Daily Light Integral Research Articles

Productivity, photosynthetic light-use efficiency, nitrogen metabolism and nutritional quality of C4 halophyte Portulaca oleracea L. grown indoors under different light intensities and durations.

Portulaca oleracea L. (known as purslane), is a nutritious facultative C4 halophyte. Recently, it has been successfully grown indoors under LED lightings by our team. However, basic understanding about the impacts of light on purslanes are lacking. This study aimed to investigate the effects of light intensity and duration on productivity, photosynthetic light use efficiency, nitrogen metabolism and nutritional quality of indoor grown purslanes. All plants were grown in 10% artificial seawater hydroponically under different photosynthetic photon flux densities (PPFDs) and durations and thus different daily light integrals (DLI). They are, L1 (240 µmol photon m-2 s-1, 12h, DLI = 10.368mol m-2 day-1); L2 (320 µmol photon m-2 s-1, 18h, DLI = 20.736mol m-2 day-1); L3 (240 µmol photon m-2 s-1, 24h, DLI = 20.736mol m-2 day-1); L4 (480 µmol photon m-2 s-1, 12h, DLI = 20.736mol m-2 day-1), respectively. Compared to L1, higher DLI promoted root and shoot growth and thus increased shoot productivity by 2.63-,1.96-, 3.83-folds, respectively for purslane grown under L2, L3, L4. However, under the same DLI, L3 plants (continuous light, CL) had significantly lower shoot and root productivities compared those with higher PPFDs but shorter durations (L2 and L4). While all plants had similar total chlorophyll and carotenoid concentrations, CL (L3) plants had significantly lower light use efficiency (Fv/Fm ratio), electron transport rate, effective quantum yield of PSII, photochemical- and non-photochemical quenching. Compared to L1, higher DLI with higher PPFDs (L2 and L4) increased leaf maximum nitrate reductase activity while longer durations increased leaf concentrations and total reduced nitrogen. There were no significant differences in leaf total soluble protein, total soluble sugar and total ascorbic acid concentrations in both leaf and stem regardless of light conditions. However, L2 plants had the highest leaf proline concentration but leaf total phenolic compounds concentration was higher in L3 plants instead. Generally, L2 plants had the highest dietary minerals such as K, Ca, Mg and Fe among the four different light conditions. Overall, L2 condition is the most suitable lighting strategy in enhancing productivity and nutritional quality of purslane.

Prediction Model of Pumpkin Rootstock Seedlings Based on Temperature and Light Responses

Temperature and light are the key factors that affect the quality of pumpkin rootstock seedlings’ growth process. Responses to temperature and light are an important basis for optimizing the greenhouse environment. In order to determine the quantitative effects of temperature and light on the growth and development of pumpkin (Cucurbita moschata cv. RTWM6018) rootstock seedlings, relationships between temperature, light, and pumpkin rootstock seedlings growth were established using regression analysis. The results indicated that the daily average temperature had a significant negative correlation with the development time of pumpkin rootstock seedlings, and the shoot dry weight of pumpkin rootstock seedlings increased within a certain range of the daily light integral (DLI). We established a prediction model of pumpkin rootstock seedling quality indicators (hypocotyl length, stem diameter, shoot dry weight, root dry weight, root shoot ratio, and seedling quality index) based on thermal effectiveness and photosynthetic photon flux density (TEP). The coefficient of determinations (R2) of the hypocotyl length and seedling quality index prediction models of pumpkin rootstock seedlings, based on accumulated TEP, were 0.707 and 0.834, respectively. The hypocotyl length and seedling quality index prediction models of pumpkin rootstock seedlings, based on accumulated TEP, were y1 = 0.001 x2 − 0.180 x + 13.057 and y2 = 0.008 x0.722, respectively, which could be used for predicting the growth of pumpkin rootstock seedlings grown under different temperature and light conditions.

Evaluation of the impact of photoperiod and light intensity on decreasing days to maturity in winter wheat

AbstractThe development and improvement of crop cultivars are necessary to meet the demands of the growing global population. The ability to decrease the generation time is imperative for breeders to achieve higher rates of genetic gain annually. Understanding the way in which photoperiod affects the maturation rate of these crops, including winter wheat (Triticum aestivum L.), is required for decreasing generation time in breeding programs. The effects of prolonged photoperiod and light intensity on winter wheat generation time were studied to determine if photoperiod may contribute to a shortened cycle time. Three winter wheat cultivars (Branson, CFBA1401, and Norstar) and one spring wheat cultivar (AC Carberry) were exposed to four treatments based on the daily light integral (DLI): high light (HL) or low light and photoperiod as follows: 22 h of light and 2 h of dark (22:2) or 16 h of light and 8 h of dark (16:8). Generation time, as measured by days to maturity in the HL22:2 treatment, resulted in a decrease of 8 days or 7% of the total generation time, compared to the control, HL16:8 treatment. Photoperiod itself had a minimal effect on generation time when both DLI and temperature were controlled. An improved understanding of the effects of photoperiod, thermal time, and DLI and their interactions is required prior to implementation in a winter cereal breeding program.

