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  • Author or Editor: James Altland x
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Dolomitic lime (DL) is the primary liming agent used for increasing pH in peatmoss-based substrates. Steel slag (SS) is a byproduct of the steel manufacturing industry that has been used to elevate field soil pH. The objective of this research was to determine the pH response of a peatmoss-based greenhouse substrate to varying rates of DL or SS. Two experiments were conducted with an 85 peatmoss : 15 perlite substrate. In the first experiment, the substrate was amended with 0, 2.4, 4.8, or 7.1 kg·m−3 of either DL or SS. Half of the containers remained fallow and the other half were potted with a single sunflower (Helianthus annuus L. ‘Pacino Gold’). In the second experiment, fallow containers were only used with the substrate amended with 0, 2.4, 4.8, 9.5, or 14.2 kg·m−3 DL or SS. Sunflower were measured for relative foliar chlorophyll content, shoot mass, root ratings, and foliar nutrient concentrations. Substrate electrical conductivity (EC) and pH were measured weekly using the pour-through procedure. All sunflower plants grew vigorously, although nonamended controls had less shoot dry weight than those amended with DL or SS. There were minor differences in foliar concentration of N, Ca, Mg, and Mn; however, these differences did not adversely affect plant growth. Summarizing across both experiments, EC was affected by treatment and time, although all substrates had EC readings within the range recommended for floriculture crop production (1.0–4.6 mS⋅cm−1). Substrate pH differed slightly in Expt. 1 between fallow and planted containers. Substrate pH increased exponentially with increasing rates of either DL or SS. Maximum pH in fallow DL and SS amended substrates was 6.57 and 6.93, respectively, in Expt. 1 and 6.85 and 7.67, respectively, in Expt. 2. The SS used in this experiment resulted in a greater pH response than DL with higher application rates. SS is a viable material for raising pH of soilless substrates.

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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.

Open Access

Container-grown nursery crops generally require daily irrigation applications and potentially more frequent applications during the hottest part of the growing season. Developing management practices that make more efficient use of irrigation water is important for improving the sustainability of nursery crop production. Biochar, a byproduct of pyrolysis, can potentially increase the water-holding capacity and reduce water and nutrient leaching. In addition, the development of sensor-based irrigation technologies has made monitoring substrate moisture a practical tool for irrigation management in the nursery industry. The objective of this research was to determine the effect of switchgrass biochar on water and nutrient-holding capacity and release in container substrates of Buxus sempervirens L. × Buxus microphylla (‘Green Velvet’ boxwood) and Hydrangea paniculata (Pinky Winky® hardy hydrangea). Containers were filled with pine bark and amended with 0%, 10%, or 25% volume of biochar. Plants were irrigated when the volumetric water content (VWC) reached the water-buffering capacity set point of 0.25 cm3·cm−3. The sensor-based irrigation in combination with the low cost biochar substrate amendment increased substrate water-holding capacity and reduced irrigation requirements for the production of hydrangea, a high water use plant. Biochar application rate influenced irrigation frequency, which likely affected plant biomass for hydrangea, but boxwood dry weight was unaffected by biochar rate. Total irrigation applied was decreased by 32% in 10% biochar treatment without reducing hydrangea dry weight. However, in the 25% biochar treatment, total irrigation applied was reduced by 72%, whereas dry weight decreased by 50%. Biochar application reduced leaching volume and leaching fraction in both plants. Leachate analysis over the course of the 8-week experiment showed that the average mass of phosphate (PO4), potassium (K), and total carbon was greater in the leachate from containers that received 25% biochar compared with those receiving 0% or 10% biochar for both plant species. For hydrangea, mass of total nitrogen (TN) and nitrate (NO3) in leachate was not significantly affected by increasing the biochar rate. However, for boxwood, the mass of NO3 and TN was greater in the 25% biochar treatment leachate, whereas the mass of ammonium (NH4) was unaffected. In hydrangea, total nutrients lost from the containers was lower in biochar-amended containers (both 10% and 25% biochar) because of receiving a lower total volume of water. Amendment with biochar also affected concentration of phosphorus (P) and K, with the highest concentration in both leaf tissue and substrate from the 25% biochar application rate.

