Nitrous oxide (N2O) emissions from soilless growing substrates are significantly greater per production area than crops grown in mineral soil. To understand and identify the N2O production pathways in soilless substrates, fir bark, peat, and peat:fir bark substrates were treated with labeled 15N fertilizers. The volumetric water content (VWC) of the soilless substrate was maintained near container capacity, and gas samples were collected every other day for 21 days and analyzed for 15N-N2O content. Fir bark and peat:fir bark substrates had significantly greater total N2O emissions than peat substrate when fertilized with NH4NO3. Denitrification was the main pathway of N2O emissions from all substrates and it was more pronounced in the fir bark and peat:fir bark substrates. In the peat substrate, the contribution of ammonia oxidation to N2O emissions started on day 11 and continued to increase until the end of the experiment, contributing to 6 % of the total N2O emitted from this substrate. Overall, reducing denitrification-derived emissions from soilless substrates is critical to mitigate the impact of container-plant production on global warming. Future research should focus on developing strategies to reduce these emissions.

The severe drought in California (2012-2016) generated significant public and government concern. State and local watering regulations were enacted to reduce residential and commercial water-use during the droughts. This study presents a comparison of residential runoff volumes before and after local landscape irrigation regulations were enacted during the droughts of 2008 and 2012-2016. Each sampling site (Folsom 1 and Folsom 2) was a storm drain outfall that drained a low-density residential catchment in the City of Folsom. Dry season runoff measured at the sampling sites represents neighborhood outdoor water waste, mainly from landscape irrigation. During the drought of 2012-2016, median runoff flows were significantly reduced after local landscape irrigation regulations were enacted. The daily runoff pattern was also highly influenced by regulation, with reductions of daily peak runoff flows on 4-5 days in a week after watering regulations were enacted. The number of peak flow events in the daily runoff pattern were reduced during this period. In addition, a significant reduction in mean runoff volume occurred. Based on these results, the watering regulations enacted by the City of Folsom had a positive effect on reducing urban runoff from residential neighborhoods during the dry season. As the results are from monitoring sites in a relatively small geographical area, further work should evaluate reductions in irrigation runoff from other California locations to determine if this is a localized phenomenon.

Urban waterways degradation due to runoff from residential areas can be reduced by adopting best management practices (BMPs) for irrigation, fertilizer, and pesticide use. Although stormwater runoff from urban areas has been studied extensively, we focus on single-family residential land use specifically. Outreach to individual households may have a measurable impact since decisions are being made here. We surveyed households to evaluate the effectiveness of education and outreach campaigns on self-reported use of water and chemicals and evaluated whether self-reported behaviors were reflected in the quality and quantity of water draining from the study areas before and after outreach efforts. Our research was conducted in California, which has a Mediterranean climate with distinct wet and dry periods. Runoff from residential landscapes during the dry season enters waterways undiluted by rainwater, making this runoff particularly detrimental to receiving waters. No significant differences in behavior and BMP adoption from before and after the education and outreach campaign was found. These results are not atypical and may be explained by several factors including the population approach to the survey, lag times between outreach and measurable effects, and the need for a critical threshold of adoption to be met for effects to be measurable.