Designing plant–transparent agrivoltaics

Covering greenhouses and agricultural fields with photovoltaics has the potential to create multipurpose agricultural systems that generate revenue through conventional crop production as well as sustainable electrical energy. In this work, we evaluate the effects of wavelength-selective cutoffs of visible and near-infrared (biologically active) radiation using transparent photovoltaic (TPV) absorbers on the growth of three diverse, representative, and economically important crops: petunia, basil, and tomato. Despite the differences in TPV harvester absorption spectra, photon transmission of photosynthetically active radiation (PAR; 400–700 nm) is the most dominant predictor of crop yield and quality. This indicates that different wavebands of blue, red, and green are essentially equally important to these plants. When the average photosynthetic daily light integral is > 12 mol m–2 d–1, basil and petunia yield and quality is acceptable for commercial production. However, even modest decreases in TPV transmission of PAR reduces tomato growth and fruit yield. These results identify crop-specific design requirements that exist for TPV harvester transmission and the necessity to maximize transmission of PAR to create the most broadly applicable TPV greenhouse harvesters for diverse crops and geographic locations. We determine that the deployment of 10% power conversion efficiency (PCE) plant-optimized TPVs over approximately 10% of total agricultural and pasture land in the U.S. would generate 7 TW, nearly double the entire energy demand of the U.S.

Optimization of an Indoor DWC Hydroponic Lettuce Production System to Generate a Low N and P Content Wastewater

Hydroponic production raises economic and environmental issues related to the treatment, recovery or disposal of hydroponic wastewater, which can be rich in eutrophication-related nutrients, nitrogen (N) and phosphorus (P). Little focus has been put on the influence of the growth conditions on the N and P content in hydroponic wastewater, which is of uttermost importance when it is intended to reuse the wastewater for irrigation or other purposes with reduced impact on the environment. This study aimed to optimize an indoor non-recirculating deep-water culture (DWC) hydroponic system for lettuce (Lactuca sativa L. var. crispa) production, in terms of daily light integral (DLI) and volume of nutrient solution (NS) per plant, to maximize both the biomass production and the N and P removal, allowing for the wastewater to meet the criteria established for reusing in irrigation and minimizing the eutrophication impacts. A small-scale DWC hydroponic system with a fluorescent light fixture was built to study lettuce growth indoors for 35 days after transplanting (DAT). A first experiment was conducted under 14, 20 or 23 mol m−2 d−1 DLI and with 1.5 or 2 L of NS per plant. A pronounced inner leaf tip burn was observed, regardless of the volume of NS solution used, related to the unventilated conditions under high radiation. Total biomass was similar in all treatments and N and P removal was higher than 95% and 94%, respectively, at 35 DAT. Lettuces grown in 2 L of NS per plant exhibited higher average biomass. A second experiment was performed under 8, 10 or 12 mol m−2 d−1 DLI and with 2 or 3 L of NS per plant, making it possible to achieve healthy biomass at 35 DAT with higher water and light-use efficiency when compared to the first experiment. A DLI of 10 or 12 mol m−2 d−1 with 2 L of NS per plant and a DLI of 12 mol m−2 d−1 with 3 L of NS per plant made it possible to achieve both the best total biomass production and the highest N and P removal from water. Under those conditions, hydroponic wastewater complied with N and P criteria for reuse in irrigation, showing potential to be used as an alternative resource for agriculture and to minimize negative impacts on the environment.

Supplemental lighting spectrum impact on sweet potato cutting production and rooting

AbstractLight is an important factor in plant growth and morphology of sweet potato (Ipomoea batatas L. Lam). This study explored the impact of supplemental lighting provided by three commercially available units on a stock plant cutting production and cutting rooting of two sweet potato cultivars ‘Covington’ and ‘Beauregard’. In experiment one, stock plants were grown under one of four lighting conditions, no supplemental light, high blue light emitting diode (LED), low blue LED, or halogen. Cuttings were collected twice a week for 5 wk and the total weekly cutting number and cutting caliper per plant were recorded. During this experiment plants grown under supplemental lighting exhibited significantly greater weekly total cutting numbers after 2 wk of growth when compared with those that were not exposed to supplemental lighting. In experiment two, cuttings were rooted under the same four light treatments and sampled on Days 7, 14, and 21 in which the cutting height, root weight, and shoot weight were recorded. On Day 21 Covington plants grown under low blue and halogen supplemental lighting exhibited significantly greater root dry weight when compared with those that did not receive supplemental lighting. However, no differences in rooting were observed for Beauregard. These results demonstrate that supplemental light increases stock plant growth regardless of the three commercially available light spectrums examined when compared with no supplemental light. This suggests that increasing the daily light integral (DLI) has a larger impact on plant growth than the spectrum of the commercially available lights that were examined.