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Annual vinca [Catharanthus roseus (L.) G. Don ‘Peppermint Cooler’] plugs were transplanted to containers filled with Douglas fir [Pseudotsuga menziesii (Mirbel) Franco] bark (DFB) in May and June 2005 (Expts. 1 and 2, respectively). Treatments were arranged in a 2 × 3 factorial with two DFB ages (fresh and aged) and three micronutrient sources (DFB alone, 10% by volume yard debris compost, or 0.9 kg·m−3 Micromax fertilizer). Plants were measured for shoot dry weight and foliar color. Substrate and foliar samples of each plant were analyzed for 13 essential macro- and micronutrients plus substrate pH and EC. Douglas fir bark alone appears to provide sufficient micronutrients for annual vinca grown at pH 4.7 to 5.7 over a 2-month period. In Expt. 1 there were no differences in shoot dry weight or foliar color regardless of DFB age or micronutrient source. At the end of Expt. 2, plants in aged DFB were larger than those in fresh DFB, but differences were primarily the result of nitrogen availability. None of the treatments developed color symptoms that could be associated with micronutrient deficiency. Micronutrient availability in DFB should be considered in container fertilizer management plans.

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Liming agents (LAs) in irrigation water, typically associated with carbonates and bicarbonates of calcium (Ca) and magnesium (Mg), contribute to water alkalinity. Repeated application of LA to container crops can cause media-solution pH to rise overtime, that uncorrected, can lead to a nutrient availability imbalance that may be suboptimal for plant-growth due to nutrient disorder(s). To correct high levels of LA in irrigation water, growers can inject acid into their irrigation system to neutralize alkalinity. Therefore, a 52-week study was conducted using irrigation water, substrate, and plants from a commercial nursery in Florida that has a history of poor water quality and plant production problems related to high alkalinity irrigation water. The objectives of the study were to assess substrate pH, electrical conductivity (EC), and nutrients, and plant nutrition and growth for thyrallis (Galphimia gracilis Bartl.) to irrigation water acidification. Treatments consisted of irrigation water acidified with sulfuric acid (H2SO4) to neutralize 0% (control), 40%, or 80% of calcium carbonates (CaCO3) yielding a CaCO3 (meq·L−1)/pH levels of 5 [High Alkalinity (H-A)]/7.37, 3 [Medium Alkalinity (M-A)]//6.37, and 1 [Low Alkalinity (L-A)]//4.79, respectively. Substrate analysis by the 1:2 dilution method at the end of the study was significant (P < 0.05) for pH 6.2, 5.2, and 4.7 for the H-A, M-A, and L-A treatments, respectively, and for nutrients Ca, Mn, and Zn. Foliar nutrient levels were statistically significant (P < 0.05) for alkalinity treatment for Fe, K, Mn, P, and Zn. Alkalinity treatment was significant (P < 0.05) for growth, leaf greenness (by SPAD), and quality (by survey) with the M-A treatment producing more biomass, having greener leaves, and the highest aesthetic quality value than the H-A or L-A treatments. A qualitative survey of root systems at harvest showed that the M-A and L-A treatment root systems were greater than the H-A treatment based on visual side-wall root development. These data demonstrate that irrigation water acidification does alter substrate pH and nutrients and plant tissue nutrient levels and growth over a long-term production cycle typical for nursery crops.

