severity.
There are four types of compaction: surface crusting, surface compaction, tillage pan and deep compaction. Surface crusting is caused by the impact of raindrops on soils with weak aggregates. Surface compaction occurs near the surface within the normal tillage depth and is caused by any pressure applied to the soil surface. Surface crusting and surface compaction can generally be alleviated through normal tillage practices such as chisel plowing. Tillage pans and deep compaction develop below the normal tillage depth. Tillage pans develop when the same tillage depth is used year after year. Deep compaction is caused by axle load of field traffic (Figure 1). The severity of deep compaction is influenced by equipment weight, tire and axle number, tire inflation, soil moisture and number of passes. High axle loads from combines and grain carts can cause severe compaction.
The best approach is to prevent soil compaction from occurring. Tips for preventing compaction include:
• Avoid field activities if possible when soils are too wet.
• If working on wet soils, frequently empty combines and grain carts to reduce axle loads.
• Minimize traffic from tractor-trailers or other vehicles with high inflation pressure and small footprint.
• Reduce tire pressure, use floatation tires or tandem axles.
• Use smaller/lighter equipment when possible.
• Reduce axle loads below 10 tons.
• Control traffic patterns.
Alleviating deep soil compaction can be expensive and results are not guaranteed. Subsoiling may be required if compaction is obviously limiting yield. Subsoiling refers to tillage at a depth of at least 14 inches. Subsoiling should be performed to 1 inch below the compacted zone. Subsoiling should occur when the soil is dry enough for the compaction zone to be fractured. Subsoiling when it is too wet will not fracture the compacted layer. Excessive tillage or subsoiling can destroy soil structure making soil more susceptible to compaction in the future. Plans for preventing compaction are critical following subsoiling activites.