GREENBOX Technology II - Comparison of Environmental Conditions, Productivity, and Water Consumption With Greenhouse Operation

Highlights Increasing population, demand, and urbanization have increased food security pressures. We compared GREENBOX with a greenhouse for urban crop production. GREENBOX and greenhouse provided the required environmental conditions and comparable biomass output year-round. GREENBOX performance is comparable to a greenhouse for urban crop production but with more advantages. Abstract. The Yang Laboratory at the University of Connecticut has developed the GREENBOX technology for growing fresh produce in urban areas to meet the increasing demand for sustainable and local food production. Previous studies have shown that GREENBOX units can provide the desired environmental conditions to sustain crop production in midlatitude urban warehouse environments. This study was conducted to compare the environmental conditions, productivity, and water consumption for growing lettuce between GREENBOX and a conventional greenhouse that has been widely applied for crop production. Two modular GREENBOX units, equipped with LED lighting, hydroponic growing platform, and climate controls, were located in a high ceiling headhouse of a greenhouse complex to mimic warehouse conditions. We used bays in a nearby greenhouse that was glass glazed, equipped with supplemental lighting, and fully controlled by an Argus Titan control system for comparison purposes. Forty-eight (48) heads of Butterhead Rex lettuce (Lactuca sativa) were grown over four 30-day cycles in spring, summer, fall, and winter in the GREENBOX units and the greenhouse bays, respectively, at the University of Connecticut, Storrs, Connecticut, United States. Environmental variables, including light, temperature, relative humidity, and carbon dioxide concentration, were measured at a frequency of every minute. Biomass data of wet weight, dry weight, total leaf area, and lettuce head area were collected using destructive and non-destructive methods every three days. The water consumption rate was logged using a lysimeter. We derived the Daily Light Integral (DLI), Leaf Area Index (LAI), Specific Leaf Area (SLA), productivity, and water consumed per lettuce head, per unit wet weight, and per unit dry weight from the measurements. Results were analyzed using descriptive statistics and ANOVA. The DLI values in the GREENBOX units were significantly higher than the recommended minimum DLI by over 20 mol/m2.d in the GREENBOX units and over 10 mol/m2.d in the greenhouse bays. The range of the daily temperature variation is only a few degrees in the GREENBOX units, while in the greenhouse bays was over 20°C. The average daily temperature in both growing locations fell within the optimal range of 17-29°C for lettuce. The relative humidity inside both growing locations fell primarily within the optimal range of 40%-60%. The mean CO2 concentrations inside both growing locations were slightly lower than the ambient concentration of 350 ppm. Measured parameters such as LAI, SLA, and productivity followed similar patterns, slightly different amongst seasons and higher in warmer seasons. ANOVA revealed a slightly (statistically insignificant) higher level of productivity in the GREENBOX units over the greenhouse bays (p=0.16), with higher values during the warmer seasons (p=0.72 in spring and summer). GREENBOX used 1.83-2.69 L of water per lettuce head, while the greenhouse bays used 1.69-3.84 L of water per lettuce head year-round. The water use was consistently lower in the GREENBOX units. We found that the GREENBOX units and greenhouse bays provided comparable environmental conditions, biomass output, and water consumption. Those variables, however, were more consistent in the GREENBOX units. GREENBOX environment was less affected by outside weather and, therefore, exhibited reduced fluctuations. The GREENBOX is advantageous over the greenhouse as it does not require arable or open land for intercepting sunlight and can be operated in available urban buildings such as warehouses. Keywords: GREENBOX, Greenhouse, Lettuce, Productivity, Water use.

GREENBOX Technology I - Technical Feasibility and Performance in Warehouse Environment

