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Ronald F. Walden and Alex X. Niemiera

Container nurseries often irrigate daily with a fixed amount of water that exceeds the water-holding capacity of the container substrate, thus, leaching a portion of the applied water and nutrients. We compared the influence of daily container irrigation based on substrate moisture tension (SMT) to that of daily irrigation with a set amount on irrigation volume, container effluent volume, total effluent N content, and plant growth. Rhododendron, Ilex, and Juniperus were grown outdoors in 11.3-L containers in a pine bark-based substrate at four rates of fertilization with a controlled-release fertilizer. Drip irrigation was applied each morning until an electronic tensiometer signaled an irrigation controller that SMT was less than a set value corresponding to container capacity. Irrigation at 1.5 cm·d–1 served as the control. Irrigation treatment had little influence on growth and no influence on growth response to fertilizer rate. Irrigation volume, effluent volume, and total effluent N content were lower for each species when irrigation was based on SMT. For Juniperus, irrigation volume, effluent volume, and total effluent N content were 62%, 69%, and 60% less, respectively, for tension-based irrigation than for irrigation with a set amount.

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Ronald F. Walden and Alex X. Niemiera

The pour-through (PT) nutrient extraction method involves collection of leachate at the container bottom that results from displacement of substrate solution by water applied to the substrate surface. The PT is a convenient and effective means of monitoring the nutritional status of the soilless container substrates used in the nursery industry, but is less convenient for large containers, particularly those used in the “pot-in-pot” system of growing trees in production containers within in-ground socket containers. We describe a simple vacuum method of extracting solution from pine bark in containers using ceramic cup samplers. When N was applied to a pine bark substrate at 56–280 mg/L, extractable N was slightly higher for the PT than for the ceramic cup method. The correlation between applied and extractable N was 0.99 for both methods. Further comparison of pine bark extract nutrient and pH levels for PT and ceramic cup methods will be presented.

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Alex X. Niemiera and Carol E. Leda

A survey to determine teaching methodologies for plant material courses was conducted. A total of 120 surveys was sent to horticulture programs at U.S. universities and colleges. Thirty-nine, 22, and 8 respondents taught a woody plant (W), a herbaceous perennial (HP)/annual (A) course, and a foliage plant course, respectively; 21 respondents taught a combination of theses courses. The following similarities were noted for W and HP/A: 1) about 190 species per Semester were presented usually in a taxonomic order using slides as the primary teaching medium for lecture, 2) the most common student complaint was too much work and memorization, 3) the most common student compliment was the practical and useful nature of the subject matter, 4) in order of importance, plant identification, landscape value, and plant cultural aspects were emphasized. For W and HP/A, 93% and 65% of plants, respectively, were presented as landscape and arboreta specimens. Seventy percent of W courses used Dirr's Manual of Woody Landscape Plants; 58% and 10% of HP/A courses used Still's Manual of Herbaceous Ornamental Plants and Taylor's Guides, respectively.

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William F. Lamack and Alex X. Niemiera

Studies were conducted to evaluate the effect of water application medium moisture deficit, water application rate, and intermittent application on water application efficiency {[(amount applied - amount leached)/amount applied] x 100} of spray stake-irrigated, container-grown plants. Pine bark-filled containers were irrigated to replace moisture deficits of 600, 1200, or 1800 ml; deficits were returned in single, continuous applications of 148, 220, or 270 ml·min-l. Efficiency was unaffected by application rate but decreased with increased medium moisture deficit. In the second experiment, container medium at a 600-ml deficit was irrigated with 400 or 600 ml (6570 and 100% water replacement, respectively); deficits were returned in a single, continuous application or in intermittent 100-ml applications with 30-min intervals between irrigations. Application efficiency was greater with intermittent irrigation (95% and 84% for 400- and 600-ml replacement, respectively) than with continuous irrigation (84% and 67% for 400- and 600-ml replacement, respectively). In the third experiment, pine bark was irrigated with 600 ml water (100% replacement) in 50-, 100-, or 150-ml aliquots with 20, 40, or 60 min between applications in a factorial design. Efficiency increased with decreasing application volume and increasing time between applications. Highest efficiency (86%) was achieved with an irrigation regimen of 50-ml applications with at least 40 min between applications, compared to 62% for the control treatment (a single, continuous application of 600 ml). Our results suggest that growers using spray stakes would waste less water by applying water intermittently rather than continuously.

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William R. Feldman and Alex X. Niemiera

Determination of water needed for good function of established groundcovers in the Southwest is important in creating well-adapted, sustainable urban landscapes in this semi-arid region. Myoporum parvifolium from Australia and Dalea greggi from the Chihuahua Desert were tested at 100%, 75%, 50% and 25% of evaporation from an adjacent class A pan. Myoporum grew most at the higher irrigation regimes, but actually performed best at the lowest irrigation level, growing less than those given more water, but showing better color and vigor. Infrared leaf temperature data showed that lowest irrigation regime plants still transpired actively and had cool leaves. With Dalea, growth was directly related to water applied, with the most growth at the 100% treatment. All plants survived, but the lowest irrigation regime plants were sparse and showed definite signs of water stress. Infrared temperature measurements indicated increasing water stress as water applied decreased. At treatment onset, the Dalea had not completely covered the soil surface, so 75% of pan evaporation can be considered adequate for establishment of Dalea.

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Tyler C. Hoskins, James S. Owen Jr. and Alex X. Niemiera

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.

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Rachel Mack, James S. Owen, Alex X. Niemiera and Joyce Latimer

A survey, focusing on the use of irrigation and fertilization best management practices (BMPs), was designed and released to Virginia nursery and greenhouse growers. The objectives of the survey were to determine the most widely used BMPs, assess the reasons for their use, and identify barriers to BMP adoption. The survey was distributed in person, via e-mail attachment, or link to 357 Virginia growers in 2016 with 60 respondents. Survey results demonstrate that the most widely used BMPs in Virginia included irrigation scheduling, integrated pest management (IPM) implementation, altering irrigation practices to optimize irrigation efficiency, controlled-release fertilizer (CRF) use, and plant need–based watering. Respondents selected environmental/resource savings as one of the most cited reasons behind BMP use for water, fertilizer, and runoff management. Cost was the most cited barrier to BMP adoption for all BMPs. Fertilizer management BMP implementation was primarily an economic decision. The value of determining the most widely used BMPs and impediments to BMP adoption is that we can 1) communicate this information to growers who currently do not employ BMPs to encourage BMP adoption and 2) subsequently inform the regulatory community of BMP use. Increased BMP use can boost the potential for mitigation of agricultural nutrient and sediment runoff into impaired waterways, including the Chesapeake Bay, and help growers increase efficiency of operation inputs, such as water and fertilizer resources, while potentially saving money.

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Tyler C. Hoskins, James S. Owen Jr. and Alex X. Niemiera

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.

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Jacob H. Shreckhise, James S. Owen Jr. and Alex X. Niemiera

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.