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A primary goal of undergraduate education is to provide a comprehensive and diverse educational experience to prepare and promote student success in their professional and personal pursuits. Increased academic success and program connectivity have been demonstrated when undergraduate students are engaged in research early in their degree programs. Despite the known benefits of undergraduates engaging in research, there are challenges associated with conducting undergraduate research programs. Reported barriers include the lack of student knowledge about research methods, lack of preparedness, and lack of student identification and understanding of their specific interests which may not facilitate research ideas and affinity to conduct research. Additional challenges are related to the lack of faculty resources (e.g., time, specific equipment, research space, etc.), the ability to train and supervise undergraduates who may have very limited or no research experience and those students who are true beginners lacking foundational skills. Moreover, involving, engaging, and supporting underrepresented students (e.g., first-generation college students, females, ethnic minorities) in undergraduate research experiences can require different approaches for mentors to be effective. The “Engaging Undergraduate Students in Research” workshop was organized by the Vice Presidents of the American Society for Horticultural Science (ASHS) Research and Education Divisions at the ASHS 2022 Annual Conference in Chicago, IL, USA. The workshop featured three speakers who described their experiences engaging undergraduate students in research. After each speaker provided comments for ≈5 minutes, the workshop attendees self-selected into three breakout groups with the speakers for roundtable discussions related to engaging students in research through coursework, engaging students via formal research projects, and engaging underrepresented students in research. After the breakout group discussions, a summary was given by each group, and whole group discussions and comments were facilitated. This is a summary of the information discussed and shared during the workshop, along with information that can assist faculty with developing and implementing undergraduate research experiences.

Hydroponic leafy green production offers high productivity and quality of crops but requires good management of pH and electrical conductivity (EC) to optimize the nutrient uptake. Nutrient solution pH is typically managed between 5.5 and 6.5, whereas lowering pH to more acidic range (e.g., −1) significantly improved but was still lower than those in the control (pH 5.5 and EC 1.4 dS·m−1), respectively. Plant tissue analysis showed that lowering pH to 4.5 significantly reduced tissue concentrations of P, K, Ca, Mg, S, Cu, Mn, and Zn compared with those in the control. Under low pH and increased EC treatment (pH 4.5 and EC 3.4 dS·m−1), all dry leaf nutrient concentrations were similar or higher than those of the control, except Mg and Zn, which showed a lower concentration than the control with a weak significance (P < 0.06). This suggests that additional optimization of nutrient formula might further improve the spinach growth at low pH. Together, our results will help to develop a new and low-cost nutrient management methodology to produce leafy greens hydroponically.

Strawberry (Fragaria ×ananassa) production practices followed by growers in the United States vary by region. Understanding the challenges, needs, and opportunities in each region is essential to guide research, policy, and marketing strategies for the strawberry industry across the country, and to enable the development of general and region-specific educational and production tools. This review divided the United States into eight distinct geographic regions and an indoor controlled or protected environment production system. Current production systems, markets, cultivars, trends, and future directions for each region are discussed. A common trend across all regions is the increasing use of protected culture strawberry production with both day-neutral and short-day cultivars for season extension to meet consumer demand for year-round availability. All regions experience challenges with pests and obtaining adequate harvest labor. Increasing consumer demand for berries, climate change-induced weather variability, high pesticide use, labor and immigration policies, and land availability impact regional production, thus facilitating the adoption of new technologies such as robotics and network communications to assist with strawberry harvesting in open-field production and production under controlled-environment agriculture and protected culture.

Understanding of environmental factors affecting various aspects of plant growth and development is crucial in plant factories' design and operation. This chapter first defines vegetative growth (shoots and root growth) and then discusses the typical abiotic environmental factors (temperature, light intensity, light quality, photoperiod, humidity, carbon dioxide concentration, air current speed, and nutrient and root-zone environment) affecting plant growth and development. Then transpiration and translocation of sugar are briefly described using the general physiological understanding of water potential and the sink–source relationship.

