Soil compaction: What can you do?
As spring approaches, plan to include strategies that reduce soil compaction. Soil compaction concerns have been growing in Minnesota as annual precipitation and the size of farm equipment have dramatically increased.
Wet soils are particularly susceptible to compaction. Heavy equipment and tillage implements amplify damage to the soil's structure, decreasing pore space and limiting soil and water volume even further. Improving soil structure is the best defense against soil compaction. A well-structured soil holds and conducts water, nutrients, and air necessary for healthy plant root activity.
Myths about soil compaction
Don't be fooled by two very common and widespread myths about soil compaction: 1) Freeze-thaw cycles will alleviate a majority of the soil compaction created by machinery, and 2) What compaction "Mother Nature" does not take care of, deep tillage or subsoiling will.
A combination of heavy axle loads and wet soil conditions increases the depth of compaction in the soil profile. For example, a load of 10 tons per axle or more on wet soils can extend compaction to depths of two feet or more. Since this is well below the depth of normal tillage, the compaction is more likely to persist compared to shallow compaction that can largely be removed by tillage.
Although soils in this regions are subject to annual freeze-thaws cycles and freeze depths of 3 feet or more, only the top 2 to 5 inches will experience more than one freeze-thaw cycle per year. The belief that freeze-thaw cycles will loosen compacted soils may have developed years ago when compaction would have been relatively shallow. At that time, machinery weighed less and grass and deep-rooted legumes were grown in the crop rotation.
However, compaction can be alleviated to a limited degree in excessively dry soils. In very dry soils, cracks will form in most Minnesota soils. Considered a natural tillage tool, these cracks will break up compaction, but only to the depth of the crack.
While deep tillage (greater than 18 inches) is capable of shattering hard pans created by wheel traffic, it has not been proven to increase yield consistently or for a long period of time. In the Midwest, research results have shown few positive yield responses to subsoiling. When responses do occur, they are relatively small and variable. Predicting the effects of subsoiling is difficult due to soil differences, degree of subsoil compaction, soil moisture, future traffic, weather conditions, crops grown and tillage methods.
Tire inflation pressure (psi) versus axle load
Tractors equipped with either tracks or tires can both create surface compaction. Which, however, creates the least amount? In fact, if radial tires are properly inflated, both tires and tracks will create similar amounts of surface compaction.
Compaction created by smaller tractors (less than 10 tons per axle) usually remains in the top 6 to 8 inches and can be alleviated by tillage. In contrast, an increasing number of tractors, full combines, slurry tankers and grain carts can weigh between 18 and 40 tons per axle. This equipment, whether equipped with tires or tracks, can compact the soil to depths of 3 feet.
Tracks exert a ground pressure of approximately 4-7 psi depending on track width, length, and tractor weight. Radial tires, on the other hand, exert a pressure of 1 to 2 pounds higher than their inflation pressure. For example, if a radial tire is inflated to 6 psi, the tire exerts a pressure of 7 to 8 psi on the soil. Assuming that loads and soil pressures are similar, both tracks and tires will exert similar stress onto the soil.
One of the most important factors for decreasing soil compaction potential is to stay off the soil when it is wet. Unfortunately, this is not always possible, as planting opportunities are often limited. Other effective strategies include maintaining proper tire inflation rates and decreasing axle loads. Radial tires can be inflated as low as 6 to 8 psi, but producers should check with their tire dealers to confirm proper tire pressures. Frequently checking and maintaining proper pressures will not only help reduce soil compaction, it will improve tractor efficiency
Inflating tires to the proper air pressure will reduce surface compaction, while reducing axle loads will reduce the depth of compaction. These strategies help maintain a well-structured soil, one of the most important factors when growing a healthy crop. Preventing soil compaction enhances water infiltration and storage capacity, timeliness of field operations while decreasing plant root stress and disease potential.
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