Highlights There are pressures on food security due to increasing population, demand, and urbanization. GREENBOX uses controlled environment agriculture for urban crop production in warehouse settings. GREENBOX provided the required environmental conditions and comparable biomass output year-round. GREENBOX is technically feasible for urban crop production. Abstract. The surging worldwide population and urbanization have increased food security and safety pressures. Therefore, there is a need to increase food production capacity in urban areas to feed this growing population. We have developed the GREENBOX technology to grow vegetables in individual climate-controlled boxes in urban warehouse environments. A GREENBOX is a thermally insulated modular structure of standard size with an artificial lighting source, a hydroponic nutrient supply system, and environmental controls. GREENBOX units can be used together in various numbers to form different configurations and production capacities. This study was conducted to evaluate the technical feasibility and performance of the GREENBOX technology for urban crop production in warehouse settings commonly found in urban areas. Two model GREENBOX units, constructed with commercially available parts, were located in a high-ceiling headhouse of a laboratory greenhouse complex at Storrs, Connecticut, USA, for the study. Forty-eight (48) heads of Butterhead Rex lettuce (Lactuca sativa) were grown in the model GREENBOX units (24 in each) over a 30-day growing cycle for four seasons. Environmental data, including light, temperature, relative humidity, and carbon dioxide, were collected using iPonic sensors at a frequency of every minute and processed to 15-minute averages. Crop growth was quantified with biomass data, which were wet weight, dry weight, total leaf area, and lettuce head area, using destructive and non-destructive methods every three days. A lysimeter was used to determine the water consumption rate by plants every fifteen minutes. We derived the Daily Light Integral (DLI), Leaf Area Index (LAI), Specific Leaf Area (SLA), productivity, and water consumed per lettuce head, per unit wet weight, and per unit dry weight. Descriptive statistics were used to describe and analyze the results. The DLI in the GREENBOX ranged between 32.48-37.23 mol/m2.d at the lettuce heads' height, higher than the recommended minimum DLI of 6.5-9.7 mol/m2.d. GREENBOX does not rely on external light but solely on the artificial lighting source, regulated at the grower's discretion. The mean temperatures inside were 24.5-26.9°C, falling within the optimal range of 17-29°C for lettuce. The artificial lighting source was a heat source to sustain cultivation. All year, the average relative humidity was 35.53%-58.54%, mostly within the ideal range of 40%-60%. The CO2 concentration inside the boxes fell slightly below the ambient concentration of 350 ppm, between 301.39 and 311.34 ppm over different seasons. Measured growth parameters, including LAI (5.3-6.5 cm2/cm2), SLA (344.3-569.3 cm2/g), and productivity (6.33-7.38 kg/m2), all followed similar patterns, slightly different amongst seasons and higher in warmer seasons. GREENBOX used 1.83-2.69 liters of water per head of lettuce consistently year-round, 95% lower than soil-based irrigation. Lettuce plants were healthy and grew to full size in the 30-day cycle, regardless of the season. Our study showed that the GREENBOX technology was capable of providing desired environmental conditions for growing lettuce crops all year around in the experimental warehouse structure and consequently having a high potential to be applied in food production in mid-latitude urban settings. Keywords: Agricultural facility, Environmental control, GREENBOX, Lettuce, Urban agriculture.

An Energy-Efficient PAR-Based Horticultural Lighting System for Greenhouse Cultivation of Lettuce

This paper presents an intelligent horticulture lighting and monitoring system to achieve energy-efficient supplemental lighting while maintaining the light quality and intensity at desired levels in the photosynthesis spectrum. Energy-efficiency is achieved through delivering only the required net light intensity, consisting of sunlight and supplemental LED light, using an intelligent controller that does not depend on the lighting system model. To this end, an online neural-network learning control system is developed, comprised of low-cost light sensors for measuring the photosynthetic photon flux density (PPFD), dimmable LED light fixtures, cameras, and internet-of-things (IoT)-enabled firmware used for crop monitoring and performance evaluation. Experiments performed in a research greenhouse facility on the lettuce crop are presented which indicate that the system can deliver the desired Daily Light Integrals (DLIs) to the plants in the presence of changing daylight conditions. The proposed method can thus deliver the exact amount of light to a specific crop based on the required light recipes during different growth phases. The control performance is further compared with a conventional on-off time-scheduling method in terms of plant health, growth, and energy requirements. The experiments indicate that the proposed solution can reduce energy consumption per unit dry mass of lettuce by 28% when compared to existing time-scheduling methods.

Effects of Environmental Changes by an Agrivoltaic System on Growth and Quality Characteristics of Kimchi Cabbage

Background and objective: For a successful application of agrivoltaic (AV) system, decrease in crop productivity must be minimized while achieving power generation. In this study, changes in microenvironments, crop growth and quality under the AV panels were investigated for kimchi cabbage.Methods: On September 1, 2021, kimchi cabbage (<i>Brassica rapa</i> ssp. <i>pekinensis</i>) 'Bulam No. 3' was planted in the soil under the AV panels and in an open field for the control, and grown using a conventional method. Growth characteristics and internal components after 16 weeks were analyzed.Results: There was no difference in air temperature and relative humidity, however daily light integral (DLI) and soil temperature under the AV panels were lower than the control. Under the AV panels, plant width was lesser and plant height and head height were greater than the control. Head shape index and leaf number of the AV panel plot were greater than in the control. Trimming loss rate was lower but chlorophyll content was higher in the AV panel plot. Head hardness was lower in the AV panel plot, while head fresh weight was greater but head dry weight was smaller in the AV panel plot: therefore, moisture content was greater than the control. Marketable crop yield and heading rate was higher in the AV panel plot.Conclusion: The environmental changes caused by AV panels including the DLI and soil temperature induced a larger fresh weight, higher heading and trimming loss rates because a relatively good environment was created in the early crop stage which was the period of high temperature and DLI. However, the lower DLI of the latter period had a rather negative effect, resulting in an elongated shape, smaller dry weight, and shorter shelf life.

