Update from the Field: Compact Your Garbage, Not Your Soil
Posted by David Dyson, Agronomist on October 23, 2017
With the recent rains and soggy soils we have been seeing over the past week, compaction should be on everyone’s mind. The ever increasing size of tractors and equipment has led to compaction, resulting in limited yield potential. The extent of the problem depends on the type of soil compaction.
There are two types of compaction farmers must be aware of: topsoil compaction and subsoil compaction. Topsoil compaction is due to ground contact pressure only, whereas subsoil compaction is directly related to axle load.
Ground contact pressure is the pressure exerted by a tire or track on the soil surface, expressed in pounds per square inch (psi). Reducing contact pressures will result in less topsoil compaction. In completely flexible tires, surface contact pressure is similar to tire pressure. With most farm tires, surface contact pressure is about 1 to 2 psi higher than tire pressure due to stiffness in the tire. The best way to determine contact pressure is to calculate the load in pounds per wheel and divide it by the area of the tire that touches the soil (in square inches). This will give you the average contact pressure under that tire in psi. Research shows yields can be reduced by as much as 10% due to soil compaction in the top soil. This compaction can be easily remedied with tillage and the natural freeze and thaw cycle.
Axle load is the total load supported by one axle, usually expressed in tons or pounds. Farm equipment with high axle loads will cause deep compaction. Deep subsoil compaction can only partially be alleviated with subsoil tillage, and at considerable cost. Freezing/thawing and drying/wetting cycles have not been shown to improve soil compaction at this depth. Research shows yields can be reduced by up to 15% with this type of compaction and will last up to 12 years. This type of compaction should be avoided at all costs. Soils that are near or at their water holding capacity will act like a hydraulic ram and will drastically increase the chance of both surface and subsoil compaction.
Compaction, no matter how slight, can cause yield reduction. Keeping loads in the field as light as possible and driving on travel lanes will help in the majority of cases. Driving on saturated soils can lead to long term damage and yield reduction. I encourage my clients to stay off their fields during wet soil conditions. Deep soil compaction will restrict roots next year, which can in turn restrict water and nutrient uptake into the plant.
Summary:
- Make sure tires are properly inflated
- Calculate axle load, and try keep it under 7 tons
- Stay off of saturated soils
Figure 1: Keep axle loads under 7 tons
Figure 2: Studies show tracks don't necessarily prevent compaction
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Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at david_dyson@andersonsinc.com.