Increased urban and suburban populations in the arid western United States have resulted in more water demand; however, water availability in the region has become limited because of inadequate precipitation. Recent droughts have led to restrictions on irrigating landscape plants. Garden rose (Rosa ×hybrida) is commonly used as flowering plants in residential landscapes, but its drought tolerance has not been widely studied. The objective of this study was to determine the impact of reduced irrigation frequency on visual quality, plant growth, and physiology of five garden rose cultivars, including ChewPatout (Oso Easy® Urban Legend®), Meibenbino (Petite Knock Out®), MEIRIFTDAY (Oso Easy® Double Pink), Overedclimb (Cherry Frost™), and Radbeauty (Sitting Pretty™). Twenty-four plants of each rose cultivar were established in a trial plot at Utah Agricultural Experiment Station Greenville Research Farm (North Logan, UT, USA) in Summer 2021. Plants were randomly assigned to one of three deficit irrigation treatments for which irrigation frequencies were calculated using 80% reference evapotranspiration (ETO) (high), 50% ETO (medium), and 20% ETO (low). The total volumes of irrigation water applied to each plant were 345.6, 172.8, and 43.2 L for the high, medium, and low irrigation frequencies, respectively, during the deficit irrigation trial from 12 May to 30 Sep 2022. Root zones were wetted more frequently as irrigation frequency increased from low to high irrigation frequencies. Decreased irrigation frequency increased the number of visibly wilted and damaged leaves on all rose cultivars. However, only ‘Meibenbino’ and ‘MEIRIFTDAY’ exhibited a reduction in overall appearance under decreased irrigation frequency. The relative growth indices of both ‘Meibenbino’ and ‘MEIRIFTDAY’ decreased by 6%, whereas the dry weights of their leaves decreased by 37% and 36%, respectively, as irrigation decreased from high to low frequencies. Roses in this study appeared to decrease stomatal conductance up to 51% when irrigation decreased from high to low frequencies, or when air temperature increased. ‘Meibenbino’ and ‘MEIRIFTDAY’ exhibited unacceptable overall appearance, growth reduction, and higher leaf–air temperature differences, and they were less tolerant to reduced irrigation. Although the ‘Radbeauty’ maintained plant growth under the reduced irrigation frequency, the large leaf size led to a more visibly wilted appearance and the potential for heat stress, thus impairing visual quality. ‘ChewPatout’ and ‘Overedclimb’ were most tolerant to deficit irrigation at 20% ETO and maintained plant growth with acceptable visual quality and lower leaf temperatures when they received one irrigation during the growing season.

Available water for urban landscape irrigation is likely to become more limited because of inadequate precipitation and the ever-increasing water demand of a growing population. Recent droughts in the western United States have also increased the demand for low-water-use landscapes in urban areas. Penstemon species (beardtongues) are ornamental perennials commonly grown in low-water-use landscapes, but their drought tolerance has not been widely investigated. The objectives of this study were to determine the effects of water availability on the morphology, physiology, and canopy temperature of Penstemon barbatus (Cav.) Roth ‘Novapenblu’ (Rock Candy Blue ® penstemon), P. digitalis Nutt. ex Sims ‘TNPENDB’ (Dakota™ Burgundy beardtongue), P. × mexicali Mitch. ‘P007S’ (Pikes Peak Purple ® penstemon), and P. strictus Benth. (Rocky Mountain penstemon). Twenty-four plants of each penstemon species were randomly assigned to blocks in an automated irrigation system, and the substrate volumetric water content was maintained at 0.15 or 0.35 m 3 ⋅m −3 for 50 days. The decreased substrate volumetric water content resulted in a decreased aesthetic appearance of the four penstemon species because of the increased numbers of visibly wilted leaves and chlorosis. Plant growth index [(height + (width 1 + width 2)/2)/2], shoot number, shoot dry weight, leaf size, and total leaf area also decreased as the substrate volumetric water content decreased, but the root-to-shoot ratio and leaf thickness increased. Photosynthesis decreased, stomatal resistance increased, and warmer canopy temperatures were observed when plants were dehydrated. Additionally, as substrate volumetric water content decreased, the leaf reflectance of P. barbatus and P. strictus increased. Penstemon digitalis , which had the highest canopy–air temperature difference, was sensitive to drought stress, exhibiting a large proportion of visibly wilted leaves. Penstemon ×mexicali , which had the lowest root-to-shoot ratio, had the lowest shoot water content of the species studied and more than 65% of leaves visibly wilted when experiencing drought stress. Penstemon barbatus and P. strictus , native to arid regions, exhibited lower canopy–air temperature differences and better aesthetic quality than the other two species. Under the conditions of this study, Penstemon barbatus and P. strictus exhibited better drought tolerance than P. digitalis and P. × mexicali .

Many specialty crop growers are transitioning high-value crops from in-ground production to soilless culture due to the diminishing availability of fumigants, increasing pest pressure, extreme weather, and the need for flexible production practices. The objective of this study was to determine the research and educational needs of specialty crop growers who are transitioning to soilless substrates. North American growers were surveyed using an online instrument that incorporated Likert-type statement matrices, open-ended questions, and demographic questions. Additionally, two virtually led focus groups were conducted to further expand upon the quantitative findings with descriptive data. Respondents indicated the most important factors in considering whether to adopt soilless substrates were improving, managing, and reducing overall plant quality, disease management, and crop loss, respectively. The most important research needs were understanding the effects of substrates on crop quality and uniformity, fertilizer management, and economic costs and benefits/return on investment. In both the grower survey and focus groups, crop quality and uniformity were among the highest-scored responses. Food safety, disease and pest management, consumer perception, substrate disposal-related issues, transportation, and return-on-investment were also identified as important factors when considering soilless substrates.