Photosynthetic Daily Light Integral Influences Growth, Morphology, Physiology, and Quality of Swordfern Cultivars

Boston and Australian swordferns (Nephrolepis sp.) are popular tropical ferns for hanging baskets and containers; however, greenhouse production occurs during times of the year when growers may need to deploy shade or supplemental lighting to manage the growing environment. Our objectives were to quantify the impact of the daily light integral (DLI) on growth, morphology, physiology, and ornamental quality of containerized Nephrolepis species and cultivars, and to establish optimal DLIs for containerized swordferns to assist commercial greenhouse growers with light management strategies during production. Eleven cultivars of Boston swordfern [N. exaltata (L.) Schott Blue Bells, Compacta, Fluffy Ruffles, Gold, Montana, Nevada, Petticoat, Pom Pom, Super, Tiger, and True] and one cultivar of Australian swordfern [N. obliterata (R. Br.) J. Sm. Western Queen] were investigated. Plants were grown for 58 days at 20 °C and placed under one of four different fixed-woven shadecloths providing ≈86%, 62%, 42%, or 26% shade or no shade, thereby establishing mean DLIs of 3.2, 6.4, 10.7, 12.4, and 17.1 mol⋅m−2⋅d−1, respectively. For most cultivars, the growth index, which is an integrated measurement of height and diameter, decreased linearly as the DLI increased from 3.2 to 17.2 mol⋅m−2⋅d−1, resulting in smaller compact plants. Increasing the DLI significantly affected the frond number of each cultivar differently, whereas dry mass generally increased as the DLI increased from 3.2 to 10.7 to 12.4 mol⋅m−2⋅d−1 for most cultivars. For each cultivar, as the DLI increased from 3.2 to 17.1 mol⋅m−2⋅d−1, the chlorophyll concentration index decreased, whereas the hue angle increased and chroma was unaffected. Our results indicate that growers should maintain ≈10 to 12 mol⋅m−2⋅d−1 during greenhouse Nephrolepis production; however, DLIs ≥5.5 mol⋅m−2⋅d−1 and ≤16.5 mol⋅m−2⋅d−1 also improved the quality of some Nephrolepis cultivars.

The extended day length promotes earlier flowering of bermudagrass.

Day length is a very critical environmental factor affecting plant growth and development. The extension of light application time has been shown to promote flowering in the long-day plant and to shorten breeding time in some crops. However, previous research on the regulation of bermudagrass flowering by light application time is scarce. Therefore, this study investigated the effect of day length on the growth and flowering of bermudagrass by prolonging the light application time in a controlled greenhouse. Three different light application times were set up in the experiment: 22/2 h (22 hours light/2 hours dark), 18/6 h (18 hours light/6 hours dark), 14/10 h (14 hours light/10 hours dark). Results showed that extending the light application time not only promoted the growth of bermudagrass (plant height, fresh weight, dry weight) but also its nutrient uptake (nitrogen (N) and phosphorous (P) content). In addition, daily light integrals were different when flowering under different light application times. Most importantly, under the 22/2 h condition, flowering time was successfully reduced to 44 days for common bermudagrass (Cynodon dactylon [L.] pers) genotype A12359 and 36 days for African bermudagrass (Cynodon transvaalensis Burtt-Davy) genotype ABD11. This study demonstrated a successful method of bermudagrass flowering earlier than usual time by manipulating light application time which may provide useful insights for bermudagrass breeding.

Air temperature during cutting propagation of cold-intermediate and -sensitive crops can be reduced if root-zone heating is provided