Vegetable grafting is a labor-intensive operation with many management decisions. Labor management and resource planning are critical allocations in grafting nurseries, yet optimization is challenging due to the dynamic nature of workers’ performance in vegetable seedling propagation. To this end, we developed a simulation-based optimization framework for labor management to optimize labor allocation. This approach was evaluated by comparing its result with those suggested by selected domain experts (a plant scientist and a nursery manager). Furthermore, the simulation models were validated with a dataset from a developing tomato grafting company. Simulation-based optimization is demonstrated as an effective approach to find the optimal/near optimal labor allocation for horticultural nurseries, where discrete event simulation is used to represent the dynamics of the grafting work environment and meta-heuristics are used to devise optimal/ near optimal resource allocation strategies. Results reveal that a potential annual savings between $2,510 (0.6%) and $97,388 (20%) can be achieved for a grafting facility of 6 million plants per year. Keywords: Simulation-based optimization, Grafting, Labor allocation, Discrete event simulation.

Intumescence injury is a physiological disorder characterized by watery tumors on a leaf surface associated with abnormal cell enlarge ment and cell division. This problematic intumescence injury has been observed on susceptible cultivars of tomato when grown under an ultraviolet radiation (UV) deficient light environment. In this study, different doses of UV-B radiation were applied after each photoperiod for ‘Beaufort’ interspecific tomato rootstock seedlings (Solanum lycopersicum × S. habrochaites) grown under light emitting diodes (10% blue and 90% red photon flux). The percent number of leaves exhibiting intumescences on leaves decreased linearly with increasing UV-B dose (measured in a 300–320 nm range) in the range examined (0–6.7 mmol m−2 d−1 or 0–2.6 kJ m−2 d−1 achieved by 0.31 μmol m−2 s−1 or 0.12 W m−2 UV-B photon flux for 0–6 h). The severity of intumescence injury was also linearly decreased by increasing UV-B dose. The intumescence incidence as well as severity was the highest in the non-treated control (66.0% leaves showing injury and 2.5–3.8 severity score out of 5) and the lowest (36.1% leaves showing injury and 0.6–1.6 severity score) at the highest dose of 6.7 mmol m−2 d−1 UV-B. The shoot dry weight of seedlings increased by 119% under the highest UV-B dose compared with that of non-treated control. T5-type white fluorescent lamps used for comparison emitted a moderate dose of UV-B (4.3 mmol m−2 d−1 at 0.07 μmol m−2 s−1 for 18 h d−1) and induced a moderate level of intumescent injury. Linear regression suggests that the UV-B dose eliminating intumescence was likely at around 12.3–14.0 mmol m−2 d−1 (4.7–5.3 kJ m−2 d−1), less than a UV-B dose received outdoors on a typical clear summer day. This level of UV-B is achievable under T12-type fluorescent lamps which emit more UV-B and explains why we typically do not see intumescence under T12 fluorescent lighting. The results obtained in this study will help to avoid intumescence in tomato plants grown under controlled environments.

Electric lamps are widely used to supplement sunlight (supplemental lighting) and daylength extension (photoperiodic lighting) for the production of horticultural crops in greenhouses and controlled environments. Recent advances in light-emitting diode (LED) technology now provide the horticultural industry with multiple lighting options. However, growers are unable to compare technologies and LED options because of insufficient data on lamp performance metrics. Here, we propose a standardized product label that facilitates the comparison of lamps across manufacturers. This label includes the photosynthetically active radiation (PAR) efficacy, PAR conversion efficiency, photon flux density output in key wave bands, as well as the phytochrome photostationary state (PSS), red/far red ratio, and graphs of the normalized photon flux density across the 300–900 nm wave band and a horizontal distribution of the light output.