To reduce nitrate contamination of groundwater in intensive agricultural production areas, crop producers should identify nitrogen (N) inputs and outputs to calculate potential N available for leaching into groundwater. However, poor understanding of N fate in container plant production may result in inaccurate estimation of potentially leachable N. To improve understanding of container-applied N fate, an experiment was conducted to measure N inputs and outputs from a woody ornamental plant (Lagerstroemia indica 'Whitt II') production system fertilized with controlled-release and surface-applied fertilizer. Two experimental bed types, polyethylene-lined and unlined, were installed at a production nursery in California. Measured N inputs included: the substrate, with fertilizer and roots, and irrigation water N. Outputs included: N remaining in the substrate and plant shoots at the end of the production cycle, nitrous oxide-N gas lost from the substrate and bed soil, and aqueous N lost in runoff during the production cycle. There was a significant difference in runoff N losses from the lined and unlined beds. The difference in runoff N lost between bed types was the amount of N infiltrating into the soil below the growing bed surface. The majority of input N either remained in the growing substrate (57%) at end of production cycle or was taken up by the plant shoots (5%). Nitrous oxide-N lost from the growing substrate and the bed soil was 1.5% and 0.01% of input N, respectively. Runoff and soil infiltration N accounted for 6.5% and 2.4% of input N, respectively. Unaccounted N was 27.7% of input N and is attributed to complete denitrification. Future work should address the amount of aqueous N lost from the growing substrate to reduce surface and groundwater contamination.

Many arid lands across the globe are experiencing more frequent and extreme droughts due to warmer temperatures resulting from climate change, less predictable precipitation patterns, and decreased soil moisture. Approximately 60–90% of household water is used for urban landscape irrigation in the western United States, necessitating the establishment of landscapes using drought-tolerant plants that conserve water. Shepherdia ×utahensis (hybrid buffaloberry) is a drought-tolerant plant with dense leaf trichomes (epidermal appendages) that may limit excessive water loss by transpiration. However, little is known about how S. ×utahensis regulates leaf heat balance when transpirational cooling is limited. The objective of this research was to investigate the effects of substrate water availability on plant growth and development and trichome density of S. ×utahensis. Ninety-six clonally propagated plants were grown using an automated irrigation system, and their substrate volumetric water contents were controlled at 0.05–0.40 m3·m−3 for 2 months. Results showed that water stress impaired plant growth and increased the proportion of visibly wilted leaves. Shepherdia ×utahensis acclimates to drought by reducing cell dehydration and canopy overheating, which may be accomplished through decreased stomatal conductance, smaller leaf development, leaf curling, increased leaf thickness, and greater root-to-shoot ratio. Leaf trichome density increased when stem water potential decreased, resulting in greater leaf reflectance of visible light. Cell and leaf expansion were restricted under water stress, and negative correlations were exhibited between epidermal cell size and trichome density. According to our results, plasticity in leaves and roots aids plants in tolerating abiotic stresses associated with drought. Acclimation of S. ×utahensis to water stress was associated with increased trichome density due to plasticity in cell size. Dense trichomes on leaves reflected more lights which appeared to facilitate leaf temperature regulation.

