Effect of Traffic and In‐Row Chiseling on Mechanical Impedance

A compacted layer at 0.15 to 0.25 m frequently occurs in soils of the southern Piedmont. This hardpan can be caused by disk or other tillage but the effect that wheel traffic may have in the formation of this layer has not been shown. The objectives of this study were to determine the extent traffic may contribute to hardpan formation, the effectiveness of shallow in‐row chiseling, and the possible correlation of the hardpan with a morphologically identifiable soil horizon. A long‐term tillage experiment where traffic had been controlled was examined at the end of its eighth year. The soil was a slightly eroded Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult). Summer crops of soybean [ Glycine max (L.) Merr. ‘Ransom’] and grain sorghum [ Sorghum bicolor (L.) Moench, DeKalb BR‐64] were double‐cropped with winter wheat ( Triticum aestivum L. Thell, ‘Coker 747’, 1979–1982, ‘Stacy’, 1983–1986). Spring tillage treatments consisted of disk tillage (DT), in‐row chiseling (IC), and coulter planting or reduced tillage (RT). All tillage treatments were disked in the fall before planting wheat. Cone index was measured in 1987 and 1988 in five positions relative to the row and showed that a hardpan was present in all positions at 0.15 to 0.25 m. The hardpan was a result of disk tillage and wheel traffic. Traffic caused compaction to a depth of 0.28 and 0.18 m in DT and RT, respectively. In‐row chiseling was effective in disrupting the hardpan to a depth of 0.26 m and contributed to significantly increased yields in grain sorghum. The hardpan coincided with the Ap2 horizon in this soil. The top of the Bt horizon may act to confine compactive stresses to the soil horizon above.