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Plant factories versus greenhouses: Comparison of resource use efficiency

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Abstract

Research on closed plant production systems, such as artificially illuminated and highly insulated plant factories, has offered perspectives for urban food production but more insight is needed into their resource use efficiency. This paper assesses the potential of this ‘novel’ system for production in harsh climates with either low or high temperatures and solar radiation levels. The performance of plant factories is compared with cultivation in traditional greenhouses by analysing the use of resources in the production of lettuce. We applied advanced climate models for greenhouses and buildings, coupled with a lettuce model that relates growth to microclimate. This analysis was performed for three different climate zones and latitudes (24–68°N). In terms of energy efficiency, plant factories (1411 MJ kg⁻¹ dry weight) outperform even the most efficient greenhouse (Sweden with artificial illumination; 1699 MJ kg⁻¹ dry weight). Additionally, plant factories achieve higher productivity for all other resources (water, CO2 and land area). With respect to purchased energy, however, greenhouses excel as they use freely available solar energy for photosynthesis. The production of 1 kg dry weight of lettuce requires an input of 247 kWhe in a plant factory, compared to 70, 111, 182 and 211 kWhe in greenhouses in respectively the Netherlands, United Arab Emirates and Sweden (with and without additional artificial illumination). The local scarcity of resources determines the suitability of production systems. Our quantitative analysis provides insight into the effect of external climate on resource productivity in plant factories and greenhouses. By elucidating the impact of the absence of solar energy, this provides a starting point for determining the economic viability of plant factories.

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... LED lighting can now be used as sole-source lighting for indoor cultivation in single or multi-layered growth rooms also called vertical farms or plant factories [48][49][50][51][52][53][54]. While one of the main drawbacks of using artificial lights for plant growth is the high electricity consumption [55], renewable energy technologies such as solar photovoltaics (PV) could provide an alternative to offset some of this energy demand and produce the electricity at the place where it is needed. ...
... Nevertheless, they also have the evident disadvantage of excluding sunlight which is a valuable and free resource. This results in the high energy consumption for lighting and climate control [55,112]. It has been estimated that between 70% and 80% of the electricity consumption in indoor growth rooms is due to lighting while the rest is mainly cooling and dehumidification [53,142]. ...
... Irrespectively of how advanced the lighting technologies are, there will always exist a certain investment and energy cost for artificial lighting compared to sunlight [51]. Under some circumstances and for certain species, the advantages of a fully controlled growth space and the possibility of year-round cultivation might outweigh some of those costs [52,53,55]. ...
Article
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High efficacy LED lamps combined with adaptive lighting control and greenhouse integrated photovoltaics (PV) could enable the concept of year-round cultivation. This concept can be especially useful for increasing the production in the Nordic countries of crops like herbaceous perennials, forest seedlings, and other potted plants not native of the region, which are grown more than one season in this harsh climate. Meteorological satellite data of this region was analyzed in a parametric study to evaluate the potential of these technologies. The generated maps showed monthly average temperatures fluctuating from −20 °C to 20 °C throughout the year. The natural photoperiod and light intensity also changed drastically, resulting in monthly average daily light integral (DLI) levels ranging from 45–50 mol·m−2·d−1 in summer and contrasting with 0–5 mol·m−2·d−1 during winter. To compensate, growth room cultivation that is independent of outdoor conditions could be used in winter. Depending on the efficacy of the lamps, the electricity required for sole-source lighting at an intensity of 300 µmol·m−2·s−1 for 16 h would be between 1.4 and 2.4 kWh·m−2·d−1. Greenhouses with supplementary lighting could help start the cultivation earlier in spring and extend it further into autumn. The energy required for lighting highly depends on several factors such as the natural light transmittance, the light threshold settings, and the lighting control protocol, resulting in electric demands between 0.6 and 2.4 kWh·m−2·d−1. Integrating PV on the roof or wall structures of the greenhouse could offset some of this electricity, with specific energy yields ranging from 400 to 1120 kWh·kW−1·yr−1 depending on the region and system design.
... The productivity of such systems is, however, effected by the light quality, intensity, and photoperiod [1][2][3]. As artificial lighting systems in CEAs account for a significant portion of the energy usage and costs [12,35], it is important to ensure that qualitative and quantitative aspects are optimized for the plants being cultivated. At present, artificial lighting used in indoor cultivation are designed to provide ...
