Soil formation and organic matter accretion in a young andesitic chronosequence at Mt. Shasta, California

Soil water content is an important factor in making decisions about cultural operation because of its effects on soil compaction by agricultural machines. We report an investigation of the effect on soil water content at wheeling on compaction in the tilled layer. The model of compaction proposed by OʹSullivan et al. (Soil Tillage Res. 49 (1999) 325) is used to simulate field wheeling experiments conducted in calcareous and loess soils in the northern France at seedbed preparation for a wide range of soil water contents. The model estimates the dry bulk density under the centerline of a wheel track from tire characteristics and the soil mechanical parameters measured in triaxial tests. The comparison with field data shows that the model can simulate trends observed in the field namely increases in dry bulk density and rut depth with soil water content. An analysis of model sensitivity indicates that quantitative differences between model output and experiment can be attributed to difficulties in assessment of mechanical parameters. They also may be due to omission of lateral displacement in the model.