Relationship between particle size summation curves and the moisture characteristic curve for soilless substrates
Soilless substrates are commonly composed from multiple components with each component varying in particle density, which can affect the meaningfulness or accuracy of gravimetric particle size distribution. The objective of this study was to compare volume or weight-based methods to determine particle size distribution of single [Douglas-fir bark (DFB) only], dual (DFB plus peat or pumice), or multiple component (DFB plus peat and pumice) soilless substrates. A secondary objective was to determine if existing model of Haverkamp and Parlange can be used to predict moisture characteristic curve of single, dual or multiple component substrates with known particle size distribution. Treatment design was a 3×3 factorial with three rates each of sphagnum peat moss and pumice (0, 15, and 30% by vol) added to DFB. Particle size distribution of the nine substrates was determined using volumetric (cm‑3) and gravimetric methods (g). The particle size distribution of each substrate was used to determine if an existing model could be used to accurately estimate a moisture characteristic curve for each substrate. There were statistical differences in particle size distribution between volumetric and gravimetric method. This resulted in a shift in the particle size summation curve (weight or volume based), however both methods remained strongly correlated providing equivalent information. Regardless of method used for measuring particle size distribution, we were unable to develop models to predict moisture characteristic curves from particle size data.
Zazirska, M., Owen, J.S., Altland, J.E. and Fields, J.S. (2021). Relationship between particle size summation curves and the moisture characteristic curve for soilless substrates. Acta Hortic. 1305, 209-218
bark, gravimetric, peat, pumice, particle density, volumetric water content