... The productivity of such systems is, however, effected by the light quality, intensity, and photoperiod [1][2][3]. As artificial lighting systems in CEAs account for a significant portion of the energy usage and costs [12,35], it is important to ensure that qualitative and quantitative aspects are optimized for the plants being cultivated. At present, artificial lighting used in indoor cultivation are designed to provide photoperiodic extension, supplemental intensities or both. ...
... In CEAs, lighting energy costs often account for more than 50% of the total energy load, and as such, careful consideration should be made to ensure the most efficient approach is taken [12]. The LPD and PPE of the artificial light treatment is a representation of the equipment energy efficacy, and while it does not a reveal the effectiveness of the different photoperiods on biomass and metabolite accumulation, this is linked directly to the overall lighting energy requirements and costs. ...
Article
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Stevia rebaudiana cultivated in non-native tropical conditions tends to flower early, halting vegetative growth, resulting in lower biomass and yields of its valued steviol glycoside metabolites. While indoor cultivation allows manipulation of artificial lighting to mimic optimal conditions, it introduces an additional energy cost. The study objectives were to assess photoperiod manipulation as a lighting strategy to increase overall biomass and metabolite yields as well as to improve the efficacy of the electrical energy used for indoor cultivation of Stevia rebaudiana in non-native environmental conditions. Stevia was grown under artificial lighting with red, green, and blue wavelengths with photoperiods of 8 h, 12 h, 16 h, and intermittent light amounting to 16/24 h, each with a constant Daily Light Integral (DLI) of 7.2 mol m−2 day−1. Yield was measured as leaf dry weight biomass in combination with Liquid chromatography–mass spectrometry (LCMS) analysis of Stevioside and Rebaudioside A content. The photon flux density of the artificial and natural light as measured by a spectroradiometer, and the energy use data collected with a three-phase power quality logger, were compared for each treatment tested and to that from plants grown under natural light irradiation in a greenhouse. Yield and energy data were used to determine the efficacies of the lighting systems tested. Stevia plants under a continuous 16-h photoperiod (16H) had the highest productivity, resulting in the highest biomass accumulation and metabolite concentrations. The Stevioside and Rebaudioside A yields per plant were 975% higher than those obtained under natural daylight and day-neutral tropical photoperiod. Overall energy use and photon conversion efficacies were also highest under 16H at 65.10 g kWh−1 for biomass accumulation, 12.40 g kWh−1 for metabolite yields and 7.5 mg mol−1 for photon conversion. These findings support the application of photoperiod manipulation as a viable approach to increase productivity and improve energy use efficacies for indoor cultivation of Stevia rebaudiana plants under artificial lighting in non-native environments with the 16-h photoperiod under red and blue artificial light supplemented with green spectrum as the best option.
... Vertical farming potentially contributes to future food production, offering a technologically advanced production system. However, vertical farming is still a relatively new technology, and its cost-effectiveness, scalability, and environmental sustainability currently do not exceed conventional agricultural practices [28][29][30][31][32]. The opportunities and challenges involved can be grouped into four dimensions: (1) economic, (2) environmental, (3) social, and (4) political [29]. ...
... It allows layered growth, ensuring maximum yield per square meter of growing space, which is a feature that is especially advantageous in urban areas [11]. For example, a vertical farm can achieve lettuce yields per square meter of more than 80 times the yield of open-field agriculture and more than 12 times that of greenhouses [30][31][32][33][34]. In addition, indoor growth systems shield plants from outside weather and climate change [35]. ...
... In addition, the estimated total operating costs per square meter of growing space can be up to five times higher than that of a high-tech greenhouse [3]. Energy consumption is the primary source of these operational costs, with artificial lighting and HVAC as primary energy consumers [30]. According to Graamans et al. [30], the high use of artificial lighting in vertical farms makes greenhouses in Europe currently more efficient in terms of purchased energy. ...
