A Comparison of Three Methods for Measuring the Density of a Forest Soil in New Zealand

Abstract

Three methods for measuring the density of a forest soil were compared: sampling with a traditional hand-held soil sampler and thin-wall (Shelby) tubes, and testing with a single-probe nuclear moisture-density gauge. An incremental approach was used when sampling with the nuclear gauge. Values of wet density for the soil layer between the source and the sensor were then recast for individual soil layers and converted to dry densities using the water contents provided by either the hand-held soil sampler or Shelby tubes. Shelby tube and nuclear gauge derived values of dry density were strongly related (R² = 0.80), values derived from the hand-held soil sampler and nuclear gauge less so (R² = 0.66). The nuclear gauge proved the most economical in use by a factor of about two, and data collection with the Shelby tube sampler and nuclear gauge was quicker when compared to the traditional hand-held soil sampler by a factor of about two. Sample compression associated with the Shelby tubes was corrected for when calculating the final density values. However, the degree of sample disturbance associated with the hand-held soil sampler was uncertain. The advantages and disadvantages of each method are discussed.

Keywords:

• hand-held soil sampler
• soil coring
• nuclear moisture-density gauge
• thin-wall sampler
• Shelby tubes