Substrate stratification can be paired with strategic irrigation and improve container-water dynamics

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

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2023
Publication Date: 10/25/2023
Citation: Criscione, K.S., Fields, J.S., Owen Jr, J.S. 2023. Substrate stratification can be paired with strategic irrigation and improve container-water dynamics. Acta Horticulturae. 1377:553-558. https://doi.org/10.17660/ActaHortic.2023.1377.68.
DOI: https://doi.org/10.17660/ActaHortic.2023.1377.68

Interpretive Summary: The success of plant nursery production heavily relies on sustainable and efficient uses of natural resources. Specifically, the growing media in which plants are grown can have direct impacts on crop yield and subsequent resource application frequencies, such as water and fertilizer. The nursery industry is growing rapidly, where in the last decade there was an $3 billion increase in annual sales. This increase in production, in addition to the challenges agriculture faces with water availability and quality, warrants new management strategies to be developed to conserve water resources. The objective of this study was to evaluate how different irrigation schedules will influence the substrate moisture status in root explored substrate systems (a conventional homogenous profile versus stratified or layered profile). Additionally, the authors further sought to identify differences in individual strata hydraulics and validate the moisture gradient that occurs in substrate profiles through HYDRUS-1D modeling. The integration of the two moisture status parameters and techniques employed herein can allow for an overarching understanding of the water dynamics that occur in substrate systems. The result herein demonstrates that screening pine bark particles can have significant effects in manipulating the air space to water holding capacity ratio. Traditional bark-based substrates have intermediate static physical properties of that of screened bark particles. Layering fine bark particles atop coarse bark can produce a dynamic substrate profile with regards to water movement and distribution. Stratified profiles have a more uniform moisture content profile distribution (approx. 21%), whereas conventional profiles have >2x of that of stratified systems (approx. 45%). A single irrigation resulted in traditional substrates experiencing lower plant available water than in stratified systems. However, increasing irrigation frequency improved water availability regardless of substrate, but stratified to a higher degree. In all, when both substrate (stratified) and irrigation (cyclic or frequent) management practices were employed, there is a more uniform moisture content profile.

Technical Abstract: 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 evaluate the 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.