Soil compaction negatively influences many important soil functions, including crop growth. Compaction occurs when the applied stress, σ, overcomes the soil strength. Soil strength in relation to compaction is typically expressed by the soil precompression stress, σ pc. Deformation is assumed to be elastic and reversible as long as σ ≤ σ pc. This work examined soil stress-strain behavior as measured in situ during wheeling experiments and related it to the stress-strain behavior and σ pc measured on soil cores in uniaxial compression tests in the laboratory. The data analyzed were from a large number of wheeling experiments carried out in Sweden and Denmark on soils with a wide range of texture. Contradicting the concept of precompression stress, we observed residual strain, [Latin Small Letter Open E] res, at σ ≤ σ pc. These observations were supported by stress-strain data measured in uniaxial compression tests, which likewise showed [Latin Small Letter Open E] res > 0 at σ ≤ σ pc. Residual strain was observed in the field when σ exceeded approximately 40 kPa, and when the ratio σ/σ pc exceeded roughly 0.1, although [Latin Small Letter Open E] res was very small at σ/σ pc < 0.5. These values were similar to those obtained on confined uniaxial compression curves. On the basis of our findings, we question the use of σ pc as a measure of soil strength and call for a reevaluation of the precompression stress concept.
1Agroscope Reckenholz-Tänikon Research Station ART, Department of Natural Resources and Agriculture, Zurich, Switzerland.
2Swedish University of Agricultural Sciences, Department of Soil & Environment, Uppsala, Sweden.
3Aarhus University, Department of Agroecology, Research Centre Foulum, Tjele, Denmark.
4Bern University of Applied Sciences, School of Agriculture, Forest and Food Sciences, Zollikofen, Switzerland.
Address for correspondence: Thomas Keller, Agroscope Research Station ART, Reckenholzstasse 191, 8046 Zürich, Switzerland; E-mail: email@example.com
Financial Disclosures/Conflicts of Interest: None reported.
Received December 23, 2011.
Accepted for publication May 31, 2012.