Effect of light intensity and plant sink/source balance on strawberry plant photosynthesis was investigated in this study. Previous research (Inaba, 2007) showed diurnal decline of photosynthetic capacity in strawberry, indicating potential presence of negative photosynthesis feedback. We conducted monthly measurements of leaf net photosynthetic rate (Pn), stomatal conductance, intercellular CO2 concentration (Ci) and transpiration rate in strawberry cultivars 'Albion' and 'Nyoho' in greenhouse, during winter/spring production season. Measurements were taken hourly from 9 am to 4 pm using portable leaf photosynthesis measurement system under 1000 µmol m-2 s-1 photosynthetic photon flux (PPF) and 400 µmol mol‐1 CO2. Pn measurements were conducted for 'Speedella' tomato for comparison. Sink load of flowers and fruits was estimated from number of flowers and fruits at the measurement day and the fruit yield from the consecutive 4 weeks. Potential source strength was evaluated based on number of leaves and the daily light integral (DLI, 400-700 nm). We observed seasonal changes in maximum Pn, as well as diurnal change in Pn in both strawberry cultivars. As expected, in tomato, Pn was relatively constant regardless of time of day or month. Analysis showed significant positive correlation between estimated ratios of sink/source and slopes of linear equations applied for diurnal change in Pn. Also, Pn was negatively correlated with Ci but not significantly correlated with vapor pressure deficit in greenhouse, suggesting diurnal decline in Pn was likely due to negative feedback of photosynthesis and not to water stress. Results indicate morning hours as critical time for promoting photosynthesis in strawberry, when negative feedback of photosynthesis is occurring. Understanding diurnal change of plant photosynthetic capacity could lead to develop practices in strawberry production under controlled environment in order to maximize production.

Greenhouse strawberry production is gaining interest in North America where field production is the primary source of fruit. Issues of off-season greenhouse strawberry production include tipburn, an environmentally induced localized calcium deficiency. Tipburn often increases when nighttime relative humidity (RH) is low (high vapor pressure deficit, VPD) from nighttime heating or venting with dry air in arid climate. High nighttime humidity ( 3 h nighttime high RH (

Low-temperature storage is a technique to hold seedlings for a short period of time to adjust the production schedule of young seedlings. Labor-intensive grafting propagation can potentially benefit from the effective use of this technique to minimize peak labor inputs. Watermelon (Citrullus lanatus) seedlings are generally chilling sensitive and therefore difficult to store at low temperatures. However, the rootstocks used for watermelon grafting, interspecific squash (Cucurbita maxima × Cucurbita moschata) and bottle gourd (Lagenaria siceraria) are known to be chilling tolerant. To examine the influence of rootstocks on storability of watermelon seedlings, young seedlings of ‘Tri-X-313’ seedless watermelon grafted onto ‘Strong Tosa’ interspecific squash, ‘Emphasis’ bottle gourd, and ‘Tri-X-313’ watermelon as rootstock were placed for 2 or 4 weeks under 12 °C air temperature and 12 μmol·m−2·s−1 photosynthetic photon flux (PPF). Nongrafted watermelon seedlings were also treated in these same conditions. In addition, nonstored (grafted and nongrafted) seedlings were prepared for comparison. Regardless of seedling type (nongrafted or grafted with different rootstocks), all seedlings stored for 2 weeks had lower dry weight, comparable or greater number of leaves and stem length, when compared with their respective nonstored control groups after 2 weeks in the greenhouse. Seedlings stored for 4 weeks had lower number of leaves and stem length after 2 weeks in the greenhouse, except for those grafted onto the interspecific squash rootstock. Nongrafted and grafted watermelon seedlings with the same watermelon cultivar as rootstock showed significantly lower leaf net photosynthetic rates after 2 weeks in the greenhouse after the 2-week storage than those of nonstored control groups. In contrast, when grafted onto interspecific squash and bottle gourd rootstocks, seedlings showed comparable net photosynthetic rate to the control group. For all seedling types, 20% to 35% of seedlings died during 4-week storage or poststorage in the greenhouse, whereas all seedlings survived for the 2-week storage, except when grafted onto watermelon as rootstock. Therefore, chilling-tolerant rootstocks ‘Strong Tosa’ interspecific squash and ‘Emphasis’ bottle gourd improved storability of grafted ‘Tri-X-313’ watermelon seedlings but could not extend the storability beyond 2 weeks.

Industrial and systems engineering has been widely applied to analyze and optimize complex processes in various industries taking a highly computational approach. Plant factory-based production systems can utilize the same approach to effectively increase efficiency and reduce the cost of crop production under controlled environment. This chapter introduces our transdisciplinary work of integrating controlled environment crop production technologies, industrial and systems engineering, and agricultural economics using plant propagation nursery industries and their supply chain as a model case.

