A study was conducted to quantify the effect of substrate texture on water-holding capacity of douglas fir [Pseudotsuga menziesii (Mirb.) Franco] bark (DFB) in containers of varying height. Medium (less than 2.2 cm) and fine (less than 0.9 cm) DFB were packed into 7.6 cm i.d. aluminum cores 3.8, 7.6, and 15.2 cm tall to determine container capacity (CC) and air space (AS) at varying container heights. Increasing container height resulted in a linear decrease in CC and a linear increase in AS. Fine texture DFB bulk density (Db) increased 18% with increasing container height, whereas Db of medium texture DFB was unaffected. Water-holding capacity decreased 20% and 42% in medium and fine textured DFB, respectively, with increasing container height from 3.8 to 15.2 cm. A second study was conducted to investigate water distribution in a 15.2-cm tall container for a given substrate texture. Polyvinyl chloride cores (15.2 cm tall × 7.6 cm i.d.) were packed with the same substrates, drained to CC, frozen, and sawed into 2.5-cm sections to determine water-holding capacity at each height. A finer substrate texture increased the amount of water throughout the container profile, but percent of total water for each strata remained similar. Container height and plant size (i.e., transplant or salable), in relation to substrate texture, should be considerations when producing containerized crops. In addition, bark texture alters water-holding capacity and water distribution within the container, ultimately affecting water management practices.
Douglas fir [Pseudotsuga menziesii Mirb. (Franco)] bark (DFB), sphagnum peatmoss, and pumice are the most common substrate components used in the Oregon nursery industry. The objective of this study was to document the effect of peat and pumice addition on the physical and hydrological properties of DFB soilless substrates. A secondary objective was to determine if measured properties of mixed soilless substrates can be accurately predicted from the known properties of the individual components. Treatment design was a 3 × 3 factorial with three rates each of sphagnum peatmoss and pumice (0%, 15%, and 30% by vol.) added to DFB. The resulting nine substrates were measured for total porosity, air space, container capacity, and bulk density using porometers. Moisture characteristic curves were generated by measuring water content along a continuous column. Adding pumice to DFB decreased total porosity, container capacity, available water, and water-buffering capacity but increased bulk density. Adding peatmoss to DFB increased total porosity, container capacity, and available water but decreased air space and bulk density. Comparison of predicted values against measured values indicated that bulk density could be predicted reliably; however, all other physical properties could not be accurately predicted.
In the future, the U.S. ornamental horticulture industry may be faced with limited water resources and increased requirements to reduce pollution runoff from production areas. The concerns are most evident to outdoor, uncovered container crop production, which relies on daily irrigation. Capture of precipitation and irrigation runoff from ornamental horticulture nurseries to be recycled as irrigation could potentially generate cost savings relative to the cost of alternative water sources. Existing nurseries may incur large investment costs to modify their infrastructure for water capture to recycle. These added costs must be compared with costs of alternative sources such as off-farm municipal or on-farm well water. Using both existing case nurseries and simulated nurseries, this study employed partial budgeting for comparison of annual costs of recapture and recycling to the alternatives of either municipally delivered water or on-farm well extraction. On-site visits were conducted at mid-Atlantic ornamental horticulture operations that recycle water currently to gather data for constructing budgets and to determine factors that enhance or inhibit nursery adoption of recycling. The partial budgeting analysis was followed by breakeven analysis with regard to costs of regrading, pond excavation, and opportunity costs of land to isolate their effects on the nursery adoption decision. Six of eight case nurseries currently obtaining from 20% to 100% of their irrigation needs from recycled water achieve lower production costs as a result of recycling compared with using alternative municipal or well water sources. Recycling would also reduce pollution runoff as water containing nutrients and chemicals would be retained for reuse on the farm rather than being discharged to public water bodies. Two case nurseries and two simulated nurseries that were constructed based on average conditions for nurseries participating in a mail survey see higher production costs as a result of recycling. The cost of land regrading for water recapture, excavating the recapture pond, and the opportunity cost of production area occupied by the recapture pond are critical for determination of the least cost outcome. Public funding incentives for water collection and recycling could motivate increased water conservation and reduced pollution runoff within the horticulture industry.
Moisture characteristic curves (MCC) relate the water content in a substrate to the matric potential at a given tension or height. These curves are useful for comparing the water-holding characteristics of two or more soils or soilless substrates. Most techniques for developing MCC are not well suited for measuring low tensions (0 to 100 cm H2O) in coarse substrates used in container nursery production such as those composed of bark. The objectives of this research were to compare an inexpensive modified long column method with an established method for creating low-tension MCCs and then to determine the best model for describing MCCs of bark-based soilless substrates. Three substrates composed of douglas fir (Pseudotsuga menziesii) bark alone or mixed with either peatmoss or pumice were used to compare models. Both methods described differences among the three substrates, although MCC for each method differed within a substrate type. A four-parameter log-logistic function was determined to be the simplest and most explanatory model for describing MCC of bark-based substrates.
