Jodi DeJong-Hughes, Extension educator
Minnesota has experienced an extremely wet year. As of September 12th, Minneapolis has had the second-wettest year in weather records. It is no wonder that growers are concerned about harvest equipment causing ruts and compacting the soil.
The plant population was not statistically different between rutted and non-rutted areas, but the non-rutted corn was 8.5 inches taller and was one growth stage ahead of the rutted corn (V10.4 versus V9.1).
In the fall, the observation areas were hand-harvested and final population, grain moisture and corn yield were determined. Final plant population and grain moisture were not affected by the rutted soil. However, yield was decreased 28 bushels an acre (159 versus 131) where the field had been rutted.
The rutted areas had a 17-percent yield decrease that was fairly consistent across the seven sites. The same number of ears were gathered (same population), but the differences in ear length, diameter and kernel fill were easy to see.
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.
How do ruts affect yield?
To find the answer, UMN Extension Educator Jodi DeJong-Hughes and private consultant Frenchie Bellicot performed GPS analysis on seven pairs of ruts and neighboring non-rutted area in four fields near Clarkfield, Minnesota. Six of the fields were fall chisel-plowed with spring field cultivation and one field was fall disk-ripped and spring field-cultivated. In the spring of 2010, the observation areas were flagged. Corn height, population and growth stage were tracked during the growing season.The plant population was not statistically different between rutted and non-rutted areas, but the non-rutted corn was 8.5 inches taller and was one growth stage ahead of the rutted corn (V10.4 versus V9.1).
In the fall, the observation areas were hand-harvested and final population, grain moisture and corn yield were determined. Final plant population and grain moisture were not affected by the rutted soil. However, yield was decreased 28 bushels an acre (159 versus 131) where the field had been rutted.
The rutted areas had a 17-percent yield decrease that was fairly consistent across the seven sites. The same number of ears were gathered (same population), but the differences in ear length, diameter and kernel fill were easy to see.
How can I reduce compaction?
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 infiltration 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.Does deep tillage help?
While deep tillage (greater than 12 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.
Management strategies
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 harvesting 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 efficiencyFor more information
For more detailed discussions on soil compaction, see z.umn.edu/FullCompaction and z.umn.edu/SoilVideos.
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