Intumescence injury is an abiotic-stress-induced physiological disorder associated with abnormal cell enlargement and cell division. The symptom includes blister- or callus-like growths on leaves, which occur on sensitive cultivars of tomato when they are grown under ultraviolet (UV)-deficit light environment, such as light-emitting diodes (LEDs). Previous studies suggest that intumescence can be reduced by increasing far-red (FR) or blue light. In the present study, effects of end-of-day FR (EOD-FR) light and high blue photon flux (PF) ratio during the photoperiod on intumescence injury were examined using ‘Beaufort’ interspecific tomato rootstock seedlings (Solanum lycopersicum × Solanum habrochaites), a cultivar highly susceptible to intumescence injury. Our study showed that EOD-FR light treatment moderately suppressed intumescence injury. Using EOD-FR light treatment, the percent number of leaves exhibiting intumescences was reduced from 62.0–70.7% to 39.4–43.1%. By combining high blue PF ratio (75%) during the photoperiod and EOD-FR light treatment, the percent number of leaves exhibiting intumescences was further suppressed to 5.0%. Furthermore, the combination of high blue PF ratio and EOD-FR light treatment inhibited undesirable stem elongation caused by EOD-FR light treatment. We found that high blue PF ratio during the photoperiod combined with a small dose of EOD-FR lighting (≈1 mmol·m−2·d−1 provided by 5.2 µmol·m−2·s−1 FR PF for 3.3 minutes) could inhibit the problematic intumescence injury of tomato plants grown under LEDs without negatively influencing growth or morphology.

Effects of end-of-day far-red (EOD-FR, 700-800 nm) light and high blue photon flux ratio during the photoperiod on intumescence injury were examined for 'Beaufort' and 'Maxifort' tomato rootstock seedlings (Solanum lycopersicum × Solanum habrochaites) grown with 13 mol m-2 d-1 daily light integral (199 µmol m-2 s-1 photosynthetic photon flux, 18 h photoperiod). The EOD-FR light treatment (1.1 mmol m-2 d-1 provided by 6.0 µmol m-2 s-1 FR photon flux for 3 min at EOD) significantly reduced intumescence injury. For example, by the EOD-FR light treatment, the incidences of leaf abscission were reduced from 88 to 8% for 'Beaufort' and from 79 to 25% for 'Maxifort'. However, EOD-FR light caused undesirable stem extension (41% greater than that without EOD-FR light). By combining relatively high B (blue, 400-500 nm) to R (red, 600-700 nm) photon flux ratio (50%B-50%R) during the photoperiod with EOD-FR light, intumescence injury was further decreased without causing undesirable stem extension. For example, the incidences of leaf abscission were reduced from 88 to 0% for 'Beaufort' and from 79 to 0% for 'Maxifort', compared to those under 10%B-90%R without EOD-FR light. Also, the percentages of leaves that exhibited intumescences were reduced from 68 to 30% for 'Beaufort' and from 55 to 19% for 'Maxifort'. Our study demonstrated that blue-rich light quality combined with a small dose of EOD-FR lighting could be applied to mitigate the problematic intumescence injury of tomato seedlings grown under LEDs.

of water, respectively. The air relative humidity for fog cooling was slightly higher than that for pad-and-fan cooling, at approximately 35%. An English version of Visual VETH (ventilation-evapotranspiration-temperature-humidity) software was also developed. A cooling strategy devised for semiarid greenhouses found that the air relative humidity inside a greenhouse decreased with an increase in ventilation rate as expected from simulation based on steady-state energy balance equations, while the water use for fog cooling increased. A simple and unique control algorithm for fogging and ventilation inlet openings demonstrated the possibility of maintaining relative humidity and air temperature simultaneously within a desirable range while reducing the water use for fog cooling. The tomato plant canopy transpiration rate and the water balance relative to the natural ventilation rate in a fog-cooled greenhouse were also investigated. The transpiration rate increased linearly with an increase in vapor pressure deficit (VPD) of the air. At a lower ventilation rate made possible by reducing the ventilation inlet openings, total water use in the greenhouse decreased by 13% and relative humidity increased as was expected from the steady-state energy balance simulation. The decrease in canopy transpiration resulted from the decrease in VPD, and was at a magnitude greater than that of the fog evaporation rate under similar experimental conditions with relatively high humidity in the range of 70-94%. By optimizing the natural ventilation rate, the greenhouse could be effectively cooled with less water use. Arizona can be considered a model analogous to many other semiarid climate conditions. Due to the long history of greenhouse technology development, the application of greenhouse crop production to an area with excessive radiation and dry air remains a relatively new effort. We believe that our efforts will contribute not only to the American Southwest but also to enhancing the application of greenhouse technology for crop production in these climate regions worldwide, including Mexico, China, the Middle East and Africa.