An experiment was conducted to test the hypothesis that either pumice or plant roots maintain air space (AS) and porosity over time, or renders substrates more resistant to shrinkage. Treatment design was a 3 × 2 factorial with three substrate types and either presence or absence of a plant. The three substrates were composed of douglas fir (Pseudotsuga menziesii) bark alone or amended with 15% or 30% (by volume) pumice. Substrates were packed in aluminum cores to facilitate measurement of physical properties with porometers at the conclusion of the experiment. Half of the cores with each of the three substrate types were packed with a single plug of ‘Autumn Blush’ coreopsis (Coreopsis sp.) (Expt. 1) or ‘Blue Prince’ holly (Ilex ×meserveae) (Expt. 2). The remaining cores were maintained in the same production environment, but without a plant. Substrate physical properties were measured before the experiment and after 48 days for coreopsis plants and 382 days for holly. Both experiments had relatively similar responses despite using different crops and production times. Summarizing in general overall treatments, AS decreased, container capacity (CC) and total porosity (TP) increased, and bulk density remained constant over time. The presence of a plant in the core tended to exacerbate the decrease in AS and the increase in core capacity. Shrinkage was decreased by the presence of a plant, but only minimally.
Many soilless substrates are inefficient with regard to water (i.e., high porosity and low water holding capacity), which provides an excellent opportunity to increase water efficiency in containerized production. We suggest that increasing hydraulic conductivity in the dry range of substrate moisture content occurring during production can increase water availability, reduce irrigation volume, and produce high quality, marketable crops. Three substrates were engineered using screened pine bark (PB) and amending with either Sphagnum peatmoss or coir to have higher unsaturated hydraulic conductivity between water potentials of −100 and −300 hPa. There was no correlation between substrate unsaturated hydraulic conductivity and saturated hydraulic conductivity (r = 0.04, P = 0.8985). Established Hydrangea arborescens (L.) ‘Annabelle’ plants were grown in the three engineered and a conventional (control) PB substrates exposed to suboptimal irrigation levels (i.e., held at substrate water potentials between −100 and −300 hPa) for 32 days. The plants in the engineered substrates outperformed the control in every growth and morphological metric measured, as well as exhibiting fewer (or no) physiological drought stress indicators (i.e., vigor, growth, plant development, etc.) compared with the control. We observed increased vigor measures in plants grown in substrates with higher unsaturated hydraulic conductivity, as well as greater plant water uptake. The coir increased unsaturated hydraulic conductivity and provided an increased air space when incorporated into coarse bark vs. if peat was incorporated into bark at the same ratio by volume. Increasing PB hydraulic conductivity, through screening bark or amending bark with fibrous materials, in concert with low irrigations can produce marketable, vigorous crops while reducing water consumed and minimizing water wasted in ornamental container production.
Regulatory and economic incentives to improve water and fertilizer use efficiency have prompted the nursery industry to seek new and advanced techniques for managing the production of ornamental crops. The development of best management practices, especially with regard to fertilizer and irrigation management, is largely based on research that looks at season-long trends in water and nutrient use. Understanding how water moves through a substrate during a single irrigation event may allow for the refinement of recommended best management practices that improve water and fertilizer use efficiency in container-grown plant production systems. Therefore, a study was conducted to characterize the movement of irrigation water at three growth stages [4, 9, and 17 weeks after transplanting (WAT)] throughout the production cycle of Ilex crenata Thunb. ‘Bennett’s Compactum’ that were container-grown in a bark-based substrate alongside fallow (i.e., without a plant) containers. Tensiometers were placed at three horizontal insertion depths and three vertical heights throughout the substrate profile to detect changes in matric potential (ψ; kPa), during individual irrigations. At 4 WAT, the pre-irrigation ψ in the upper substrate profile was 12.3 times more negative (i.e., drier) than the substrate near the container’s base and 6.0 times more negative than the middle of the container. This gradient was decreased at 9 and 17 WAT as roots grew into the lower portion of the substrate profile. On average, water began to drain from the base of containers 59.9 s ± 1.0 se and 35.7 s ± 1.3 se after irrigation commencement for fallow containers and plant-containing treatments, respectively, indicating channeling through the substrate of plant-containing treatments. A pattern of plant water uptake by roots induced a gradient in the substrate’s pre-irrigation moisture distribution, where portions of the substrate profile were relatively dry where plant roots had taken up water. Consequently, the application of water or fertilizer (i.e., fertigation) through irrigation has the potential to be highly inefficient if applied under dry substrate conditions where channeling may occur. Therefore, water application using cyclic irrigation or substrate moisture content (MC) thresholds (not letting MC fall below an undetermined threshold where channeling may occur) may improve water application efficiency. Furthermore, fertigation should occur when the substrate MC in the upper portion of the container is higher than the pre-irrigation MCs observed in this study to minimize the occurrence of channeling. The effect of root growth should also be taken into account when seeking the proper balance between pre-irrigation substrate MC and irrigation application rate to reduce the risk of unwanted channeling.