The objective was to investigate water use per area and its relationship to reference evapotranspiration (ETO) at a large-scale container-grown plant nursery in California. Monthly applied irrigation was recorded during 2016 and 2017. Irrigation runoff was captured and measured from impervious material-lined production areas and runoff channels. A runoff coefficient for irrigation volume was developed for periods absent of precipitation. For periods when runoff volume data did not exist, estimated runoff volume was determined by multiplying the runoff coefficient by applied irrigation volume. Estimated runoff volume was subtracted from total applied irrigation volume to estimate total nursery water use. Total nursery water use was divided by the nursery production area to estimate nursery evapotranspiration (ETN). Monthly ETo was recorded from two California Irrigation Management Information System (CIMIS) stations, #44 and #240, 19 km and 17 km from the nursery site, respectively. A monthly nursery coefficient (K-N) was derived by dividing monthly ETO by monthly ETN, a similar calculation to crop coefficient (K-c). Monthly non-recovered irrigation volume ranged from 6,304 to 69,832 m(3) with a mean of 32,066 m(3) during 2016-2017. Monthly non-recovered irrigation volume was greater during periods of higher ETO. Estimated monthly K-N at the nursery was 0.21 to 0.56. Although runoff conduits were lined with impervious material, infiltration and evaporation did occur and accounting for those losses would further reduce K-N.

Carbon dioxide (CO2), nitrous oxide (N20), and methane (CH4) flux from a fir bark substrate was estimated at an ornamental plant nursery in California during a typical 81 -day production cycle. The soilless substrate consisted of 4:1 (v:v) fir bark:sand, incorporated with 3.47 kg m-3 Apex 9-2-0 sulfur-coated urea and 4.51 kg m-3 Osmocote Plus 15-9-12 controlled release fertilizer. On day zero, Lagerstroemia indica 'Whitt II' plants from number one containers were planted individually into number five containers filled with substrate. On day three, the substrate was topdressed with 34.7 g of 20-9-9 urea -formaldehyde fertilizer. Carbon dioxide and N20 sampling occurred on four days during the first week and once each week thereafter for 14 total sampling days. Methane flux sampling occurred once each week starting on day 18, for nine total sampling days. Eight pots were randomly selected for sampling to measure CO2 and N20 flux and four of these were used to determine CH4 flux as well. Each flux sample consisted of four gas samples taken at 10 -min intervals from a static -chamber in each pot and held in Exetainer vials until analyzed by gas chromatography. Gas fluxes were calculated for each pot using the `gasfluxes' package in R. Mean gas fluxes were -1.5 mg CH4-C m-2 h-1, 467 mg CO2-C m -2 h-1, and 3.6 mg N20 -N m -2 h-1. Low methane concentration in the gas samples and high mean p -value (p=0.24) of methane flux indicated that the CH4 fluxes were negligible. Carbon dioxide and N20 fluxes were highly variable among samples and over the 81 -day study. Future work to mitigate greenhouse gases from soilless substrate should focus on N20 emissions since net CH4 flux is negligible and CO2 generated from the fir bark growing media is not considered a greenhouse gas.

ISHS II International Symposium on Growing Media, Soilless Cultivation, and Compost Utilization in Horticulture Soilless substrate science: a North American needs assessment to steer soilless substrate research into the future

This research aimed to estimate methane (CH4) and nitrous oxide (N2O) fluxes and subsequent global warming potential (GWP) for a Douglas fir (Pseudotsuga menziesii) bark-based substrate production system. The fir bark-based substrate had controlled release fertilizer (CRF) incorporated with differing amounts of surface-applied fertilizer. In a nursery study and greenhouse experiment, gas flux samples were regularly collected. Total cumulative N2O emissions and GWP were greatest from the greenhouse treatment with the most surface-applied fertilizer. A regression model indicated that significant predictors of N2O flux were the pour-through extract ammonium (NH4-N) and nitrate (NO3-N) concentrations, volumetric water content (VWC), and substrate temperature. The net CH4 flux was negligible for all treatments during both studies. The N2O-N seasonal emission factor was 2.58-3.08, greater than for soil-grown California horticultural crops. These results indicate that N2O is the major greenhouse gas from a soilless substrate and should be the focus of mitigation efforts.