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Controlling irrigation using timers or manually operated systems is the most common irrigation scheduling method in outdoor container production systems. Improving irrigation efficiency can be achieved by scheduling irrigation based on plant water needs and the appropriate use of sensors rather than relying on periodically adjusting irrigation volume based on perceived water needs. Substrate amendments such as biochar, a carbon (C)-rich by-product of pyrolysis or gasification, can increase the amount of available water and improve irrigation efficiency and plant growth. Previous work examined two on-demand irrigation schedules in controlled indoor (greenhouse) environments. The goal of this study was to evaluate the impact of these on-demand irrigation schedules and hardwood biochar on water use and biomass gain of container-grown Hydrangea paniculata ‘Silver Dollar’ in a typical outdoor nursery production environment. Eighteen independently controlled irrigation zones were designed to test three irrigation schedules on ‘Silver Dollar’ hydrangea grown in pine bark amended with 0% or 25% hardwood biochar. The three irrigation schedules were conventional irrigation and two on-demand schedules, which were based on substrate physical properties or plant physiology. Conventional irrigation delivered 1.8 cm water in one event each day. The scheduling of substrate-based irrigation was based on the soilless substrate moisture characteristic curve, applying water whenever the substrate water content corresponding to a substrate water potential of –10 kPa was reached. The plant-based irrigation schedule was based on a specific substrate moisture content derived from a previously defined relationship between substrate moisture content and photosynthetic rate, maintaining the volumetric water content (VWC) to support photosynthesis at 90% of the maximum predicted photosynthetic rate. Total water use for the substrate-based irrigation was the same as for the conventional system; the plant-based system used significantly less water. However, plant dry weight was 22% and 15% greater, water use efficiency (WUE) was 40% and 40% greater, and total leachate volume was 25% and 30% less for the substrate-based and plant-based irrigation scheduling systems, respectively, than for conventional irrigation. The 25% biochar amendment rate reduced leachate volume per irrigation event, and leaching fraction, but did not affect total water use or plant dry weight. This research demonstrated that on-demand irrigation scheduling that is plant based or substrate based could be an effective approach to increase WUE for container-grown nursery crops without affecting plant growth negatively.

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Greenhouse propagation of unrooted plant cuttings is characterized by short container cell height and high irrigation frequency. These conditions can result in high moisture level and low air content in soilless container substrates (“substrates”), causing delayed growth of adventitious roots and favoring root disease. The objective of this study was to quantify and compare substrate water and air relations for three propagation substrates (peat, rockwool, and phenolic foam) that varied widely in physical characteristics using four methods: 1) evaporation method with a tensiometer, 2) frozen column method, 3) gravimetric analysis, and 4) X-ray computed tomography (CT) analysis. Moisture retention curves based on evaporation (1) and the frozen column (2) resulted in differences for peat, but similar curves for rockwool and foam. The frozen column method was simple and low cost, but was constrained by column height for peat, which had a higher water potential compared with the other two substrates. Substrate porosity analysis at container capacity by gravimetric or CT methods were similar for volumetric water and air content (VWC and VAC) in rockwool and foam, but differed for peat for VWC and VAC. Gravimetric analysis was simple, rapid, and low cost for whole-cell analysis, but CT further quantified spatial water and air relations within the cell and allowed visualization of complex water and air relations in an image. All substrates had high water content at container capacity ranging from 67% to 91% VWC with 5% to 11% VAC in the short propagation cells, emphasizing the need for careful irrigation management.

