Contribution of water content and bulk density to field soil penetration resistance as measured by a combined cone penetrometer–TDR probe

Abstract

Soil strength as measured by cone penetrometers depends on several parameters, but it is mostly affected by the soil water content ( θ) and bulk density ( ρ). In order to better understand the effect of the water content and bulk density on soil strength we developed a combined penetrometer–coiled TDR probe to determine simultaneously the depth distribution of penetration resistance and water content in a soil profile. Field experiments carried out for a Yolo soil allowed the fitting of the effect of θ and ρ using a combined power–exponential equation. Using the combined cone penetrometer–TDR probe data, the fitted equation may be used to estimate soil bulk density.