Asexual propagation of herbaceous ornamentals occurs from late winter to early spring coincides with seasonally low daily light integrals (DLIs) and average daily temperatures (ADT) outdoors. Supplemental lighting and air and root-zone heating (RZH) can be used to promote rapid callus induction and rooting of cuttings. Due to the range of greenhouse crop base temperatures (cold-tolerant, cold-intermediate, and cold-sensitive), one strategy is to reduce the air ADT of certain crops while using RZH as a potential energy saving strategy. Therefore, the objective of this study was to quantify how reduced air ADT and increased RZH temperatures influence root initiation and development of cold-intermediate and-sensitive herbaceous annual and perennial crops propagated by shoot-tip cuttings. Unrooted vegetative cuttings of angelonia ‘Archangel Raspberry’ (Angelonia angustifolia), lantana ‘Landmark Sunrise Rose Improved’ (Lantana camara), New Guinea impatiens ‘Clockwork White Improved’ (Impatiens hawkeri), scaevola ‘Scalora Brilliant’ (Scaevola aemula), thunbergia ‘Sunny Lemon Star’ (Thunbergia alata), verbena ‘Cadet Upright Red’ (Verbena × hybrida), geranium ‘Moxie! Deep Rose’ (Pelargonium interspecific), Kwik Kombos ‘Pink Lemonade Mix’ [petunia ‘Dekko Star Rose’ (Petunia × hybrida), lobelia ‘Techno Heat Light Blue Improved’ (Lobelia erinus), and calibrachoa ‘Callie Yellow Improved’ (Calibrachoa × hybrida)] and portulaca ‘Cupcake Carrot’ and ‘Colorblast Lemon Twist’ (Portulaca grandiflora) were inserted into a soilless medium and placed in a greenhouse with an air ADT of 21°C and RZH set point of 24°C to callus. After 6 d, trays of cuttings were placed between two greenhouses with an air ADT of 16 or 21°C and among 3 benches which provided RZH set points of 21, 24, or 27°C. After 14 or 16 d post-callus, measurements were collected for all genera and geranium and portulaca ‘Colorblast Lemon Twist’ were transplanted into a common environment. The air ADT and RZH individually influenced stem length of angelonia, lantana, kwik kombos, portulaca, thunbergia, and verbena, and interacted to influence angelonia and lantana. Under an air ADT of 21°C, angelonia was 30%-45% taller than an air ADT of 16°C. Stem length of geranium, New Guinea impatiens, and scaevola were not influenced by air ADT or RZH. With an RZH set point of 21°C, the root dry mass of thunbergia was 72% greater under an air ADT of 21 than 16°C. Lantana shoot dry mass was 23% smaller under an air ADT of 16°C and RZH of 21°C compared to an RZH of 24°C. Finished plants of geranium and portulaca were not influenced by air ADT or RZH and were comparable in size and date of marketability between treatments. Due to little to no differences in crop timing or quality, the majority of the crops studied can be propagated with an air ADT and RZH of 16 and 24°C, respectively, without negative effects during or after propagation.

A Model for Accurate Determination of Environmental Parameters in Indoor Zoological and Botanical Gardens Supporting Efficient Species Management

The detailed evaluation of environmental parameters can be a great tool for the optimal selection and location of vegetable species, not only in vegetable production facilities and greenhouses but also in zoological and botanical gardens, which frequently maintain delicate and exotic plant species with strict environmental requirements in immersive exhibits where conditions can vary remarkably. This study, developed at an indoor zoological garden (Biodomo—Parque de las Ciencias de Granada, Spain), evaluates a sampling protocol for the determination of seven environmental parameters: daily light integral (DLI) was determined at nine different locations of the facility using a portable Light Quantum SQ-500 sensor; air temperature, atmospheric pressure, and air relative humidity were measured using a fixed ATMOS14 sensor; and soil temperature, soil water content, and soil conductivity were determined using a fixed TEROS12 sensor. Values recorded for DLI showed statistically significant variations across the nine different sampling locations, as well as between the different months in all sampling spots. Significant variations were also detected across the 12 months of study for the rest of environmental parameters evaluated, and correlations were found between the studied parameters, with the correlation between soil and air temperature the strongest (rs = 0.758) and soil temperature significantly superior to air temperature. The methodology described in this study can be easily reproduced in similar indoor zoological and botanical facilities, increasing the knowledge of the environmental conditions, and allowing corrections that could improve species selection, location, and management.

Luminescent quantum dot films improve light use efficiency and crop quality in greenhouse horticulture.

The spectral quality of sunlight reaching plants remains a path for optimization in greenhouse cultivation. Quantum dots represent a novel, emission-tunable luminescent material for optimizing the sunlight spectrum in greenhouses with minimal intensity loss, ultimately enabling improved light use efficiency of plant growth without requiring electricity. In this study, greenhouse films containing CuInS2/ZnS quantum dots were utilized to absorb and convert ultraviolet and blue photons from sunlight to a photoluminescent emission centered at 600nm. To analyze the effects of the quantum dot film spectrum on plant production, a 25-week tomato trial was conducted in Dutch glass greenhouses. Plants under the quantum dot film experienced a 14% reduction in overall daily light integral, resulting from perpendicular photosynthetically active radiation transmission of 85.3%, mainly due to reflection losses. Despite this reduction in intensity, the modified sunlight spectrum and light diffusion provided by the quantum dot film gave rise to 5.7% improved saleable production yield, nearly identical total fruiting biomass production, 23% higher light use efficiency (g/mol), 10% faster vegetative growth rate, and 36% reduced tomato waste compared to the control, which had no additional films. Based on this result, materials incorporating quantum dots show promise in enabling passive, electricity-free spectrum modification for improving crop production in greenhouse cultivation, but extensive controlled crop studies are needed to further validate their effectiveness.

