2018 ASHS Annual Conference

The total porosity of substrate components can be derived from indirect measurements such as the North Carolina State University Porometer Method (PM), a saturation method, or calculated from its bulk volume divided by its particle density (ρ_s). In order to calculate substrate total porosity from ρ_s, coir, peat, pine bark, perlite, and wood fiber components were analyzed using a helium gas pycnometer. Porometer Method data was collected from the NCSU Horticultural Substrates Lab’s database on single component substrates and compared to the calculated total porosity derived from ρ_s. The PM’s measured total porosities were consistently lower than the derived total porosity determined by ρ_s. However, it was observed that the initial moisture content of the substrate prior to being subjected to the PM affected the agreement between the two methods. Assuming the ρ_s derived total porosity provides the true value, the optimal moisture content to achieve the most accurate results from the PM could be determined for each material.