Rushing to the field when the soil is wet can increase chances for severe soil compaction combined with the weight of equipment and traffic pattern in the field. Conducting field operations during wet field conditions compounds the amount of compaction occurring, an Iowa State University soil specialist says.

"Maximum soil compaction occurs when soil moisture is at or near field capacity because soil moisture works as a lubricant between soil particles under heavy pressure from field equipment," Mahdi Al-Kaisi says.

Compaction within the top 3 to 6 inches of the soil is generally associated with the amount of surface pressure, Al-Kaisi says. Compaction below that is primarily associated with axle weight. For example, if soil a foot below the surface is at field capacity and the tractor's axle load is 7 to 8 tons or greater, compaction can occur at this depth, despite lower surface pressures.

Indications of soil compaction during and immediately following a normal rainfall include slow water infiltration, water ponding, high surface runoff and soil erosion. Additionally, Al-Kaisi says soil compaction can be diagnosed by stunted plant growth, poor root-system development and potential nutrient deficiencies (i.e., reduced potassium uptake). These soil compaction symptoms are a result of increased bulk densities that affect the ideal proportion of air and water in the soil.

The most efficient way to verify soil compaction is to use a tile probe, spade or penetrometer to determine a relative soil density. Soil moisture conditions can have a significant effect on penetration resistance, he adds.

"For example, in dry soil conditions, soil penetration resistance is much higher than wet conditions because soil water acts as a lubricant for soil particles," Al-Kaisi says. "Therefore, it's wise to determine soil compaction early in the season or compare observations and measurements from suspected areas with adjacent areas that have little chance of soil compaction due to traffic patterns.

Management Decisions

Al-Kaisi says the most effective way to minimize soil compaction is to avoid field operations when soil moisture is at or near field capacity. Soil compaction will be less severe when soil tillage, fertilizer application and planting operations occur when the field is dry. Soil moisture can be determined using a hand ball test or observing a soil ribbon test.

Second, properly adjust tire size and air pressure. He says larger tires with lower air pressure allow for better flotation and reduce load on the soil surface. Additionally, using larger tires that are properly inflated increases the "footprint" on the soil.

Third, use the same wheel tracks to minimize the amount of land traveled across. Most damage occurs with the first pass of the implement. Using controlled traffic patterns can be done effectively by using implements that are the same width for planting, spraying, harvesting and more.

Top 10 Reasons to Avoid Soil Compaction
1. Causes nutrient deficiencies
2. Reduces crop productivity
3. Restricts root development
4. Reduces soil aeration
5. Decreases soil available water
6. Reduces infiltration rate
7. Increases bulk density
8. Increases sediment and nutrient losses
9. Increases surface runoff
10. Damages soil structure