Substrate Stratification: Layering Unique Substrates within a Container Increases Resource Efficiency without Impacting Growth of Shrub Rose

Abstract

Nurseries rely on soilless substrates to provide suitable growing media for container grown crops. These soilless substrates have been developed to readily drain water to prevent issues with waterlogging and associated soil-borne disease. A negative consequence of high porosity and subsequent drainage throughout the container profile is the required high or frequent irrigation rates with poor retention of applied nutrients. Substrates with relatively high levels of moisture and nutrient retention placed on top of a coarse and freely draining substrate could further optimize water and nutrient retention, while allowing for needed gas exchange for plant establishment and growth. Containerized Red Drift® rose (Rosa ‘Meigalpio’ PP17877) plants were grown under 16 mm or 12 mm daily irrigation, utilizing a traditional pine bark substrate or stratified substrates with either a conventional bark, bark fines, or a bark–peat mixture on top of a coarse bark within a container. The stratified substrates received 20% less controlled-release fertilizer; however, the fertilizer in the stratified treatments was concentrated in the upper strata only. During the first growing phase or season, plants grown in stratified substrates outperformed those grown in conventional, non-stratified bark substrates under normal irrigation. The stratified substrates did not reduce growth under reduced irrigation regimes. Overall, crop growth was equal or superior for stratified substrates when compared to the non-stratified controls, even with a 20% reduction of fertilizer. This research suggests that stratified substrate systems can be used to reduce fertilizer and irrigation rates while producing crops of similar or superior quality to conventionally grown containerized crops.

Effect of Substrate Stratification on Growth of Common Nursery Weed Species and Container-grown Ornamental Species

“…The 0.75-inch N/F bark was also constructed specifically to hold less moisture than the other substrates to evaluate its weed suppressive effect. Previous authors have also observed and noted that particle size, the only variable altered in this study, often affects the CC and AS ratios but has little effect on TP (Altland et al, 2011;Fields et al, 2021). Overall, the substrate physical property analysis indicated that although all substrates did not differ significantly, the top layers using larger particle sizes did have lower CC and greater AS compared with the 0.38inch substrate used as the bottom layer.…”

“…Substrate stratification, or layering substrates, is a new area of research and is a form of substrate engineering whereby different substrates, or different textures of the same substrate, are used within a single container (Fields et al, 2021). The current industry practice is to fill the entire container with the same substrate, resulting in the bottom portion of the container retaining more water than the top portion, requiring a higher irrigation amount or more frequent watering to provide sufficient moisture for crop plants during establishment (Fields et al, 2020(Fields et al, , 2021Owen and Altland, 2008).…”

“…Substrate stratification, or layering substrates, is a new area of research and is a form of substrate engineering whereby different substrates, or different textures of the same substrate, are used within a single container (Fields et al, 2021). The current industry practice is to fill the entire container with the same substrate, resulting in the bottom portion of the container retaining more water than the top portion, requiring a higher irrigation amount or more frequent watering to provide sufficient moisture for crop plants during establishment (Fields et al, 2020(Fields et al, , 2021Owen and Altland, 2008). Substrate physical properties such as air space (AS) and water-holding capacity are correlated with substrate particle size, with increasing water-holding capacity and decreasing AS as particle size decreases, directly impacting moisture levels within the container (Gruda and Schnitzler, 2004;Puustjarvi and Robertson, 1975;Richards et al, 1986).…”

“…Substrate physical properties such as air space (AS) and water-holding capacity are correlated with substrate particle size, with increasing water-holding capacity and decreasing AS as particle size decreases, directly impacting moisture levels within the container (Gruda and Schnitzler, 2004;Puustjarvi and Robertson, 1975;Richards et al, 1986). Fields et al (2021) showed that by placing substrates with a high level of moisture and nutrient retention capacity on top of a coarse, freely draining substrate, fertilizer rates could be reduced by 20%, with no negative effects on the growth or quality of 'Megalpio' (Red Drift V R ) roses (Rosa) compared with an industry standard substrate.…”

“…Although stratified substrates have been shown to result in improvements in terms of reduced fertilizer or more efficient utilization of irrigation, stratification described by Fields et al (2021) could be applied inversely to provide a weed control benefit. Use of larger particles forming a freely draining substrate as the top strata containing no fertilizer and a fine-textured, highly moistureretentive substrate as the bottom, stratification could combine two of the most effective nonchemical weed management techniques: strategic fertilizer placement and a mulch-like layer that holds less moisture where weed seeds will be introduced.…”