Single-screen Bark Particle Separation Can be Used to Engineer Stratified Substrate Systems

Abstract

Substrate stratification is an emerging substrate management strategy involving layering multiple substrate materials within a single container to modify physiochemical characteristics of the substrate system. Specifically, stratifying allows growers and researchers to rearrange the air–water balance within a container to modify hydraulic characteristics. Moreover, fertilizer can be incorporated into just the upper strata to reduce leaching. Research to date has shown benefits associated with resource efficiency, production timing, and weed control. With the associated benefits for substrate stratification, interested growers will need pragmatic solutions for onsite trials. Therefore, the objective of this study was to identify a cost-effective solution for growers interested in exploring stratification options. As such, this research was designed to identify a single-screen bark separation to generate fine and coarse bark textures suitable for use as the top and bottom substrate strata. Loblolly pine bark (Pinus taeda) was screened with either a 4.0-mm, 1/4-inch, or 3/8-inch screen, with the particles passing through the screen (unders) separated from retained particles (overs). Stratified substrate systems were engineered with an individual screen wherein the fines were layered atop the coarse particles from the same screen. ‘Natchez’ crepe myrtle (Lagerstroemia indica) liners were planted in either of the three stratified substrate treatments or a nonstratified control. Substrate physical characteristics were assessed for each strata by pre- and postproduction properties to identify changes of substrate. The final growth index of the crop was unaffected by the substrate treatment (P = 0.90); however, stratified substrates did increase dry root weight (P = 0.02), with the smallest screen (4.0 mm) resulting in the greatest root weight. Separation of roots between the two strata indicated the presence of more roots in the upper strata in all substrates. However, the stratified substrates resulted in a greater shift in root location, encouraging increased rooting in the upper strata with fine particles, with the largest screen (3/8 inch) resulting in the greatest differentiation between upper and lower rooting. Each stratified treatment had increase in water-holding capacity in the lower (coarser) strata without changes in the upper strata. Thus, we conclude that single screens can be used to build stratified substrate systems. Moreover, screen aperture size may be used to achieve different outcomes with regard to root growth and development as well as water–air balance. Further research may indicate that screen selection may be used to target specific crop needs.

Stratified Substrates Can Reduce Peat Use and Improve Root Productivity in Container Crop Production

“…Thus, the greater root biomass in the lower stratum may be attributed to larger roots. These results contrast the results observed by Fields et al (2022), where there were greater root biomass values measured in the upper strata than lower. However, the system used fine bark particles layered over coarse bark; thus, there were different pore diameters and distributions (peat-based substrate vs. screened fine bark particles; unscreened bark vs. screened coarse bark).…”

“…Promising results have demonstrated that substrate stratification may support possibilities for nursery growers to reduce water and fertilizer inputs by 25% and 20%, respectively, and continue producing equivalent or better crops than traditionally used nursery production methods (Criscione et al 2022a;Fields et al 2021b). Evidence has also shown improved containerized crop rooting in stratified systems when compared with conventional growing practices (Fields et al 2022). Moreover, others have used stratified substrate concepts to stratify controlled-release-fertilizer placement (Ammons et al 2022) and to reduce weed germination and associated herbicide application costs in container systems (Khamare et al 2022).…”

The Pour-through Procedure Preferentially Extracts Substrate Solution from the Bottom of the Container in Conventional and Stratified Substrates

“…This suggests that some aspect of solute transport in the stratified container made it more conducive for mineral nutrients to migrate from the top of the container to the bottom. However, literature has shown that pourthrough extracts result in lower EC if fertilizer is placed in the top half of the container in ), dissolved inorganic nitrogen (DIN; NH traditional (Ammons et al 2022) or in a stratified substrate (Fields et al 2022). This could be because of the distance the applied water travels and displaces (if piston flow occurs) or mixes the resident solution in the substrate as illustrated herein, or because of decreased infiltration rate, preferential flow, and water velocity when stratifying substrate (Criscione et al 2022b).…”

Root Exploration, Initial Moisture Conditions, and Irrigation Scheduling Influence Hydration of Stratified and Non-Stratified Substrates

“…As measured by quality ratings and overall growth (i.e., physiological measurements), the equal or greater performance of crops produced in the stratified substrate systems have been reported [6,[9][10][11]. In the stratified systems, improved crop growth and quality were the most notable within the first year, especially during crop establishment [6].…”