The Impact of Sampling Methodology on Soil Bulk Density Measurement by the Clod Method

The clod method is a widely used and accurate bulk density method. However, its use is limited to sampling from soil pits. This study was conducted to: 1) determine whether clods collected from cores provide similar bulk density measurements to those collected from soil pits and 2) evaluate the impact of various clod bulk density methods on carbon stock calculation. Clods were collected from soil pits, 5.1 cm soil cores, and 8.9 cm soil cores. Three-dimensional laser scanning was used to measure the volume of the soil clods before and after oven-drying and bulk density was calculated as the dry mass of the clod divided by volume. Of 24 horizons sampled, 17 showed no significant effect of sampling method (core vs. pit) on dry bulk density. The error introduced by collecting clods from a core was small enough that it had no significant effect on carbon stock (p = .683). However, the moisture at which clods were scanned did have a significant effect on carbon stocks (p = .002 to 0.016). Data from the study suggest that collecting clods from soil cores introduces minimal error, but attention should be given to the moisture state at which clod volume is determined.