Assessment of substrate physical properties in bark- and peat-based stratified substrate systems

Authors: FIELDS, JEB - Louisiana State University Agcenter; CRISCIONE, KRIS - Louisiana State University Agcenter; Owen Jr, James - Jim

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2024
Publication Date: 11/20/2024
Citation: Fields, J.S., Criscione, K.S., Owen Jr, J.S. 2024. Assessment of substrate physical properties in bark- and peat-based stratified substrate systems. HortScience. 59(12):1823-1827. https://doi.org/10.21273/HORTSCI18188-24.
DOI: https://doi.org/10.21273/HORTSCI18188-24

Interpretive Summary: Soilless substrate stratification is increasing in popularity in the nursery and greenhouse industry globally. With substrate stratification becoming more prevalent in both the U.S. and global horticultural markets, it is important for scientists to evaluate physical properties of stratified system in a consistent, objective, and standardized manner. The aim of this research was to augment the established, conventional NCSU porometer method to ascertain accurate measures of substrate physical properties in a controlled laboratory assessment. To do this, individual 7.6 and 15.2 cm tall cores (7.6 cm i.d.) and vertically stacked to more accurately reflect stratified substrates in containers (i.e., 50:50 top:bottom ratio). The results showed that extending the height of the porometer by 7.6 cm increased drainage and decreased water storage. When stratifying substrates, the system as a whole stores less water and has more air-filled porosity than non-stratified composite profiles (100% peatlite; 100% unprocessed bark). Assumptions regarding the static physical properties of a stratified system can be made with the standard or extended porometer core for coarse-textured bark substrates with reasonable accuracy (< 5% difference); though, assumptions cannot accurately be assessed for finer peat-based stratified profiles.

Technical Abstract: Soilless substrate stratification is increasing in popularity in the nursery and greenhouse industry globally. The concept of stratifying substrates entails stacking two substrates with different physiochemical properties to augment vertical moisture balances and redistribution. Stratified substrate research to date has estimated or assumed that the static physical properties of a stratified system as the mean of the individual strata components. No research to date has verified or rejected this assumption utilizing a stratified column. The research herein measured the static physical properties of a (1) peatlite (85% peat: 15% perlite), (2) unprocessed < 12.7 mm aged bark, (3) fine bark particles (= 6.3 mm) and (4) coarse bark particles (= 6.3 mm). Moreover, these physical properties were measured via (1) using the standard promoter analysis (7.6 cm core), (2) extending the core height by stacking two standard porometer cores (15.2 cm height) of the same strata component atop each other (to identify how water storage and air-filled porosity changes), and (3) stratifying either (i) peatlite over unprocessed bark or (ii) fine bark over coarse bark. The results showed that extending the height of the porometer increased drainage and decreased water storage. When stratifying substrates, the system as a whole stores less water and has more air-filled porosity than non-stratified composite profiles (100% peatlite; 100% unprocessed bark). Assumptions regarding the static physical properties of a stratified system can be made with the standard or extended porometer core for coarse-textured bark substrates with reasonable accuracy (< 5% difference); though, assumptions cannot accurately be assessed for finer peat-based stratified profiles.