Article
Full-text available
Vertical farming is on its way to becoming an addition to conventional agricultural practices, improving sustainable food production for the growing world population under increasing climate stress. While the early development of vertical farming systems mainly focused on technological advancement through design innovation, the automation of hydroponic cultivation, and advanced LED lighting systems, more recent studies focus on the resilience and circularity of vertical farming. These sustainability objectives are addressed by investigating water quality and microbial life in a hydroponic cultivation context. Plant growth-promoting rhizobacteria (PGPR) have been shown to improve plant performance and resilience to biotic and abiotic stresses. The application of PGPRs to plant-growing media increases microbial functional diversity, creating opportunities to improve the circularity and resilience of vertical farming systems by reducing our dependency on chemical fertilizers and crop protection products. Here, we give a brief historical overview of vertical farming, review its opportunities and challenges in an economic, environmental, social, and political context, and discuss advances in exploiting the rhizosphere microbiome in hydroponic cultivation systems.
... Decisions may be made based on various actuators used to regulate heating, lighting, cooling, dosing of CO 2 and fertilizers, dehumidification, irrigation, screening, fogging, as examples (Nelson, 1991;Uyeh et al., 2019Uyeh et al., , 2021Bhujel et al., 2020;Gadekallu et al., 2021). These actuators operate based on sensors providing feedback on measured data for the control loop set points configured in a computing device (Stanghellini, 2013;Graamans et al., 2018). ...
... In autonomous growing systems (Stanghellini, 2013;Graamans et al., 2018;Hemming et al., 2020), deployment of the more costly, high-precision sensors have added benefits such as durability and reduced capital costs in the long-term. Decisions based on imprecise measurements could result in poor plant growth (due to under-or over-heating) or irreversible damage and associated economic losses. ...
Article
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Irregular changes in the internal climates of protected cultivation systems can prevent attainment of optimal yield when the environmental conditions are not adequately monitored and controlled. Key to indoor environment monitoring and control and potentially reducing operational costs are the strategic placement of an optimal number of sensors using a robust method. A multi-objective approach based on supervised machine learning was used to determine the optimal number of sensors and installation positions in a protected cultivation system. Specifically, a gradient boosting algorithm, a form of a tree-based model, was fitted to measured (temperature and humidity) and derived conditions (dew point temperature, humidity ratio, enthalpy, and specific volume). Feature variables were forecasted in a time-series manner. Training and validation data were categorized without randomizing the observations to ensure the features remained time-dependent. Evaluations of the variations in the number and location of sensors by day, week, and month were done to observe the impact of environmental fluctuations on the optimal number and location of placement of sensors. Results showed that less than 32% of the 56 sensors considered in this study were needed to optimally monitor the protected cultivation system’s internal environment with the highest occurring in May. In May, an average change of −0.041% in consecutive RMSE values ranged from the 1st sensor location (0.027°C) to the 17th sensor location (0.013°C). The derived properties better described the ambient condition of the indoor air than the directly measured, leading to a better performing machine learning model. A machine learning model was developed and proposed to determine the optimal sensors number and positions in a protected cultivation system.
... Plants exhibit high plasticity to variations in light characteristics either when using radiation as a source of energy for photosynthetic processes, or when it represents a signal to regulate photo-morphogenetic responses via a complex system of wavelength-specific photoreceptors (Paik and Huq, 2019;Paradiso and Proietti, 2021). The optimal light setting, in terms of light quantity and quality is a key element of controlled environment agriculture (CEA) where all factors are controlled to optimize productivity and resource use efficiency (Graamans et al., 2018). ...
... Controlled environment agriculture technologies were introduced as early as the 1970s, in preparation for growing plants for food production during future NASA space missions (Gitelson et al., 1976). Today, CEA approaches are applied to plant production in contexts of climate changes scenarios, increasing population, extreme environmental conditions, unfavorable rural areas, and urban agriculture (Graamans et al., 2018). In advanced CEA plant growth facilities, light-emitting diodes (LEDs) have emerged as the most efficient and adaptable among artificial lighting systems. ...