Recapture and recycling of irrigation water is often required to meet enormous water demands at horticultural nurseries. We tested four water types associated with a recycled irrigation system at a commercial container nursery in southern California for presence of oomycete plant pathogens from July 2015 to December 2017. These water types included: the main source of water originating from a reservoir, retention water from an on-site collection pond, irrigation water received by different growing areas within the nursery, and irrigation runoff captured in polyethylene sheet-lined runoff channels. The genera Phytophthora, Pythium, and Phytopythium together contributed more than 85% of the total oomycete population detected in the recycled irrigation system. The Phytophthora and Pythium genera were represented by member species from nine (1-4, 6-10) and eight (A, B, D-F, H-J) different subgeneric clades, respectively. Incoming water sourced from the reservoir was found to harbor known plant pathogens such as Phytophthora citricola-complex, P. capsici-cluster, P. tropicalis, P citrophthora-cluster, P. nemorosa-cluster, P. riparia, P. cryptogea-complex, P. parsiana-cluster, P. sp. nov. aff. kernoviae, Pythium dissotocum-complex, Py. oligandrum-cluster, Py. irregulare, and Phytopythium litorale. Runoff water showed the highest oomycete species richness and frequency of detection with both filtration and leaf baiting methods. In addition to plant pathogens, oomycete fish pathogens such as Aphanomyces laevis, Pythium chondricola-complex, Pythium flevoense-complex, and Saprolegnia diclina-complex were also detected in greater abundance in the recycled irrigation water. The oomycete species richness in the runoff water was correlated with several environmental parameters such as soil temperature. Greater oomycete richness in incoming water was associated with higher soil temperatures, whereas richness in runoff declines with increasing soil temperature, likely suggesting connections to weather-dependent nursery operations. (C) 2020 Elsevier Ltd. All rights reserved.

The genus Cotoneaster Medik. encompasses hundreds of woody shrub species whose growth habits range from prostrate to upright. Cotoneaster species are desirable in landscapes for their low maintenance requirements and year-round aesthetic interest. However, the health and aesthetic quality of many Cotoneaster species is threatened by the bacterial disease "fire blight," caused by Erwinia amylovora (Burrill 1882) Winslow et al. 1920. This study assessed fire blight resistance of three new Cotoneaster genotypes (H2011-02-001, H2011-01-002, and H2011-02-005) bred for disease resistance and two commercially available cultivars, Cotoneaster dammeri 'Coral Beauty' and C. dammeri 'Lowfast' under field conditions. Fourteen replicates of each taxa were planted in Davis, CA (USDA climate zone 9; Yolo silty clay loam soil) in May 2017. For plant establishment, irrigation at 100% of reference evapotranspiration (ETo) was provided during the first summer after planting. In the second summer after planting (2018), plants received deficit irrigation at 50% of ETo. In June 2018, seven replicates of each taxa were artificially inoculated with a local isolate of E. amylovora by bisecting the two youngest leaves on one branch with scissors dipped in a bacterial suspension of 109 CFU mL(-1). An additional seven replicates were artificially inoculated using the same method with sterile deionized water as a control. Fire blight susceptibility was assessed by calculating the percent shoot necrosis (PSN = 100x(lesion length/total branch length)) once a week for eight weeks after inoculation. Taxa with a PSN greater than 0% were considered susceptible and taxa with a PSN equal to 0% were considered resistant. H2011-02-005 (mean PSN=14.5 +/- 8.4%), C. dammeri 'Coral Beauty' (mean PSN=4.4 +/- 4.4%), and C. dammeri 'Lowfast' (mean PSN=12.3 +/- 11.1%) showed varying levels of susceptibility. H2011-02-001 and H201101-002 showed no necrosis (mean PSN=0.0 +/- 0.0%) and were considered resistant. The two resistant genotypes are candidates for new ornamental introductions where fire blight is prevalent.

Potted poinsettia (Euphorbia pulcherrima) is an important commercial commodity for the U.S. floriculture industry. The production of poinsettia demands intensively managed light control, heat, fertilizer, and water; inhibiting elongation with plant growth regulators, and protecting plants from diseases and pests with pesticide applications. Excessive irrigation creates pollution, promotes disease, and is expensive. Sensor-based control systems can optimize irrigation schedules. Irrigation management is crucial in nursery production of poinsettias because water is a limited resource and agricultural runoff is monitored in many states across the United States. By pairing environmental sensors with sensors that continuously monitor plant transpiration, we can determine how plant water use and water stress fluctuate with environmental and physiological demands. We hypothesized that continual measurements of sap flow could be correlated with environmental sensors to develop a new water stress index (WSI), which can deliver the benefits of detecting water stress that might affect the quality of potted poinsettias. To test this hypothesis, rooted cuttings of poinsettia (E. pulcherrima cv. Prestige Red) were individually potted into twelve 11-L black plastic nursery pots. Potted plants were grown in a naturally illuminated temperature-controlled glasshouse. The 12 plants were randomly assigned one of three watering treatments: weekly, biweekly, and triweekly irrigation. From the data collected, we were able to create a WSI that correlated available soil moisture with the difference between the expected transpiration with actual transpiration rates. Our results suggest that the plants in the weekly treatment group did not experience water stress until 0.3 m3·m–3 volume water content indicated by <0.2 WSI. These results support previous research that found 0.1 to 0.3 m3·m–3 can be stressful soil moisture conditions for greenhouse-grown crops. Results also show that for substrates with similar substrates that irrigation set points can be reduced to 0.2 m3·m–3 for improved irrigation efficiency.