Maximizing nutrient use efficiency while minimizing nutrient leaching and non-point source contributions from containerized crop production systems are goals of researchers and growers. These goals have led to irrigation and crop nutrition management practices that reduce fertilizer and irrigation expenditures and reduce the nutrient load into the environment. However, one area that has received little attention, and may lead to the further refinement of crop management practices, is how dissolved nutrients (solutes) move through a substrate while water is being applied during irrigation. A study was conducted to characterize the effect of a controlled-release fertilizer (CRF) placement method on changes in leachate nutrient concentration throughout an irrigation event and to evaluate these changes at different times throughout a production season. A pine bark:sand (9:1, by volume) substrate was placed in 2.7-L nursery containers (fallow) and was treated with topdressed, incorporated, and dibbled CRF or did not receive CRF. The nutrient leaching pattern was evaluated at 3, 9, and 15 weeks after potting (WAP). Leachate nutrient concentration was the highest in the first 50 mL of effluent and steadily diminished as irrigation continued for the topdressed, incorporated, and the no CRF treatments. Effluent nutrient concentration from containers with dibbled CRF generally increased throughout the first 150 mL of effluent, plateaued briefly, and then diminished. The nutrient load that leached with higher volumes of irrigation water was similar between incorporated and dibbled CRF placements. However, the unique nutrient leaching pattern observed with the dibbled CRF placement method allowed for a lower effluent nutrient load when leaching fractions are low. Dibble may be an advantageous CRF placement method that allows for the conservation of expensive fertilizer resources and mitigates non-point source nutrient contributions by reducing undesired nutrient leaching during irrigation.
Phosphorus (P) uptake efficiency (PUE; percent of applied P absorbed by roots) for containerized crops is ≈27% to 62%. Reducing P fertilization may increase PUE without decreasing growth and may reduce P leaching from containers, thus mitigating the environmental impact of containerized production while potentially reducing fertilizer input costs for growers. The objective of this study was to determine the minimum P application concentration and the resulting substrate pore-water (i.e., solution residing within and between substrate particles) P concentration that maintains maximal growth of three containerized woody plant taxa grown in pine bark substrate. Hydrangea paniculata Sieb. ‘Limelight’ (hydrangea), Ilex crenata Thunb. ‘Helleri’ (holly), and Rhododendron L. ‘Karen’ (azalea) were potted in pine bark substrate amended with dolomite and micronutrients and grown for 81 d in an open-wall greenhouse. Plants received either one of five constant liquid-feed treatments with varying P concentrations [80 mg·L−1 nitrogen (N), 50 mg·L−1 potassium (K), and 0.5, 1.0, 2.0, 4.0, or 6.0 mg·L−1 P] or a single application of controlled-release fertilizer (CRF; control) at experiment initiation. Calculated lowest P fertilizer concentration that sustained maximal shoot dry weight (SDW) in hydrangea and azalea was 4.7 and 2.9 mg·L−1, respectively, and holly SDW was the same across all liquid fertilizer treatments. In all three taxa, CRF-fertilized plants achieved <50% of maximal SDW observed in liquid-fertilized plants. Hydrangea root dry weight (RDW) nearly doubled as fertilizer P increased from 0.5 to 2.0 mg·L−1 P, but higher P concentrations did not further increase RDW. Holly RDW was unaffected by liquid P treatment. Pore-water P concentrations of treatments that sustained maximal SDW of hydrangea and azalea were as low as 0.6 and 2.2 mg·L−1 P, respectively. Our findings suggest that when using constant liquid feed, applied P levels more accurately predict plant growth responses than pore-water P levels.
Pine bark is the primary constituent of nursery container media (i.e., soilless substrate) in the eastern United States. Pine bark physical and hydraulic properties vary depending on the supplier due to source (e.g., lumber mill type) or methods of additional processing or aging. Pine bark can be processed via hammer milling or grinding before or after being aged from ≤1 month (fresh) to ≥6 month (aged). Additionally, bark is commonly amended with sand to alter physical properties and increase bulk density (Db). Information is limited on physical or hydraulic differences of bark between varying sources or the effect of sand amendments. Pine bark physical and hydraulic properties from six commercial sources were compared as a function of age and amendment with sand. Aging bark, alone, had little effect on total porosity (TP), which remained at ≈80.5% (by volume). However, aging pine bark from ≤1 to ≥6 months shifted particle size from the coarse (>2 mm) to fine fraction (<0.5 mm), which increased container capacity (CC) 21.4% and decreased air space (AS) by 17.2% (by volume) regardless of source. The addition of sand to the substrate had a similar effect on particle size distribution to that of aging, increasing CC and Db while decreasing AS. Total porosity decreased with the addition of sand. The magnitude of change in TP, AS, CC, and Db from a nonamended pine bark substrate was greater with fine vs. coarse sand and varied by bark source. When comparing hydrological properties across three pine bark sources, readily available water content was unaffected; however, moisture characteristic curves (MCC) differed due to particle size distribution affecting the residual water content and subsequent shift from gravitational to either capillary or hygroscopic water. Similarly, hydraulic conductivity (i.e., ability to transfer water within the container) decreased with increasing particle size.