Stratified substrates enhance water storage and distribution between irrigation events

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

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2023
Publication Date: 2/23/2024
Citation: Criscione, K.S., Fields, J.S., Owen Jr, J.S., Gentimis, A. 2024. Stratified substrates enhance water storage and distribution between irrigation events. Soil Science Society of America Journal. 88(2): 387-402. https://doi.org/10.1002/saj2.20636.
DOI: https://doi.org/10.1002/saj2.20636

Interpretive Summary: Today, pine bark-based substrates are amongst the most utilized soilless substrate across 2114 ha in eastern U.S. nurseries selling $4.5 billion in crops annually in 2019. Though this enables containerized crop production to scale across manufacturing a multitude of crops, the high porosity and subsequent limited water holding capacity coupled with a non-uniform moisture content depth profile often prompts continuous (i.e., daily or hourly) reapplications of irrigation to prevent under watering crops. As a result, application volumes of 177 m3·ha-1·d-1 of irrigation can be applied during peak production season. Thus, revealing the inefficiencies pine bark substrates have with regards to water storage and use. Stratified substrate, layering different texture substrate within the same container, have presented numerous opportunities to improve production sustainability through weed suppression and decreased herbicide use/cost, explore fertilizer placement strategies, reduce fertilizer inputs by 20%, and lessen irrigation use by 25%. The fundamental objective of this study was to determine how substrate water dynamics are influenced by the stratified system between alternative irrigation scheduling methods. Thus, the hydraulic properties of individual substrate components were continually measured and modeled for water potential in the top and bottom portion of the container and water content throughout the container when irrigated once a day as single application or three times a day (i.e., cyclic application) when growing Dianthus barbatus ‘Amazon Neon Purple’ floriculture crop. Stratified containers held less water when a single irrigation schedule was implemented due to the improved drainage in 50% of the container profile. Stratified substrates retained more water when cyclical irrigation scheduling was applied because of the increased retention in the top layer. The overarching results of this manuscript exemplify that stratified substrate systems have more uniform moisture content profile distributions while potentially providing less stressful root environments for crop growth and development.

Technical Abstract: A focal point in specialty crop container production is the substrate utilized. The industry requires copious amounts of fresh or recycled water to meet production needs; however, current substrates are highly porous to mitigate risks and are subsequently inefficient with regards to water use. Therefore, more sustainable soilless substrates are needed to ensure future success and profitability of the horticultural industry, especially as finite fresh water sources become limiting. Substrate stratification (i.e., vertically layering unique substrates atop one another) provides an opportunity to augment an existing system with little change to overall production methodology. The mechanism of stratified substrates is to maintain substrate porosity, while strategically redistributing the air and water within the container system to retain more water when applied and control vertical water distribution. The aim of this research was to further understand the complex stratified systems hydraulics. Herein, the hydraulic properties of individual substrate components were measured and modeled via HYDRUS 1-D. Furthermore, matric tensions (via elbow tensiometers installed in the top and bottom layers of each substrate profiles) and volumetric water content (via moisture sensors installed in the profile center) were measured continuously under two different irrigation schedules [single application (1x) and cyclic application (3x)] for 15-d with a fully established Dianthus barbatus ‘Amazon Neon Purple’ crop. The results showed that screened bark particles have more pore homogeneity. Moreover, HYDRUS 1-D modeling demonstrated that stratified substrates have a more uniform hydraulic gradient (21%) present in the container profile when compared to non-stratified systems (45%). Regardless of irrigation schedule, stratified substrates had higher matric potential values (less negative) than non-stratified systems in both the top and bottom layer (p < 0.0001). Non-stratified upper layers experienced greater diurnal tension fluctuations under a single irrigation than in cyclic applications. Stratifying substrates resulted in a significant reduction in these fluctuations in the top layer when compared to non-stratified systems. Additionally, when both substrate (stratifying) and irrigation (cyclic) irrigation management strategies are implemented, tension fluctuations can be even further reduced and hydraulic gradients become more uniform.