Soilless substrate stratification: a review of the past and looking forward

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

Submitted to: Acta horticulturae
Publication Type: Review Article
Publication Acceptance Date: 6/19/2023
Publication Date: 2/26/2024
Citation: Fields, J.S., Owen Jr, J.S. 2024. Soilless substrate stratification: a review of the past and looking forward. Acta Horticulturae. 1389:61-66. https://doi.org/10.17660/ActaHortic.2024.1389.7.
DOI: https://doi.org/10.17660/ActaHortic.2024.1389.7

Interpretive Summary: Annual sales of specialty crops (i.e., nursery, floriculture, fruit, vegetables, medicinal, etc.) produced in soilless culture, both nationally (USDA, 2020) and internationally, continues to rapidly increase. This is primarily due to (1) the increase in human population (i.e., estimated 10 billion by 2050; (2) greater income and improved standards of living, driving the demand for high-value food, produce, and ornamental commodities, especially out-of-season, and (3) an ongoing transition to soilless substrate systems from in ground production augmenting production efficacy when compared to soil-based cultivation. Thus, soilless substrate usage and reliance is predicted to increase more than 400% in the upcoming 30 years. Soilless substrate engineering can lead towards more sustainable substrates partly by reducing overall water and fertilizer, subsequent nutrient leaching, and reliance on Sphagnum peat. Soilless substrate stratification is one such engineered practice that is garnering attention throughout specialty crop production. Soilless substrate stratification is where unique layers of substrates with differing physicochemical properties are placed atop of each other to intentionally create a distinctive physical, chemical, and hydraulic stratum in a container altering both the water and chemical gradient relative to conventional, homogenously filled containers. current research shows that substrate stratification can reduce water and fertilizer applications, reduce weed pressure, reduce peat use and reliance, and improve containerized crop root growth. More research is needed to fully understand the benefits of stratified substrates.

Technical Abstract: Containerized crop production is an intensely managed system comprise of highly porous substrates that rely upon natural resources (i.e., peat, bark, water, and mineral nutrients) to quickly provide salable crops throughout the year. The cost of these finite resources have been rising partly in response to soilless production practices expanding into new agricultural sector and supply chain matters. To alleviate rising costs and supply limitations, researchers must identify new and innovative crop-production strategies. Substrate stratification is an emerging substrate management technique that involves layering unique substrates within a container for more precise control of container-substrate air or water gradient. Results have demonstrated improved resource efficiency, allowing strategic fertilizer placement to reduce overall fertilizer requirements and improved productivity when produced under deficit water management. More recent evidence has shown improved root productivity for crops grown in stratified substrates. Most recently, peat reduction through utilization of stratified systems, peat atop bark, has been successfully employed. Thus, stratified substrates are gaining interest in both nursery and greenhouse production. As we continue to uncover the benefits of alternative media management strategies like stratified substrates, more refined research is necessary to quantify the advantages to growers, researchers, and the global public. This paper will explore the present and future of stratified substrate research, focusing on the beginning theories through current discoveries. We will discuss existing technologies and upcoming experimentation plans to advance stratified substrate science and further explore associated benefits with the goal of expanding innovative agriculture research to yield more cost-effective and environmentally friendly production strategies that are achievable through soilless substrate science.