Light emitting diodes (LEDs) are frequently regarded as a new light source for the production of horticultural crops under closed-type conditions. However, before use of LEDs as the sole source of light can be advanced, plant responses to light quality have to be investigated for important horticultural plants. The objective of the present study was to evaluate cucumber (Cucumis sativus) seedlings physiological responses to different blue (B) and red (R) photon flux (PF) ratios using LEDs. Cucumber seedlings (cv. Cumlaude) were grown in a growth chamber until the second true leaf stage (17 days) with LED lighting and 18-h photoperiod. The treatments consisted of 100 μmol m−2 s−1 photosynthetic photon flux (PPF) with B:R PF ratios of 0B:100R%, 10B:90R%, 30B:70R%, 50B:50R%, 75B:25R%, 100B:0R%. Another treatment consisted of B, green (G) and R PF ratio of 20B:28G:52R%. Peak wavelengths of LEDs were 455 nm (B) and 661 nm (R) for the in the B:R treatments and 473 nm (B), 532 nm (G), 660 nm (R) in the B:G:R treatment. Hypocotyl length decreased with the increase of B PF up to the 75B:25R% treatment. Hypocotyl length in the 0B:100R% treatment was 164% greater than in the 75B:25R treatment. Plants under the 100B:0R% treatment had unexpected greater plant height, hypocotyl, and epicotyl length than plants under all other treatments. For example, the hypocotyl length under the 100B:0R% was 69% greater than in the 0B:100R treatment and 346% greater than in the 75B:25R% treatment. Leaf area decreased with the increase of B PF when plants were irradiated with the combination of B and R PF. The response of leaf area under the 100B:0R% treatment was unexpected since plants in the 100B:0R% treatment had 48% greater leaf area than plants in the 75B:25R% treatment. Chlorophyll content per leaf area, net photosynthetic rate, and stomatal conductance increased with the increase of B PF. Shoot dry and fresh mass decreased with the increase of B PF when plants were irradiated with the combination of B and R PF. Plants under 0B:100R% had the lowest dry and fresh mass from all the treatments and plants under 100B:0R% showed the greatest fresh mass from all the treatments and equal dry mass as the plants under 10B:90R% treatment. The addition of G PF to the spectrum did not have any influence in cucumber plant responses. For cucumber seedlings, morphological responses influenced plant growth since B PF responses in growth parameters (i.e., dry mass) closely matched those in morphological parameter (i.e., leaf area). More research is needed to find the optimal spectrum for the growth and development of horticultural crops under sole source electrical lighting such as LEDs.

To increase the available photosynthetic photon flux (PPF) for plant growth, greenhouse growers sometimes use electric lighting to supplement solar light. The conventional lighting technology used to increase PPF in the greenhouse is high-pressure sodium lamps (HPS). A potential alternative to HPS is high-intensity light-emitting diodes (LEDs). The objective of this study is to compare supplemental LED lighting with supplemental HPS lighting in terms of plant growth and morphology as well as discuss the energy use efficiencies of the fixtures. There were three light treatments: 1) blue LED (peak wavelength 443 nm); 2) red LED (peak wavelength 633 nm); and 3) HPS, to provide 3.7 ± 0.2 mol·m−2·d−1 (background solar radiation of 6.3 ± 0.9 mol·m−2·d−1). Cucumber (Cucumis sativus) plants at the transplanting stage (26 to 37 days) under HPS had 28% greater dry mass than did plants under the LED treatments. This can be attributed to the higher leaf temperature under the HPS treatment. No differences were observed in growth parameters (dry mass, fresh weight, or number of leaves) between the blue and red LED treatments. Plants under the blue LED treatment had greater net photosynthetic rate and stomatal conductance (gS) than those under the red LED and HPS treatments. Plants under the blue LED and HPS treatments had 46% and 61% greater hypocotyl length than those under the red LED, respectively. The fixture PPF efficiencies used in the experiment were 1.9, 1.7, and 1.64 μmol·J−1 for the blue LED, red LED, and HPS treatments, respectively; however, the fixture growing efficiency (g·kWh−1) of HPS was 6% and 17% greater than the blue LED and red LED treatment, respectively. In summary, supplemental red LED produced desirable plant compactness and HPS had greater fixture growing efficiency than LEDs.