Nursery, floriculture, and propagation production accounted for 79% ($13.3 Billion) of 2017 ornamental specialty crop production in the United States. Access to high quality water sources is increasingly limited for irrigating these economically significant crops. Given the production, environmental, and economic issues associated with the use of water-including recycled, reclaimed, surface, and ground water-it is critical to develop sustainable runoff, containment, and remediation technologies, and to identify alternative sources of water. To better understand current practices and future water-related needs as perceived by grower stakeholders, an online survey was distributed nationally and five in-depth round table discussion sessions were conducted at the Mid-Atlantic Nursery Trade Show, Gulf States Horticultural Expo, California Grown Show, American Hort's Cultivate, and the Farwest Show with a total of 36 individual industry participants. A team of research and extension specialists facilitated by a Specialty Crops Research Initiative Planning Grant (NIFA Project # 2011-51181-30633) analyzed and concisely summarized the results from the survey and the round table discussions. Research priorities related to water management identified by stakeholders revolved around six themes: (1) recycled water infrastructure and management; (2) contaminants; (3) plant health and water quality; (4) water treatment technologies; (5) competing and complementary water uses; (6) societal perception of agricultural water use.

Water conservation has become a critical issue in urban landscapes in summer-dry climate regions where irrigation must be applied to keep plants healthy. Part of the strategy for reducing landscape water use is incorporating plants with low water needs into the design. To implement this, landscape professionals need information on which available plants can perform acceptably in the landscape on low water, but research-based plant water-use information is often unavailable. Since 2005, University of California researchers have performed trials to evaluate in-ground landscape plant performance on four levels of reduced irrigation, including 10 Rosa hybrida cultivars between 2009 and 2016: ‘Aushouse’, ‘Gruss an Aachen’, ‘KORbin’, ‘KORelamba’, ‘KORfloci01’, ‘KORsixkono’, ‘KORsteimm’, ‘Meidrifora’, ‘Meigalpio’, and ‘Meijocos’. The irrigation treatments were based on levels of reference evapotranspiration (ET(0)) at 20, 40, 60, and 80% of ET(0) in a water budget model using data from a nearby weather station in the California Irrigation Management Information System. After one year of establishment irrigation at 100% of ET(0), irrigation treatments were applied during the second year to six plants of each cultivar on each treatment. Data taken monthly were growth measurements and quality ratings of foliage, flowering, pest tolerance, disease resistance, and overall appearance. Statistical analyses using ANOVA and Tukey’s HSD showed no significant differences in growth between treatments at p≤0.05. For several cultivars, some or all quality parameters were higher on one or more levels of irrigation than others. While some cultivars performed best on the 60% ET(0) treatment, most performed acceptably at 40 and 20% of ET(0) as well. These data have been used to make recommendations for grouping plants by water need in the landscape and in facilitating optimization of landscape water applications

Drainage-system management relies on results from urban stormwater models; errors in these models may have serious implications. Inaccurate field data or overly simplified models may cause the complex response of an urban basin to a rainfall event to be inadequately represented. Before undertaking expensive studies to gather and analyze additional data, it is reasonable to understand what enhancement in model performance would result if individual uncertainties could be decreased. This paper uses data collected during field monitoring campaigns to calibrate and validate a hydrologic and sediment-transport model within the Storm Water Management Model (SWMM). Solid accumulation and disappearance rates were identified as factors generating the highest model sensitivity. A generalized evaluation matrix is presented that considers both the uncertainty in input variables and the associated sensitivity in model response to inform model performance expectations and guide investments in model improvement toward actions with maximum benefit.