Bark particle screening is a critical secondary processing stage when engineering bark-based horticultural substrates. There are several factors that can influence bark screening efficiency; however, the bark moisture content immediately before screening may have the largest impact. The objectives of this study were to determine the effect bark moisture content has on bark particle separation across two commonly used screen apertures and the subsequent static physical properties of the screened bark. The moisture contents examined herein ranged from 50%, 55%, 60%, 65%, and 70% and were gravimetrically determined. The screen apertures used were 6.3 mm and 9.5 mm. The results showed that moisture content has a considerable effect on both screening yield and the physical properties. Generally, as moisture content increased, bark yield (i.e., bark processed through the aperture) decreased. Moreover, as moisture content increased, the proportions of fine bark particles adhered to coarse bark increased, shifting the air-filled porosity: water-holding capacity of the substrate. In summation, the drier moisture content had the greatest (i.e., most equal) separation, regardless of screen aperture. Future research should identify the interaction between feed rate and moisture content.
Peat use in horticulture continues to be scrutinized as consumers are becoming increasingly aware of the environmental sustainability concerns associated with peat. Thus, the horticultural industry is driven to search for peat alternatives. Substrate stratification (i.e., vertical layering of unique media atop another in a singular container) has been studied in nursery substrates and has demonstrated improved resource efficiency with regard to water and fertilizer inputs. However, minimal research has evaluated using the concept of stratified substrates as an attempt to reduce peat inputs in greenhouse production. Hence, the objective of this study was to identify if stratifying costly floriculture media atop of low-cost pine bark can reduce peat use, reliance, and cost within the floriculture industry. A floriculture crop, Petunia hybrid ‘Supertunia Honey’, was grown in two distinct substrate treatments: 1) nonstratified (commercial peat-based floriculture substrate) and 2) stratified peat-based substrate layered atop aged pine bark (1:1 by volume) under two different irrigation schedules. Crop growth was evaluated, including growth indices, shoot physiological responses, and root growth measurements. Substrate hydraulic properties such as matric potential and volumetric water content were monitored over time. The results demonstrated that a petunia crop can be produced in stratified substrate systems and yield similarly sized and quality crops as traditionally grown plants. Furthermore, the stratified substrate-produced crop had improved root productivity, yet less bloom, when compared with nonstratified-grown crops.
Substrate stratification is an emerging substrate management strategy involving layering multiple substrate materials within a single container to modify physiochemical characteristics of the substrate system. Specifically, stratifying allows growers and researchers to rearrange the air–water balance within a container to modify hydraulic characteristics. Moreover, fertilizer can be incorporated into just the upper strata to reduce leaching. Research to date has shown benefits associated with resource efficiency, production timing, and weed control. With the associated benefits for substrate stratification, interested growers will need pragmatic solutions for onsite trials. Therefore, the objective of this study was to identify a cost-effective solution for growers interested in exploring stratification options. As such, this research was designed to identify a single-screen bark separation to generate fine and coarse bark textures suitable for use as the top and bottom substrate strata. Loblolly pine bark (Pinus taeda) was screened with either a 4.0-mm, 1/4-inch, or 3/8-inch screen, with the particles passing through the screen (unders) separated from retained particles (overs). Stratified substrate systems were engineered with an individual screen wherein the fines were layered atop the coarse particles from the same screen. ‘Natchez’ crepe myrtle (Lagerstroemia indica) liners were planted in either of the three stratified substrate treatments or a nonstratified control. Substrate physical characteristics were assessed for each strata by pre- and postproduction properties to identify changes of substrate. The final growth index of the crop was unaffected by the substrate treatment (P = 0.90); however, stratified substrates did increase dry root weight (P = 0.02), with the smallest screen (4.0 mm) resulting in the greatest root weight. Separation of roots between the two strata indicated the presence of more roots in the upper strata in all substrates. However, the stratified substrates resulted in a greater shift in root location, encouraging increased rooting in the upper strata with fine particles, with the largest screen (3/8 inch) resulting in the greatest differentiation between upper and lower rooting. Each stratified treatment had increase in water-holding capacity in the lower (coarser) strata without changes in the upper strata. Thus, we conclude that single screens can be used to build stratified substrate systems. Moreover, screen aperture size may be used to achieve different outcomes with regard to root growth and development as well as water–air balance. Further research may indicate that screen selection may be used to target specific crop needs.
Growers rely on soilless substrates to provide sufficient water and nutrients to containerized crops. Traditional bark-based substrates are engineered to have relatively low water-holding capabilities, which can lead to nonuniform rewetting patterns and inefficient usage of water resources. Engineering substrates to redistribute water dynamics and maximize aeration within the container may improve water resource efficiencies. The goal of this study was to evaluate whether more efficient irrigation schedules can be used when stratifying unique substrates within a container for added crop water and nutrient efficiency. Loropetalum chinense ‘Ruby’ liners were planted and grown in a conventional pine bark substrate or one of three stratified substrate treatments, including a bark:peat, bark:coir, or fine bark layered on top of a coarse bark. The crops were grown under four different irrigation schedules, including single daily application, single application at deficit levels, cyclic application, or cyclic at deficit schedules. Stratified substrates improved crop growth, quality, and yield when compared with plants grown in conventional bark in the single application irrigation treatment. Measured at final harvest, substrates positively influenced plant growth index (P < 0.0001), whereas irrigation scheduling alone had no effect (P = 0.6321). There was a strong interaction between substrate and irrigation schedules on Δ growth index (P = 0.0141). There were strong substrate effects on shoot dry weight (P = 0.0060), root dry weight (P = 0.0342), and growth index (P = 0.0040). The stratified bark:coir treatment outgrew all other substrate treatments. In addition, within all irrigation treatments, plants grown with the stratified bark:coir substrate had the highest survival ratings among the other substrate treatments, whereas the conventional bark had the lowest survival rates. Substrate and irrigation had an effect on nitrogen and potassium leachate concentrations levels (P = 0.0107 and P = 0.0004, respectively). Evaluation of microbial communities showed that substrate (P = 0.0010) and the stratified layer (P = 0.0010) had strong influences on the type of community present and the relative abundance in the treatments used herein this study. Specifically, within cyclic scheduling, bark:peat actinomycete populations were significantly greater than other substrate treatments. Furthermore, under deficit irrigation, stratified substrate systems were able to mitigate crop water stress. The results indicate that when crops such as the Loropetalum are grown in the stratified system, crop growth can be sustained when drought conditions are present. This is possible by providing adequate water availability even under low water inputs until subsequent irrigations during the fragile establishment period, when compared with using traditional bark-based substrates.