This transdisciplinary study has a three-fold systems approach in evaluating a horticultural technology: 1) horticultural evaluations, 2) economic and resource analyses, and 3) systems engineering analyses, using low temperature storage as an example technology. Vegetable grafting is a technique to produce value-added seedlings but requires labor intensive nursery operations. Low temperature storage of seedlings for a short period of time can reduce peak production, but has not been evaluated at the extent demonstrated in this paper. Seedlings of 22 genotypes of Cucurbitaceae (cucurbit family) and Solanaceae (nightshade family) were evaluated for storability under selected temperatures and photosynthetic photon flux. Storability of Cucurbitaceous seedlings varied between 2 to 4 weeks at 12°C and 13 μmol m-2 s-1. Solanaceous seedlings were generally storable for 4 weeks at 12°C and 13 μmol m-2 s-1, but tomato seedlings could be stored for 4 weeks at 10°C and 5 μmol m-2 s-1. Capital and weekly operational costs of a low temperature storage system with a design that meets environmental requirements were estimated as $671 to $708 per m2 footprint and $0.79 to $2.21 per m2 footprint per week, respectively. Electricity costs per plant was less than 0.1 cents for 2 to 4 weeks of storage. Using a schedule-optimization heuristic and a logistics simulator previously developed for grafting nursery operations, six production scenarios consisting of two crops (tomato or watermelon) and three production peak patterns were examined to evaluate the impact of including low temperature storage. While the overall average costs of grafting labor were not significantly different, maximum labor demand and grafting labor cost during the peak production week were reduced by 31% to 50% and 14% to 30% by using storage, respectively. Therefore, low temperature storage can be an effective means to address the issue of labor management in grafting nurseries.

Grafting of fruiting vegetables is a relatively new advent in the United States with promise as a technology to improve both yields and the environment. However, investing in a commercial-sized grafting enterprise requires substantial capital investment and is a risky endeavor. A tool to help evaluate grafting costs for different production technologies and sizes of operation is a useful decision aid for individuals investing in new or modifying existing operations to produce grafted plants. Using a combination of engineering and financial equations, a scenario-based analysis was completed to obtain approximate capital and variable costs per plant for both new and existing production facilities. For exemplary purposes, four scenarios consisting of two different crops (tomato and watermelon) at two production sizes with different technology levels [low-volume manual grafting (one million plants per year) and high-volume fully automated grafting (100 million plants per year)] are presented to compare costs. For simplification purpose, consistent weekly production was assumed in the cost simulation. Total capital costs were $115,127 and $118,974 for low-volume production for grafted tomato and watermelon plants, respectively. They were $21.6 million and $16.7 million under high-volume production for tomato and watermelon, respectively. Among the four scenarios evaluated, variable costs per plant (costs of plants produced) were lowest for watermelons with high-volume production ($0.089 per plant), suggesting that production costs of grafted plants could decrease by scaling up production and introducing automation. Sensitivity analyses for high-volume production of tomato showed that the electricity rate, grafting clip price, and grafting robot speed were factors with the greatest influence on costs of plants. Scenario-based cost analysis was shown to be an effective tool for developing strategies to reduce the price of grafted plants.

