Compaction and Soil Structure Modification by Wheel Traffic in the Northern Corn Belt

Abstract Increasing size and weight of farm tractors is causing increasing concern about soil compaction. Controlled wheel‐traffic studies in Minnesota on a silty clay loam showed that wheel traffic of normal farming operations could compact the soil to a 45‐cm depth. Penetrometer resistance was a more sensitive indicator of soil compaction than was bulk density. Wheel traffic increased soil bulk density by 20% or less, whereas penetrometer resistance was increased by as much as 400%. Fall tillage essentially alleviated bulk compaction in the 0‐ to 15‐cm layer. Plowing was more effective than disking or chiseling in decreasing compaction in the 15‐ to 30‐cm layer. Compared with plowing, bulk density and penetrometer resistance values for chiseling or disking were about 5 and 40% higher, respectively. Compaction below the tillage depth was not completely ameliorated by annual freezing and thawing. Wheel‐induced compaction was more persistent in individual soil structure units than in bulk soil. Strength and density of wheel tracked clods were greater and average aggregate diamter was larger than that of nontracked clods, a difference which persisted overwinter.