Efficiency of Four Tools for Measuring Soil Bulk Density or Strength

Miller, Richard E.; Hazard, John; Howes, Steven. 2001. Precision, accuracy, and efficiency of four tools for measuring soil bulk density or strength. Res. Pap. PNWRP-532. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 16 p. Monitoring soil compaction is time consuming. A desire for speed and lower costs, however, must be balanced with the appropriate precision and accuracy required of the monitoring task. We compared three core samplers and a cone penetrometer for measuring soil compaction after clearcut harvest on a stone-free and a stony soil. Precision (i.e., consistency) of each tool at depths of 0-10, 10-20, and 20-30 cm was determined from two adjacent samples at 21 or more sampling points in each harvested location. Because one bulk density (D b ) sampler provided a continuous sample of each decimeter depth, it was designated as the standard; thereby, the relative accuracy and bias of the two shorter core samplers could be calculated. Both shorter samplers overestimated D b as determined by the standard. At least 15 penetrometer samples could be taken and processed in the time required for three D b samples to the same 30-cm depth. Precision of measurements taken by the cone penetrometer, however, was clearly less than that with any of the D b samplers. Based on time requirements and precision of each tool, we examined the efficiency of double sampling (using a combination of penetrometer and core sampler) for estimating D b . Results from the stone-free soil indicated an advantage in both precision and efficiency in applying double-sampling theory to estimate D b rather than sampling exclusively by the more time-consuming core samplers.