High intensity light-emitting diodes (LEDs) have the potential to be used as supplemental lighting technology in greenhouses. However, LED light quality requirements of greenhouse crops grown when supplementing the solar spectrum are unknown. In this study, to find the requirements, cucumber ( Cucumis sativus L. cv. Cumlaude) seedlings were grown in a greenhouse with and without supplemental LED lighting (PPF: 54 ± 1.1 μmol m −2 s −1 ) at varied blue (400–500 nm with the peak at 455 nm) and red (600–700 nm with the peak at 661 nm) photon flux (PF) ratios (B:R ratios) under different solar daily light integrals (DLI). The treatments were 0B:100R% (54 μmol m −2 s −1 red PF), 4B:96R% (2.3 and 52 μmol m −2 s −1 blue and red PF, respectively), 16B:84R% (8.5 and 46.2 μmol m −2 s −1 blue and red PF, respectively), and a control without supplemental lighting. The solar DLIs during the experiment were 5.2 ± 1.2 and 16.2 ± 5.3 mol m −2 d −1 created inside a greenhouse using shade screen. Regardless of B:R ratio, morphological and growth parameters of the seedlings were all improved under supplemental LED lighting compared to the no-supplemental-light control. Under high DLI conditions, no significant differences were found for any parameters between the different B:R ratios. Under low DLI, chlorophyll concentration increased with increasing B:R ratio (i.e., increasing blue PF without increasing photosynthetic photon flux, PPF) of the supplemental lighting. Dry mass, leaf number, and leaf area decreased with increasing B:R ratio under low DLI conditions. The reduction in dry mass and leaf number were attributed to the reduction in leaf area. Leaf net photosynthetic rate measured under ambient CO 2 , ambient temperature, and 1000 μmol m −2 s −1 PPF (light source: tungsten halogen lamp) also showed no difference among treatments of B:R ratios, indicating that B:R ratio treatments did not cause any changes in plant photosynthetic apparatus. When used for supplemental lighting in the greenhouse, use of 100% red LED is preferred for cucumber seedlings, and additional blue LED was not beneficial.

For vegetable seedling propagators, integrating grafting technology into their propagation operations is critical to keeping or expanding market share in the near future. In this paper, an integrated discrete event simulation and Analytic Hierarchy Process (AHP) approach is proposed to help vegetable seedling propagators design grafting operation. The proposed approach consists of four steps: (1) defining performance criteria and factors (i.e. system alternative parameters and noise factors), (2) identifying significant factors via Design of Experiment (DOE), (3) evaluating system alternatives, and (4) AHP. For steps 2 and 3, a generic propagation simulator is developed with the focus on specific grafting operations (e.g. creating rootstocks, scions and grafted seedlings) while considering biological factors (e.g. seed disease and disease infection). Both classic and fuzzy AHP methods are adopted for addressing multiple criteria (e.g. variable cost, grafting throughput time, total capital expenses, resource utilization and percentage of order fulfilled in time with acceptable quality) of decisions. To address the imprecise ranking led by utilizing sample means of alternative performance data in pairwise comparison, a Best Alternative Search (BAS) procedure is proposed for AHP by considering bounds of confidence intervals in ranking alternatives. In the experiments, six system alternatives involving three automation levels (e.g. manual, semi- and fully-automated grafting) and eight scenarios are applied to a large-scale seedling propagator located in North America. Results demonstrate that (1) classic AHP produces the similar trend as fuzzy AHP, (2) the proposed BAS procedure can ensure the ranking accuracy of AHP, and (3) the proposed approach can be successfully used by vegetable seedling propagators to support the design of a grafting operation.

Optimal facility layout planning is needed for building or retrofitting production facilities (industrial or agricultural) in order to maximize production capacity and efficiency. In labor-intensive agricultural plant production facilities, this process is especially complicated due to the uncertainties surrounding the dynamicity of workers’ performance and plant growth affected by climate conditions. In this work, a simulation-based optimization framework is developed to simultaneously find the optimal facility layout design and resource allocation applicable for vegetable grafting nurseries that involve highly labor-intensive young plant production with multiple operational stages. In particular, optimal layout algorithms are embedded within the simulation model in order to find an optimal layout design given available resources. The proposed model can be customized based on workers’ individual performance and managerial design preferences. When applied to a case study of designing a new greenhouse nursery, results reveal that our proposed framework can lead to a potential daily savings of 20.64% or $1421.44 on average in terms of labor, utility, and amortized costs.