Predicting greenhouse daily light integral using photosynthetic photon flux density and finite difference method

In the state-of-the-art agricultural technology using greenhouses, it is useful to estimate a dynamic model of internal environmental changes according to external environmental changes. In this article, we propose a method to predict the change in the daily light integral inside the greenhouse according to the change in the daily light integral outside the greenhouse. Since daily light integral corresponds to the integral value of photosynthetic photon flux density, it is necessary to obtain a model of change in photosynthetic photon flux density inside the greenhouse according to the change in photosynthetic photon flux density outside the greenhouse to improve the prediction accuracy. The greenhouse was considered a nonlinear first-order system with a time lag for the photosynthetic photon flux density, and the system parameters were identified using the recursive least-squares method. Here, the photosynthetic photon flux density data measured outside the greenhouse is used as the input to the system, and the photosynthetic photon flux density data measured inside the greenhouse is used as the output of the system. Next, we obtain the daily light integral prediction model. The daily light integral prediction model is estimated from the photosynthetic photon flux density model using the finite difference method. The performance of the proposed method has been evaluated through extensive experimental studies. In Korea, since the weather changes in summer and winter are great, it must compare the daily light integral prediction performance in summer and winter to more accurately verify the proposed method. In this study, the experimental results are presented, respectively, for summer in August 2021 and winter in January 2022. The error performance of the human empirical prediction method and the proposed data-driven prediction method are compared for two seasons, and the robustness of the rapid weather changes of the proposed method is discussed.

Morphological and Physiological Traits of Greenhouse-Grown Tomato Seedlings as Influenced by Supplemental White Plus Red versus Red Plus Blue LEDs

The relatively low light intensity during autumn–winter or early spring and inclement weather such as rain or fog may lead to extended production periods and decreased quality of greenhouse-grown tomato seedlings. To produce high-quality tomato seedlings rapidly, the influences of supplementary lights with different spectra on the morphological and physiological traits of tomato seedlings were measured in a greenhouse. Supplemental lighting with the same daily light integrals (DLI) of 3.6 mol m−2d−1 was provided by white (W) light-emitting diodes (LEDs), white plus red (WR) LEDs, and red plus blue (RB) LEDs, respectively, and tomato seedlings grown under only sunlight irradiation were regarded as the control. Our results demonstrate that raised DLI by supplementary light improved the growth and development of greenhouse-grown tomato seedlings, regardless of the spectral composition. Under conditions with the equal DLI, the tomato seedlings grown under supplementary WR LEDs with a red to blue light ratio (R:B ratio) of 1.3 obtained the highest values of the shoot and root fresh weights, net photosynthetic rate, and total chlorophyll content. The best root growth and highest root activity of tomato seedlings were also found under the supplementary WR LEDs. Supplementary WR LEDs remarkably increased the stem firmness of the greenhouse-grown tomato seedlings, and increased the starch content in the leaves of greenhouse-grown tomato seedlings compared to the control. However, statistically significant differences did not occur in the sucrose, carotenoid contents, superoxide dismutase (SOD), and catalase (CAT) activities among the different supplemental lighting treatments. In conclusion, supplemental LED lighting could promote the growth and development of greenhouse-grown tomato seedlings grown under insufficient sunlight conditions. In addition, WR LEDs could obtain tomato seedlings with a higher net photosynthetic rate, higher root activity, and higher starch content compared with other treatments, which could be applied as supplementary lights in greenhouse-grown tomato seedlings grown in seasons with insufficient light.

The Effect of the Irradiation Dose and Time Factors on Producing Capacity of Lettuce and Leaf Vegetables in Photo-Culture Conditions

Optimisation of the irradiation dose and duration factors in conditions of lettuce-and-leaf vegetable photo-culture matches the goals of development of controllable plant cultivation systems for greenhouses and other protected-ground facilities. Based on the literature of the last years, it is specified that the DLI (Daily Light Integral) factor is paid great attention to in development of sustainable industrial phyto-technology with use of online meteorological and satellite-navigation data. The opportunities of control of the factors under consideration are demonstrated through the example of the author’s experiment in photo-culture conditions of two lettuce cultivars (Frisee and Adamant) made using an automated multi-layer City Farm installation in a room with controlled environment. During the experiment, the variable values of PPFD (photosynthetic photon flux density) in range (180–220) μmol/(m2s), daily photoperiod τф from 13 to 21 hours, vegetation duration t about 24 to 30 days were used with constant VLI, which is the new concept of vegetation light integral (VLI), was introduced similarly to DLI. It is found that the principle of reciprocity of irradiance parameters and time (the Bunsen-Roscoe law) is not met at constant dose. In terms of average producing capacity, it was possible to increase the level of biomass synthesis by 30 % for Frisee lettuce and by 36 % for Adamant lettuce. A series of partial dependences relating producing capacity of lettuce cultivars to DLI, photoperiod, and vegetation duration was obtained (the authors understand producing capacity as biomass over the vegetation period). The experiment results may be used as input data for the Virtual Agronomist software developed for controlled plant cultivation.