Article
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Light-emitting diode lamps can allow for the optimization of lighting conditions in artificial growing environments, with respect to light quality, quantity, and photoperiod extension, to precisely manage resources and crop performance. Eruca vesicaria (L.) Cav. was hydroponically cultured under three light treatments to investigate the effect on yield and nutritional properties of rocket plants. A treatment of (W-12h) having a12/12 h light/dark at 600 μmol m−2 s−1 provided by LEDs W:FR:R:B = 12:2:71:15 was compared with two treatments of continuous lighting (CL), 24 h light at 300 μmol m−2 s−1 provided by cool white LEDs (W-CL), and by LED R:B = 73:27 (RB-CL). CL enhanced the growth of the rocket plants: total fresh biomass, leaf fresh weight, and shoot/root ratio increased in W-CL, and leaf dry weight, leaf dry matter %, root fresh and dry weight, and specific leaf dry weight (SLDW) increased in RB-CL. Total carbon content was higher in RB-CL, whereas total nitrogen and proteins content increased in W-12h. Both W-CL and RB-CL increased carbohydrate content in the rocket leaves, while W-CL alone increased the sugar content in the roots. Fibers, pigments, antioxidant compounds, and malic acid were increased by CL regardless of the light spectrum applied. Nitrate was significantly reduced in the rocket leaves grown both in W-CL and RB-CL. Thus, the application of CL with low light intensity can increase the yield and quality value of rocket, highlighting that careful scheduling of light spectrum, intensity, and photoperiod can improve the performance of the crop.
... When CO 2 is fertilized, it promotes crop growth and increases productivity (McGrath and Lobell, 2013). The amount of fertilized CO 2 and the productivity of crops do not have a linear relation, so finding the optimal amount of CO 2 is a matter of fact for precision agriculture (Linker et al., 1998;Kläring et al., 2007;Graamans et al., 2018). However, in greenhouse conditions, the CO 2 concentration is affected both by structural factors such as the ventilation rate and by environmental factors such as temperature, so it is not easy to saturate the optimal CO 2 concentration Roy et al., 2002). ...
... Therefore, the CO 2 consumption of the canopy can be measured easily, making efficient CO 2 fertilization possible. However, environmental fluctuations within a greenhouse are more complicated than a plant factory since greenhouses are not completely insulated (Graamans et al., 2018). In addition, plant growth factors should be considered along with various greenhouse environments because CO 2 concentrations are also affected by crop growth conditions. ...
Article
In greenhouses, photosynthesis efficiency is a crucial factor for increasing crop production. Since plants use CO2 for photosynthesis, predicting CO2 concentration is helpful for improving photosynthetic efficiency. The objective of this study was to predict greenhouse CO2 concentration using a long short-term memory (LSTM) algorithm. In a greenhouse where mango trees (Mangifera indica L. cv. Irwin) were grown, temperature, relative humidity, solar radiation, atmospheric pressure, soil temperature, soil humidity, and CO2 concentration were measured using complex sensor modules. Nine sensors were installed in the greenhouse. The averages of environmental factors from the nine sensors were used as inputs, and the average CO2 concentration was used as an output. In this experiment, LSTM, one of the recurrent neural networks, predicted changes in CO2 concentration from the present to 2 h later using historical data. The data were measured every 10 min from February. 1, 2017 to May 31, 2018, and missing data were interpolated with a linear method and multilayer perceptron. In this study, LSTM predicted the 2-h change in CO2 concentrations at an interval of 10 min with adequate test accuracy (R2 = 0.78). Therefore, the trained LSTM can be used to predict the future CO2 concentration and applied to efficient CO2 enrichment for photosynthesis enhancement in greenhouses.
... Investigations into the energy demand for the heating and lighting of greenhouses are often focusing on moderate latitudes around 50-55 • N [41,42] and not on 60-70 • N, which constitutes the north of Sweden. However, the calculations in [43] show that the energy demand of a GH in northern Sweden (Kiruna, at 67 • N), while roughly double compared to GHs in more southern locations (exemplified by Amsterdam and Abu Dhabi), is still lower than the energy demand of plant factories illuminated by LEDs. Moreover, as more than half of the energy demand comes from heating, using excess heat could potentially make GH farming in the north of Sweden competitive. ...
... Moreover, the required air flows between the GH and DC can also be calculated, thus providing a basis for dimensions and costs of ducting and fans. Since these calculations involve the peak requirements of the GH, this can be considered a new contribution to the field of DC-GH knowledge, in comparison to existing results that instead concern the total yearly energy consumption, see, e.g., [43] and the online calculation tool [59]. In the modeling, some reasonable assumptions have been made for simplicity (e.g., perfect air mixing and steady-state conditions). ...