A control strategy for greenhouse cooling with natural ventilation and variable high-pressure fog was evaluated via computer simulation and verified experimentally. Two set points were used, one based on air specific enthalpy (56 kJ kg-1) for determining the vent openings, and the other based on vapor pressure deficit (VPD) of the air (1.0 kPa) for controlling the fogging rate. These set points would maintain the greenhouse air at a temperature of 24°C and a relative humidity of 67%. Achieving the VPD set point was the priority, and excessive air exchange was avoided through adjustments of the vent openings when fogging demands were beyond the operational capacity of the fogging system. Results of simulations and experiments from four different days (18, 19, 29 June and 3 July 2011) were in good agreement. The performance of the control strategy developed was satisfactory to maintain the greenhouse indoor climate close to the set points with 1.1 ±0.4 kPa and 26°C ±1.7°C for inside air VPD and temperature, respectively (with relative humidity of 67% ±8%). The implementation results demonstrated that the control strategy was capable of reducing the air VPD by an average of 4.2 kPa when the average outside air VPD was 5.4 kPa and reducing the air temperature by an average of 10.5°C when the average outdoor air temperature was 37°C, and the greenhouse relative humidity was increased by an average of 52% compared to outside during the four experiment days. Deviations between the simulated and measured variables inside the greenhouse were attributed to a prevailing high and variable-magnitude outside wind speed during the experiments as well as to the time delay on the retrieval of climate data needed for computations of the strategy. Real-time climate parameters with no delay are preferable for effective computations of ventilation rates and desired fogging rates. The strategy that was developed in this study maintained the VPD close to the selected set point for all the experimental periods evaluated. Finally, the control strategy developed effectively maintained desirable climate conditions inside the greenhouse, and the simulation results were experimentally validated.

Lamp spectral customization can be a strategy to achieve desirable plant characteristics when plants are grown under sole-source electric lighting. Vegetable transplants can be efficiently and economically grown under indoor-production systems with electrical lighting; however, species-specific light recipes have to be developed to improve plant growth, development and morphology, as well as to reduce electrical consumption. The objective of this study was to evaluate the growth and morphology of tomato transplants to a broad range of blue to red (B:R) photon flux (PF) ratios under LEDs and cool white fluorescent lamps (CWF). Tomato 'Komeett' and 'Beaufort' seedlings were grown in a climate control growth chamber. Using LEDs, seven light treatments with different blue (B), green (G) and red (R) PF ratios were used: 100R, 10B:90R, 20B:28G:52R, 30B:70R, 50B:50R, 75B:25R and 100B. In addition, a CWF treatment served as the control. Hypocotyl length of 'Komeett' decreased with the increase of percent B PF up to 75% B. Plant leaf area was 64-72% greater under treatments emitting both B and R PF than in the 100 B and 100 R treatments. Similarly, tomato 'Komeett' fresh mass, dry mass, leaf number and chlorophyll concentration was comparable among the treatments containing B and R PF and greater than in 100 B and 100 R treatments. However, plant compactness in the 30B:70R treatment was 42% greater than in the 10B:90R treatment. Anthocyanin concentration increased with the increase of percent B PF up to 75% B. Also, plants in 30B:70R and 50B:50R had 39% and 36% greater dry mass than in CWF, respectively. In addition, 30B:70R and 50B:50R LEDs had 172% greater growing efficacy (g kWh(-1)) than high output fluorescent lamps. The addition of G light did not have any effects on tomato physiological responses. `Beaufort' plant morphology and growth were severely affected by intumescences development and intumescence severity decreased under higher percentages of B PF. In summary, 30B:70R, 50B:50R were the best spectrums to produce tomato seedlings under LEDs tested here; however, plant quality under CWF, 10B:90R, 20B:28G:52R, and 75B:25R was also acceptable. Published by Elsevier B.V. USDA NIFA SCRI grant [2010-51181-21369] The authors would like to acknowledge Mark Kroggel and Neal Barto at the University of Arizona (CEAC) for their technical advice. This project was funded by USDA NIFA SCRI grant No: 2010-51181-21369.