Gamma ray tomography measurements of soil density variations in soil cores

Small scale density variations in soil cores were measured and quantified using a gamma ray tomography scanner. The dry bulk density distribution was measured on samples of Norge silty loam (fine-silty, mixed, thermic Udic Paleustoll). The samples differed in size and sampling method. With these measurements the natural density variation within the samples and the effects of sample collection were defined on the scale of 5 mm3. Driven, 50.8-mm cores were adequate to describe the density variations of the soil matrix. None of the samples were considered adequate to define the soil macropores. The mean density distribution was found to vary over small vertical distances. All samples had density distributions with negative skew and kurtosis less than three. The standard deviation and kurtosis of the density distribution was found to increase with increasing numbers of macropores. (author)