Recently developed capacitance soil moisture sensors are suitable for measuring volumetric water content (VWC, v/v) of soilless substrates in real time, useful for substrate moisture based–automated irrigation systems of horticultural crops. For capacitance sensors, a substrate-specific calibration is required for accurate VWC measurements, but sensor manufacturers typically provide only a general calibration for potting soil. However, the general calibration for potting soil is not indicative of the variety of soilless substrates. We investigated and compared the physical properties of various coir dust and perlite mix ratios (1:0, 8:2, 6:4, 4:6, 2:8, 0:1, v/v), and conducted individual substrate-specific VWC calibrations in the range from 0.1 m3·m−3 to near container capacity. Sensor outputs [in mV and analog-to-digital converter (ADC)] of various VWC levels of the specific substrates were collected with four EC-5 and GS3 sensors (Decagon Devices Inc., Pullman, WA) connected to a data logger with 2.5-V and 12-V excitation, respectively. Substrates with greater relative perlite contents had larger particles, and both the water-holding capacity and electrical conductivity (EC) were lower than the substrate mixes with more coir dust. All tested substrate mixes had linear relationship between EC-5 sensor output and VWC with high R 2 (>0.93) except in the case of 100% perlite, and their slopes were significantly different across the substrate mixes (P = 0.03). However, most of the substrate mixes had similar calibrations with estimated VWC differences within 0.06 m3·m−3. The GS3 sensor had the best fit with a logarithmic relationship between sensor output (in ADC) and VWC, and the slopes among the substrate mixes were not significantly different (P = 0.13). Furthermore, the soilless substrate calibration provided by the company differed from the substrate-specific calibration, resulting in considerable error (up to 0.18 m3·m−3 difference), during the measurement of the actual VWCs. Therefore, sensor- and substrate-specific calibration is required for accurate VWC measurements with capacitance sensors.
Yong Ha Rhie, Seonghwan Kang, and Jongyun Kim
Automated irrigation systems based on soil moisture sensor measurements can reduce water and fertilizer use while adequately meeting plant water requirements. In this study, the effects of substrate volumetric water content (θ, v/v) on the flowering of 17-month-old Doritaenopsis Queen Beer ‘Mantefon’ (from the time of deflasking) were examined. The plants were transplanted in plastic pots (10.5 cm width × 9.5 cm height) filled with sphagnum moss and the θ of sphagnum moss was maintained at 0.2, 0.3, 0.4, or 0.5 m3·m−3 using an automated drip irrigation system. Plants grown at a θ threshold of 0.2 m3·m−3 had thinner leaves and lower SPAD value than those grown at higher θ thresholds. The net CO2 uptake of the uppermost fully expanded leaf increased with increasing θ between 0.2 and 0.4 m3·m−3, but there was no significant difference in the net CO2 uptake between plants grown at 0.4 and 0.5 m3·m−3 thresholds. The number of flower buds at the time of the first open flower was lower in plants grown at θ thresholds of 0.2 and 0.3 m3·m−3 as compared with that in the plants grown at 0.4 and 0.5 m3·m−3 thresholds. Early flower abscission, flower bud dropping, and flower senescence during the 2 weeks after flowering occurred in 55% and 30% of the plants at 0.2 and 0.3 m3·m−3 thresholds, respectively, whereas plants at θ thresholds of 0.4 and 0.5 m3·m−3 had negligible flower abscission. Although vegetative growth parameters were similar among θ thresholds of 0.3 m3·m−3 or higher, plants grown at a θ threshold of 0.3 m3·m−3 produced fewer flowers than those grown at 0.4 and 0.5 m3·m−3 thresholds. During the 83-day experimental period, the system irrigated the plants ≈0.79, 1.93, 2.46, and 2.84 L/pot at θ thresholds of 0.2, 0.3, 0.4, and 0.5 m3·m−3, respectively. Overall, 0.4 m3·m−3 was considered to be an optimal threshold θ level for producing high-quality Doritaenopsis Queen Beer ‘Mantefon’ during the flowering period with most efficient water use.