Open Access

Because of limited supply of high-quality water, alternative water sources have been used for irrigation in water-scarce regions. However, alternative waters usually contain high salt levels, which can cause salt damage on salt-sensitive plants. A greenhouse study was conducted to evaluate the relative salt tolerance of 10 common ornamental taxa to saline water irrigation. The 10 taxa studied were Chaenomeles speciosa ‘Orange Storm’ and ‘Pink Storm’ (Chaenomeles Double Take); Diervilla rivularis ‘G2X885411’, ‘G2X88544’ (Diervilla Kodiak®, Black, Orange, and Red, respectively), and ‘Smndrsf’; Forsythia ×intermedia ‘Mindor’ (Forsythia Show Off®); Hibiscus syriacus ‘ILVOPS’ (Hibiscus Purple Satin®); Hydrangea macrophylla ‘Smhmtau’ and ‘Smnhmsigma’ (Hydrangea Let’s Dance® Blue Jangles® and Rave, respectively); and Parthenocissus quinquefolia ‘Troki’ (Parthenociss quinquefolia Red Wall®). Plants were irrigated with a nutrient solution at an electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solutions at EC of 5.0 or 10.0 dS·m−1 (EC 5 or EC 10) eight times on a weekly basis. The results indicated that the 10 ornamental taxa had different morphological and physiological responses to salinity. The C. speciosa and D. rivularis plants in EC 5 had severe salt foliar damage, whereas those in EC 10 were dead. Hibiscus syriacus ‘ILVOPS’ performed well in EC 5 treatment with a shoot dry weight (DW) reduction of 26%, but those in EC 10 had severe foliar salt damage. Hydrangea macrophylla, F. ×intermedia ‘Mindor’ and P. quinquefolia ‘Troki’ were the most salt tolerant with minor foliar salt damage. The two H. macrophylla cultivars had the highest shoot sodium (Na) and chlorine (Cl) concentrations with a visual quality of 3 (scale 0 to 5 with 0 for dead plants and 5 for excellent performance), indicating that H. macrophylla plants adapted to elevated salinity by tolerating high Na and Cl concentrations in leaf tissue. Forsythia ×intermedia ‘Mindor’ and P. quinquefolia ‘Troki’ had relatively low leaf Na and Cl concentration, indicating that both taxa are capable of excluding Na and Cl. Chaenomeles speciosa and D. rivularis were sensitive to salinity with great growth reduction, severe foliar salt damage, and high Na and Cl accumulation in leaf tissue.

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Soilless substrates are widely used for plant cultivation. However, little is known about how soilless substrate components, plant growth, or their interactions impact microbial communities in soilless media. The objectives of this study were to analyze microbial communities in typical pine bark substrates used for nursery crop production and determine the impacts of substituting peat with a compost substrate, and planting, on microbial community dynamics over a production cycle. Three soilless substrate mixtures were compared. The substrate mixes consisted of 80:20:0, 80:10:10, and 80:0:20 (volume:volume:volume) ratios of pine bark:peatmoss:leaf compost, respectively. One set of each treatment was planted with a single birch (Betula nigra ‘Cully’) liner and another set was not planted. The treatments (n = 3) were maintained in a nursery production setting, and samples were taken after 0, 1, 2, 3, and 4 months. Bacterial and fungal communities were characterized by sequencing polymerase chain reaction-amplified 16s rRNA genes and internal transcribed spacer regions. Initially, the two substrate mixtures that contained compost had more phyla than the substrate mixture that only contained peat and bark. After 1 month, microbial communities in all treatments contained similar phyla, but at different relative abundances based on the amount of compost they contained. Over time, Nitrosomonadaceae and Acetobacteraceae were the most abundant bacterial families in substrate mixes containing 10% and 20% compost, but they were absent from treatments without compost. The communities were dynamic and changed the most over the first 2 months. Microbial communities and their dynamics were similar between planted and unplanted treatments. Planting had less of an effect on microbial communities than compost amendment. Among the fungal communities, differences were observed based on both compost amendment and plant presence. Ascomycota and Basidiomycota were the most abundant fungal phyla and resembled those originally in the peat and compost, respectively. These findings could be used to understand the importance and dynamics of specific microbial communities present in substrate components and how they develop during greenhouse production.

Open Access

Two experiments were conducted with pansy (Viola ×wittrockiana Gams `Bingo Yello') to determine the relationship between foliar nitrogen (% of dry weight) (FN) and either sap nitrate concentration (SN) in petioles or SPAD readings of foliage. FN was highly correlated to SN throughout both experiments (r = 0.80 to 0.91). FN was poorly correlated to SPAD readings early in both experiments (r = 0.54 to 0.65), but more highly correlated later when visual symptoms of N deficiency were apparent (r = 0.84 to 0.90). SN determined with the Cardy sap nitrate meter was a reliable predictor of FN in pansy, while SPAD readings were only reliable after symptoms of N deficiency were visually evident. FN can be predicted with SN using the following equation: log(SN) = 0.47*FN + 1.6 [r 2 = 0.80, n = 132]. Growers and landscape professionals can use SN readings to predict FN levels in pansy, and thus rapidly and accurately diagnose the N status of their crop.

Free access