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  • Author or Editor: James S. Owen Jr x
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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.

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A cold hardiness evaluation of 57 cultivars and species of grevillea (Grevillea) was conducted from 2011 to 2014 in Aurora, OR, to assess landscape suitability in the Pacific Northwest United States. Plants were established using irrigation in 2011, but they received no supplemental water, mineral nutrients, or pruning from 2012 to 2014. Plants were evaluated for injury in Mar. 2012 and Jan. 2014 after winter cold events with minimum temperatures of −4 and −13 °C, respectively. Damage, at least on some level, occurred on most selections following their first winter after planting in 2011. During Winter 2013, further damage to, or death of, 33 grevillea cultivars or species occurred. The grevillea that exhibited the least cold damage and the most promise for landscape use and further evaluation in the Pacific Northwest United States were ‘Poorinda Elegance’ hybrid grevillea, southern grevillea (G. australis), cultivars of juniper-leaf grevillea (G. juniperina) including Lava Cascade and Molonglo, and oval-leaf grevillea (G. miqueliana), all of which exhibited minor foliage damage.

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The amount of phosphorus (P) conventionally recommended and applied to container nursery crops commonly exceeds plant requirements, resulting in unused P leaching from containers and potentially contributing to surface water impairment. An experiment was replicated in the Middle Atlantic Coastal Plain (MACP) and Ridge and Valley ecoregions of Virginia to compare the effect of a low-P controlled-release fertilizer (CRF, 0.9% or 1.4% P depending on species) vs. a conventional CRF formulation (control, 1.7% P) on plant shoot growth, crop quality, and substrate nutrient concentrations of four species: ‘Natchez’ crape myrtle (Lagerstroemia indica × Lagerstroemia fauriei), ‘Roblec’ Encore azalea (Rhododendron hybrid), ‘Radrazz’ Knock Out rose (Rosa hybrid), and ‘Green Giant’ arborvitae (Thuja plicata × Thuja standishii). In both ecoregions, the low-P CRF resulted in 9% to 26% lower shoot dry weight in all four species compared with those given the conventional formulation, but quality ratings for two economically important species, ‘Radrazz’ Knock Out rose and ‘Green Giant’ arborvitae, were similar between treatments. When fertilized with the low-P CRF, ‘Roblec’ Encore azalea and ‘Natchez’ crape myrtle in both ecoregions, and ‘Green Giant’ arborvitae in the MACP ecoregion had ∼56% to 75% lower substrate pore-water P concentrations than those that received the control CRF. Nitrate-nitrogen (N) concentrations in substrate pore water at week 5 were more than six times greater in control-fertilized plants than in those that received a low-P CRF, which may have been a result of the greater urea-N content or the heterogeneous nature of the low-P CRFs. Lower water-extractable pore-water P and N indicate less environmental risk and potentially increased crop efficiency. Our results suggest low-P CRFs can be used to produce certain economically important ornamental nursery crops successfully without sacrificing quality; however, early adopters will need to evaluate the effect of low-P CRFs on crop quality of specific species before implementing on a large scale.

Open Access

Many research studies have evaluated potential organic and mineral container substrate components for use in commercial potting substrates. Most studies report results of plant growth over a single production season and only a few include physical properties of the substrates tested. Furthermore, substrates containing predominantly organic components decompose during crop production cycles producing changes in air and water ratios. In the commercial nursery industry, crops frequently remain in containers for longer periods than one growing season (18 to 24 months). Changes in air and water retention characteristics over extended periods can have significant effect on the health and vigor of crops held in containers for 1 year or more. Decomposition of organic components can create an overabundance of small particles that hold excessive amounts of water, thus creating limited air porosity. Mineral aggregates such as perlite, pumice, coarse sand, and calcined clays do not decompose, or breakdown slowly, when used in potting substrates. Blending aggregates with organic components can decrease changes in physical properties over time by dilution of organic components and preserving large pore spaces, thus helping to maintain structural integrity. Research is needed to evaluate changes in container substrates from initial physical properties to changes in air and water characteristics after a production cycle.

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Nursery and greenhouse growers use a variety of practices known as best management practices (BMPs) to reduce sediment, nutrient, and water losses from production beds and to improve efficiency. Although these BMPs are almost universally recommended in guidance manuals, or required by regulation in limited instances, little information is available that links specific BMPs to the scientific literature that supports their use and quantifies their effectiveness. A previous survey identified the most widely used water management, runoff, and fertilizer-related BMPs by Virginia nursery and greenhouse operators. Applicable literature was reviewed herein and assessed for factors that influence the efficacy of selected BMPs and metrics of BMP effectiveness, such as reduced water use and fertilizers to reduce sediment, nitrogen (N), and phosphorus (P) loads in runoff. BMPs investigated included vegetative zones (VZs), irrigation management strategies, and controlled-release fertilizers (CRFs). Use of vegetative buffers decreased average runoff N 41%, P 67%, and total suspended solids 91%. Nitrogen, P, and sediment removal efficacy increased with vegetative buffer width. Changes in production practices increased water application efficiency >20% and decreased leachate or runoff volume >40%, reducing average N and P loss by 28% and 14%, respectively. By linking BMPs to scientific articles and reports, individual BMPs can be validated and are thus legitimized from the perspective of growers and environmental regulators. With current and impending water use and runoff regulations, validating the use and performance of these BMPs could lead to increased adoption, helping growers to receive credit for actions that have been or will be taken, thus minimizing water use, nutrient loss, and potential pollution from nursery and greenhouse production sites.

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Nursery and greenhouse producers, research and extension faculty, and representatives from allied fields collaborated to formulate a renewed vision to address water issues affecting growers over the next 10 years. The authors maintained the original container irrigation perspective published in “Strategic vision of container nursery irrigation in the next ten years,” yet broadened the perspective to include additional challenges that face nursery crop producers today and in the future. Water availability, quality, and related issues continue to garner widespread attention. Irrigation practices remain largely unchanged due to existing irrigation system infrastructure and minimal changes in state and federal regulations. Recent concerns over urbanization and population growth, increased climate variability, and advancements in state and federal regulations, including new groundwater withdrawal limitations, have provided an inducement for growers to adopt efficient and innovative practices. Information in support of the overarching issues and projected outcomes are discussed within.

Open Access