Jongyun Kim, Marc W. van Iersel, and Stephanie E. Burnett
Many ornamental plant growers water excessively to reduce the risk of drought stress. Scheduling irrigation in greenhouses is challenging because there is little quantitative information about ornamental plant water requirements and how water use changes when plants are grown in varying greenhouse environmental conditions. Models to estimate the daily water use (DWU) of greenhouse crops may provide a useful tool to conserve irrigation water. Our objective was to develop a model to predict DWU based on plant age and easily acquirable environmental data. Two petunia (Petunia ×hybrida) cultivars, Single Dreams Pink and Prostrate Easy Wave Pink, were grown in different sized containers (diameter = 10, 12.5, and 15 cm) to quantify their DWU for 6 weeks. The substrate water content (θ, v/v) was maintained at 0.40 m3·m−3 using an automated irrigation system with capacitance soil moisture sensors. Every irrigation event was recorded by a data logger, and this information was used to calculate the DWU of the plants. On overcast days early in the experiment, plants used only 4.8 to 13.8 mL·d−1. The maximum DWU of ‘Single Dreams Pink’ was 63, 96, and 109 mL·d−1 in 10-, 12.5-, and 15-cm containers, respectively. Late in the experiment, ‘Prostrate Easy Wave Pink’ petunia used more water than ‘Single Dreams Pink’ because of their more vigorous growth habit. DWU was modeled as a function of days after planting (DAP), daily light integral (DLI), vapor pressure deficit (VPD), temperature, container size, and interactions between these factors and DAP (R 2 = 0.93 and 0.91 for ‘Single Dreams Pink’ and ‘Prostrate Easy Wave Pink’, respectively). Days after planting and container size were the most important factors affecting DWU and are indicative of plant size. Daily light integral was the most important environmental factor affecting DWU. These models, describing the DWU as a function of the DAP and environmental conditions, may be used as guidelines for accurately watering petunias in greenhouses and may improve irrigation scheduling.
Jongyun Kim, Seung Won Kang, Chun Ho Pak, and Mi Seon Kim
Variegated foliage plants are often used in interiorscaping in low light environments. The changes in leaf morphology and coloration of two variegated foliage plants, english ivy (Hedera helix ‘Golden Ingot’) and polka dot plant (Hypoestes phyllostachya), under various light intensities [photosynthetic photon flux (PPF) at 2.7, 6.75, 13.5, 67.5, and 135 μmol·m−2·s−1] were investigated to elucidate their optimum indoor light environment. Digital image analysis was used to quantify the changes in variegation area and color in CIELAB color space. The changes in leaf morphology (thickness, length:width) and coloration were different between the two species. In general, growth of both species increased with increasing PPF. English ivy showed no significant changes in leaf variegation under different PPF. Under low PPF (≤13.5 μmol·m−2·s−1), newly developed leaves of polka dot plant had reduced leaf variegation (44%, 72%, and 85% variegation loss under 13.5, 6.75, and 2.7 μmol·m−2·s−1, respectively). Anthocyanin content in leaves of polka dot plant also decreased with decreasing PPF, which reduced plants’ aesthetic quality. English ivy leaves under high PPF (≥67.5 μmol·m−2·s−1) displayed high brightness (L*) and yellowish green color (hue angle < 108°), which diminished its aesthetic value. Smaller leaf size and narrower shape of polka dot plant leaves under high PPF (≥67.5 μmol·m−2·s−1) also diminished its aesthetic value. Overall, english ivy performed well in a PPF range from 2.7 to 13.5 μmol·m−2·s−1, and polka dot plant required a PPF of at least 13.5 μmol·m−2·s−1 to maintain its red-purple variegation in the indoor environment.
Min Hyeong Kwon, Changwan Seo, Jongyun Kim, Moonil Kim, Chun Ho Pak, and Woo-Kyun Lee
The purpose of this study was to identify the current status and future development of children’s gardens within public gardens in the United States and to examine their roles as places for children to explore natural environments. This study identified 776 public gardens and examined 163 of those gardens using a comprehensive online survey. The sampled public gardens were widely distributed throughout the United States, although they were located primarily in the eastern and western regions of the United States. We found that 55% of the 163 public gardens that we investigated included a children’s garden at the time of data collection, and 26.4% planned to add a children’s garden in the near future. Children’s gardens found within public gardens were typically in a botanical garden and were added after the public gardens were formed. Most of the children’s gardens had a stated purpose of providing children with environmental education by allowing them to experience the natural environment through play. Most children’s gardens occupied a small proportion, less than 1 acre, of the overall size of a public garden. We also found that demographic and socioeconomic factors influenced the development of children’s gardens within public gardens and public gardens in general.
Min Hyeong Kwon, Jongyun Kim, Changwan Seo, Chiwon W. Lee, Eu Jean Jang, and Woo-Kyun Lee
This study examines the current status, implementation, and foci of children’s education programs as a subset of general audience-targeted public education programs offered by public children’s gardens in the United States. Children were a major target audience of the examined public gardens, followed by adults, families, and youth. Public children’s gardens tended to offer more programs overall compared with public gardens without children’s gardens. In addition, there was a greater diversity of children’s education programs offered (classified into 10 topics and 11 activities) in public children’s gardens. The most frequently offered topics were plants (39.1%), animals (22.0%), and art (11.3%). Observation was the most frequently offered activity (17.1%), followed by visual art (14.4%). However, the proportions of offered programs significantly differed across individual public children’s gardens. The subjects (i.e., topics and activities) offered by children’s education programs were more often directed toward younger children. Education coordinators and horticulture directors were asked about desired improvements to children’s education programs. A large number of respondents (50) indicated a need to develop programs with greater topical variety, revealing a desire to diversify programs. In conclusion, the results of this study indicate that it is important to diversify the natural environmental experiences of education programs for children through developing children’s gardens and age-specific education at public children’s gardens in the United States.