S06 - Session O6 - Substrate stratification can be paired with strategic irrigation practices to improve container-water dynamics.

Authors: Kristopher Criscione, Jeb Fields *, James Owen

The increase in horticultural production and the subsequent intensification of horticultural water use justifies a need to engineer growing media for increased resource efficiency. Substrate stratification is a possible solution to augmenting nursery resource management. This practice involves the redistribution of the air:water balance within the container profile by means of stacking or layering unique media components within the container. The objective of this research was to evaluatethe water balance of a stratified substrate system vs. a traditional pine bark growing media . In this study, stratified substrate systems were developed by layering fine pine bark particles ( < 6.3 mm) atop coarse pine bark particles ( > 6.3 mm). This system was then evaluated against an unscreened pine bark control. Moisture retention curves were assessed for the three bark materials utilized (unscreened, coarse, and fine), and a HYDRUS-1D model representing hydraulic equilibrium was developed for the two soilless substrate systems. A floriculture crop ( Dianthus barbatus interspecific 'PAS970056') was grown in both unscreened pine bark and stratified pine bark under single and cyclic irrigation cycles. Tensiometers were installed in the upper and lower proportion of the containers (both stratified and control) and a volumetric water content sensor was placed in the center of the container. Moisture status was monitored hourly. The moisture retention curves identify that conventional bark has a more heterogeneous pore size distribution than fine and coarse bark particles. The HYDRUS model indicates nearly a 50% reduction in moisture gradient profile from the top surface to the bottom of the container in stratified substrate systems. Moreover, stratified substrates reduced the tension fluctuations that occur in the upper portion of the substrate profile during a single irrigation application when compared to non-stratified systems. When stratified substrates were paired with cyclic irrigation, the hydraulic uniformity was further increased. When a single irrigation application was applied, stratified substrates exhibited increased drainage. In contrast, when more frequent, reduced volume irrigations were applied, stratified substrates were more efficient at water retention than non-stratified systems. In all, substrate stratification has the potential to reduce overall water use while simultaneously decreasing the energy required for plants roots to uptake water and nutrients.