Article
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As our world becomes increasingly digitalized, data centers as operational bases for these technologies lead to a consequent increased release of excess heat into the surrounding environment. This paper studies the challenges and opportunities of industrial symbiosis between data centers’ excess heat and greenhouse farming, specifically utilizing the north of Sweden as a case study region. The region was selected in a bid to tackle the urgent urban issue of self-sufficiency in local food production. A synergetic approach towards engaging stakeholders from different sectors is presented through a mix of qualitative and quantitative methods to facilitate resilient data-center-enabled food production. The paper delivers on possible future solutions on implementing resource efficiency in subarctic regions.
... While lettuce and leafy vegetables grow well at a DLI of 8-14 mol m -2 d -1 and temperatures of 18-21 °C (Dorais, 2003;Baumbauer et al., 2019;Pennisi et al., 2020), a DLI of at least 17-20 mol m -2 d -1 and 20-25 °C is required for the production of fruit vegetables such as tomatoes, pepper or strawberries (Schwarz et al., 2014). The high proportion of LED lighting on energy consumption as well as on the internal heat load of the cooling devices has been shown (Graamans et al., 2018). In order to still achieve a higher DLI, the photoperiod would have to be extended accordingly. ...
... The discrepancies on the last days are not fully understood yet, but can be assumed to be influenced by human activities inside the indoor farm as well as measurement errors and will be further investigated. Indoor farms require a large input of electrical energy for cooling due to a high internal heat load which is mainly influenced by the inefficiency of the LED fixtures (Graamans et al., 2018). Without considering plant reaction at this point, our results of the energy simulations suggest to favor light intensities of 240-290 µmol m -2 d -1 and longer photoperiods to produce fruit vegetables purely in terms of energy consumption for the given container indoor farm. ...
Conference Paper
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Indoor farming offers a high potential to supplement plant production. Nevertheless, the high electrical energy consumption remains a challenge to achieve profitability. For a container indoor farm at the University of Applied Science Weihenstephan-Triesdorf (HSWT) a simplified model to estimate the total energy consumption was developed. The model was validated by prediction of two measurement times in January (regarding an empty cultivation unit) and august (during pepper cultivation) (R² = 0.913 / RMSE = 1.6). The model was then used to analyze the impact of two set points for air temperature (20 °C and 25 °C), changes in the switch-on time of the LED over 24 h as well as varying photoperiods and light intensities with mean daily light integral (DLI) levels of 21 and 14 mol m-2 d-1 on the total electrical consumption. As expected a lower DLI needs up to 23-33 % less energy. Nevertheless, the results suggest a potential to reduce energy consumption by higher temperature of 2-8 %.
... Previous studies on plant factories have focused on the application of IT technologies and plant productivity based on light sources, such as lighting systems, or based on cooling and heating [5], renewable energy [6], and ventilation environments [7][8][9]. ...
Article
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In this study, a comparative economic analysis was conducted for typical greenhouses, plant factories with natural and artificial light, and those with only artificial light, based on the insulation, artificial light, and photovoltaic (PV) installation costs. In addition, the results of research on primary energy consumption and greenhouse gas (GHG) emissions from the use of fossil fuels were presented. By comparing the case-wise annual energy consumption, when all energy sources were converted into primary energy consumption based on the applied coefficients for collection, transport, and processing, to unify calculations for different fossil fuel energy sources, the case of the installed PV systems exhibited large reductions, of 424% and 340%, in terms of primary energy consumption and GHG emissions, respectively. Furthermore, electric heating resulted in higher primary energy consumption and GHG emissions than oil. When the economic analysis included the plant factory installation cost used to maintain the temperature required for plant growth in winter, the PV installation exhibited the highest cost; additionally, all plant factories showed an investment payback period of seven to nine years, which is comparable to typical greenhouses. Based on these results, we aim to reduce the use of fossil fuels for sustainable energy by combining architectural technology for improved energy performance in the agricultural environment.
... In a PFAL, over 50% of the electricity is consumed in lighting [5,6]. Therefore, a more efficient use of light is one approach to reduce electricity costs. ...
