Submitted to: Midwest Soybean Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 12, 1996
Publication Date: N/A
Interpretive Summary: With the relatively wet soil conditions in many parts of the upper Midwest the past few years during planting and harvesting of soybeans, many farmers are finding soil compaction from the wheel traffic of farm machinery to be another production problem. This paper reviews several location-years of field research conducted in Minnesota addressing various aspects of soil compaction on soybean growth and yield. These data show that compaction o soil in the top 8-12 inches may not always be a problem. In relatively dry years, the surface compaction can help to conserve soil moisture and actually increase soybean yield. The opposite response was measured in relatively wet years. The dividing line for Minnesota conditions appears to about 15 inches of precipitation during the months of May through August. Farmers can use this rule of thumb to determine if surface soil compaction will likely be a problem in their situation. Deeper soil compaction, such as caused by very heavy harvest and transport equipment, does not seem to have a significant effect on soybean yield, but it may have a drastic effect on corn yield. Since corn and soybeans are often grown in rotation, the effect of heavy equipment during soybean harvest can adversely affect the following years corn crop. Significant corn yield decrease was measured 12 years after heavy harvest equipment compacted the soil to a depth of two feet. These field data provide guidelines to help farmers modify their field operations to minimize soil compaction, thus saving fuel, minimizing crop yield losses.
Technical Abstract: The major source of soil compaction in soybean production in the Midwest is the wheel traffic of farm machinery, especially when the soil is relatively wet and has a low bearing capacity. Wheel traffic of farm machinery with axle loads less than 5 tons (most tractors) will cause compaction mainly in the surface 30 cm of the profile. This paper reviews and summarizes the findings of 52 location years of field research in Minnesota on clay loam soils, studying the effects of compaction on soybean growth and yield. If the growing season (defined as May-August) precipitation is more than about 380 mm, soybean yields may be decreased by up to 20% as a result of compaction in the surface 30 cm of soil. If the precipitation is less than 380 mm, yields may be increased up to 40% by this surface compaction. These yield responses appear to be due mainly to soil water status rather than mechanical soil strength. If the axle load of the field machinery is more than 10 tons, bulk density, hydraulic conductivity and penetrometer resistance can all be significantly changed to a depth of 60 cm. These changes in deep soil conditions appears to be more detrimental for corn growth than for soybeans, probably because the later has a tap root system. Since corn and soybeans are commonly grown in rotation, subsoil compaction during soybean harvest can be important, even though it may not adversely affect soybean production itself. These data are useful in developing guidelines for farm managers using heavy farm machinery so as to avoid or minimize the detrimental effects of soil compaction while at the same time taking advantage of the time-savings aspects of large equipment.