An Image-Based Method for Determining Bulk Density and the Soil Shrinkage Curve

Current laboratory methods for determining volume and bulk density of soil clods include dipping saran-coated clods in water (a destructive process due to the permanent coating), performing physical measurements on samples with well-defined geometries, or using expensive equipment and proprietary software (such as laser scanners). We propose an alternative method for determining the volume and bulk density of a soil clod, which is nondestructive, low cost, and utilizes free and open-source software. This method (the clodometer method) uses a standard digital camera to image a rotating clod, which allows reconstruction of its three-dimensional surface and subsequent calculation of its volume. We validated the method through comparison with the standard displacement method and then used the method to create a soil shrinkage curve for a silty clay loam soil. The method had acceptable precision (relative standard errors of the mean of 0.4-1.6%), which may be further improved through future software development.