Article
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Dwarf tomatoes are advantageous when cultivated in a plant factory with artificial light because they can grow well in a small volume. However, few studies have been reported on cultivation in a controlled environment for improving productivity. We performed two experiments to investigate the effects of photosynthetic photon flux density (PPFD; 300, 500, and 700 μmol m−2 s−1) with white light and light quality (white, R3B1 (red:blue = 3:1), and R9B1) with a PPFD of 300 μmol m−2 s−1 on plant growth and radiation-use efficiency (RUE) of a dwarf tomato cultivar (‘Micro-Tom’) at the vegetative growth stage. The results clearly demonstrated that higher PPFD leads to higher dry mass and lower specific leaf area, but it does not affect the stem length. Furthermore, high PPFD increased the photosynthetic rate (Pn) of individual leaves but decreased RUE. A higher blue light proportion inhibited dry mass production with the same intercepted light because the leaves under high blue light proportion had low Pn and photosynthetic light-use efficiency. In conclusion, 300 μmol m−2 s−1 PPFD and R9B1 are the recommended proper PPFD and light quality, respectively, for ‘Micro-Tom’ cultivation at the vegetative growth stage to increase the RUE.
... Working costs were negligible and similar for natural soil and Sustain soil while, it was steep for hydroponics and aeroponics (17 and 23 times than soil). Natural soil is lost to degradation due to various causes that leads to soil erosion (Guerra et al., 2020) and soil-independent alternatives like hydroponics and aeroponics require technical expertise, and have high infrastructure and working costs (Graamans et al., 2018) which are taken care of by Sustain soil. ...
Article
Limitation to cultivable area and increasing food demand has steered development of urban farming. Practice of container gardening, patio gardening and rooftop gardening cause soil erosion while soil-less systems like hydroponics and aeroponics are expensive. Balancing traditional and contemporary methods need to be identified. We assessed the growth and nutrient values of functional food wheatgrass (Triticum aestivum L.) cultivated in different growth media – soil, hydroponics, aeroponics and paper-pulp based potting mix soil. Height, fresh weight, protein, minerals, and vitamins composition of wheatgrass plantlets were estimated. Construction and running costs for six-month period were compared. Plantlets harvested from potting mix soil had highest height & weight gain (at 88.67 cm and 15.13 gm) and all-around nutrient contents over others. Cost analysis shows that working costs for potting mix soil-based systems are most productive for a long duration (17x and 23x cheaper than hydroponics and aeroponics). The current study shows suitability of potting mix soil over other cultivation methods for wheatgrass for urban farming needs. Potting mix does not contribute to soil erosion as in case of natural soil based urban farming. Our results support the idea of utilization of potting mix for urban agricultural needs without indulging in cost- and technology- invested methods.
... To produce a single head of lettuce, this translates to an electrical energy consumption of approximately 1.0-1.6 kW h that can be referred to lighting. Nonetheless, in terms of overall energy consumption per produced kilogram dry weight, vertical indoor farms have been shown to outperform even the most efficient greenhouses [13]. However, the general demand of such plant factories for purchased energy is much higher than in the latter case and reduces corresponding profit margins. ...
Article
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Vertical farming is considered to play a crucial role in future food supply. Until today, the high amount of electrical energy required for artificial lighting has been problematic in this context. Various possibilities for increasing efficiency through adapted lighting conditions have been and are being investigated. However, comparably little attention is paid to increasing utilance, i.e., the amount of photons that can effectively be used by the plant. In this work, a novel targeted lighting strategy is therefore proposed that allows for a dynamic adaptation of the luminaires’ light distribution to match the effective crop size at each stage of plant growth in a fully-automated manner. It is shown that the resulting utilance can significantly be increased compared to standard full-coverage lighting. Moreover, it is found that the proposed strategy is likely to consume less than half of the electrical energy usually required for the latter. An additional increase in system efficiency can be prognosticated and the potential energy savings are estimated based on assumptions of future LED generations derived from literature.
... Furthermore, PFAL enable to explore the vertical dimension by using multilayers cultivation systems which result in greater yield per unit of cultivation area as compared to more traditional cultivation systems (e.g., on-soil and greenhouse) (Kalantari et al., 2017). In these systems, elevate water saving may be achieved, thanks to the use of a closed loop water cycle provided by both hydroponics and dehumidification of evapotranspired water from the atmospheric air (Graamans et al., 2018). The radiation use efficiency (RUE) is generally higher than in open field and greenhouse systems, although it shall be considered that, when plants are grown in absence of solar radiations, light comes at relevant cost (Pennisi et al., 2019b). ...
... According to Asian plant factories the artificial lighting can represent up to 85% of the total electrical consumption (Kozai, 2013). Since the LEDs still have a high inefficiency, the contribution of the lighting to the internal heat load of an indoor farm remains high (Graamans et al., 2018). ...