Effect of Radiation Quality and Relative Humidity on Intumescence Injury and Growth of Tomato Seedlings

Intumescence is a physiological disorder that affects some tomato (Solanum lycopersicum) cultivars grown in environments lacking ultraviolet radiation. Both far-red (FR) radiation and blue light have been shown to help mitigate this disorder. Thus, the objectives of this study were to characterize and compare intumescence injury and growth of various tomato cultivars propagated under different radiation qualities (Expt. 1) and to evaluate plant responses to the interactive effect of radiation quality and relative humidity (RH) (Expt. 2). Seedlings of six cultivars in Expt. 1 were grown under broad band white light (W), W and blue with (WBFR) or without (WB) FR radiation, and blue and red light with FR radiation (BRFR). Seedlings of four cultivars in Expt. 2 were grown under W or WBFR and a low (≈50%) or high (≈95%) RH. In both experiments, seedlings were grown under a daily light integral of ≈13 mol·m‒2·d‒1 (200 ± 4 μmol·m‒2·s‒1 for 18 h·d−1). FR radiation was provided using 20 ± 2 μmol·m−2·s−1 delivered throughout the entire photoperiod or at the end-of-day (EOD) in Expts. 1 or 2, respectively. Intumescence was generally suppressed when seedlings in Expt. 1 were grown under BRFR and WBFR, which also corresponded with the general response to stomatal conductance (gs). In contrast, seedlings grown under W had the highest incidence of intumescence, ranging from 23% to 69% across cultivars. The high blue photon flux (PF) ratio in WB was not effective at suppressing intumescence injury without FR radiation, although incidence and severity were lower compared with W. In Expt. 2, intumescence incidence was generally lower in seedlings grown under WBFR, and RH had small effects on intumescence. In both experiments, younger leaves were relatively less affected by intumescence, suggesting that a developmental factor is associated with the disorder. As expected, providing FR radiation resulted in a general increase in stem height across cultivars and in both experiments. The high RH provided in Expt. 2 also resulted in an increase in stem height. However, seedlings under low RH produced larger leaves, lower specific leaf area, and more shoot dry mass than those under high RH. Overall, our findings show that applying FR radiation helps suppress intumescence, but strategies are needed to minimize issues with excessive stem elongation.

Continuous lighting can improve yield and reduce energy costs while increasing or maintaining nutritional contents of microgreens.

Microgreens represent a fast growing segment of the edible greens industry. They are prized for their colour, texture, and flavour. Compared to their mature counterparts, microgreens have much higher antioxidant and nutrient content categorizing them as a functional food. However, current production practices in plant factories with artificial light are energy intensive. Specifically, the lack of sunlight within the indoor structure means all of the light must be provided via energy consuming light fixtures, which is energy intensive and costly. Plant growth is usually increased with the total amount of light provided to the plants - daily light integral (DLI). Long photoperiods of low intensity lighting (greater than 18h) providing the desired/target DLI can reduce the capital costs for light fixtures and electricity costs. This is achieved by moving the electricity use from peak daytime hours (high price) to off-peak hours (low price) during the night in regions with time-based pricing scheme and lowering the electricity use for air conditioning, if plant growth is not compromised. However, lighting with photoperiods longer than tolerance thresholds (species/cultivar specific) usually leads to plant stress/damage. Therefore, we investigated the effects of continuous 24h white light (CL) at two DLIs (~14 and 21 mol m-2 d-1) on plant growth, yield, and antioxidant content on 4 types of microgreens - amaranth, collard greens, green basil, and purple basil to see if it compromises microgreen production. It was found that amaranth and green basil had larger fresh biomass when grown under CL compared to 16h when the DLIs were the same. In addition, purple basil had higher biomass at higher DLI, but was unaffected by photoperiods. Plants grown under the CL treatments had higher energy-use-efficiencies for lighting (10-42%) than plants grown under the 16h photoperiods at the same DLI. Notably, the electricity cost per unit of fresh biomass ($ g-1) was reduced (8-38%) in all microgreens studied when plants were grown under CL lighting at the same DLIs. Amaranth and collard greens also had higher antioxidant content. Taken together, growing microgreens under CL can reduce electricity costs and increase yield while maintaining or improving nutritional content.