Particle density of substrate components measured by gas pycnometer
The particle density (ρs) of a porous medium represents one of its basic physical properties. Understanding the ρs of a substrate allows for the most accurate calculation of total porosity (TP). However, there are difficulties in determining the ρs of organic compounds with traditional liquid pycnometer procedures. Direct ρs measurements were conducted on five substrate components (coir, peat, pine bark, perlite, and wood) using a helium gas pycnometer. This method resulted in consisted ρs measurements with low deviations. Coir yielded the highest ρs of the five materials at 1.47 g cm‑3. Peat and wood had similar ρs at 1.41 and 1.38 g cm‑3, respectively. Of the organic materials, pine bark yielded the lowest measured ρs at 1.29 g cm‑3. Perlite yielded the lowest ρs at 0.67 g cm‑3. Differences observed between particle density-derived TP and saturation method-derived TP could provide valuable insights with respect to substrate water capture and retention. Due to compounding errors with increasing bulk density, use of a single, generic ρs value for a component or a mix of materials to determine TP should be avoided. Further measurements of particle density should be made across a wider range of organic and inorganic components to reduce our reliance upon inconsistent techniques and unreferenced values.
Bartley, P.C., Amoozegar, A., Fonteno, W.C. and Jackson, B.E. (2020). Particle density of substrate components measured by gas pycnometer. Acta Hortic. 1273, 17-22
porous medium, helium gas pycnometer, saturation method