... The building energy simulations were performed using EnergyPlus, which is an open-source whole building energy simulation program. It is commonly used for modeling greenhouse energy consumption (Graamans et al., 2018;Nadal et al., 2017;Pakari and Ghani, 2019a). Enr-gyPlus consists of three main modules. ...
Article
Cooling is essential for greenhouse crop cultivation in hot areas. The selection of a suitable cooling system size for greenhouses is challenging since various environmental and structural factors are involved. In this study, a regression model was developed that relate input factors, including ambient air temperature (30-44 • C), ambient relative humidity (0.15-0.5), greenhouse air temperature (20-35 • C), cover transmission (0.3-0.9), cover U value (1-6 W/m 2 K), and ground soil thermal conductivity (0.1-1.5 W/m K), to a response, the maximum cooling load of a greenhouse (W/m 2). The model was developed using a central composite design and the maximum cooling load was calculated using EnergyPlus. The EnergyPlus results were validated against measured cooling loads of eight experimental greenhouses. The cooling loads predicted by EnergyPlus matched the calculated cooling loads from the experimental measurements within 12.4%. While the regression equation's predictions matched the experimental measurements within 13.1%. The results showed that the effect of the factors on the cooling load in order of significance from high to low were as follows, soil thermal conductivity, cover transmission , greenhouse air temperature, ambient air temperature, cover U value, and ambient air relative humidity. The developed regression equation provides a straightforward means to predict the cooling system size for greenhouses.
... Consequently, their products need to have some additional value compared to conventionally grown crops. Examples of added value are: 1. Distribution channels can be less complicated because the location of the farm is very close to its final destination; 2. crops-for example, ornamentals and cannabis-can have a higher quality from being grown in a controlled environment; 3. crops can be marketed as being more resource efficient, and hence environmentally friendly, adding to their value [11]; and 4. certain crops with high demand during their conventional off-season might be able to command a premium price. Essentially, vertical farm operators must have some sort of marketing advantage to counteract the higher operational costs of running a vertical farm. ...
Article
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Vertical farming (VF) is a newer crop production practice that is attracting attention from all around the world. VF is defined as growing indoor crops on multiple layers, either on the same floor or on multiple stories. Most VF operations are located in urban environments, substantially reducing the distance between producer and consumer. Some people claim that VF is the beginning of a new era in controlled environment agriculture, with the potential to substantially increase resource-use efficiencies. However, since most vertical farms exclusively use electric lighting to grow crops, the energy input for VF is typically very high. Additional challenges include finding and converting growing space, constructing growing systems, maintaining equipment, selecting suitable plant species, maintaining a disease- and pest-free environment, attracting and training workers, optimizing the control of environmental parameters, managing data-driven decision making, and marketing. The objective of the paper is to highlight several of the challenges and issues associated with planning and operating a successful vertical farm. Industry-specific information and knowledge will help investors and growers make informed decisions about financing and operating a vertical farm.
... The fastest growing sector in industrialized countries addressing this development is controlled-environment agriculture (CEA), in particular greenhouses with supplemental lighting and vertical indoor farming for vegetable production 8,9 . Such high-tech growing methods promise improvements on a host of sustainability metrics 10 but perform poorly on energy intensity [11][12][13] . The prospect is that renewable energy will mitigate potentially high carbon emissions associated with energy supply 10,13,14 . ...
Article
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Modern greenhouses and vertical farming projects promise increased food output per unit area relative to open-field farming. However, their high energy consumption calls for a low-carbon power supply such as solar photovoltaic and wind, which adds to cost and overall land footprint. Here we use geospatial and mathematical modelling to compare open-field and two indoor farming methods for vegetable production in nine city-regions chosen globally with varying land availability, climatic conditions and population density. We find that renewable electricity supply is more costly for greenhouses per unit energy demand satisfied, which is due to the greater fluctuation in their energy demand profile. However, greenhouses have a lower energy demand per unit food output, which makes them the least land-intensive option in most of the analysed regions. Our results challenge the land-savings claims of vertical farming compared with open-field production. We also show that regionalizing vegetable supply is feasible in most regions and give recommendations based on the regional context.
... The results from the synergies reviewed suggest INTRODUCTION Urban farming has been identified by a number of authors to provide promising solutions to secure food supplies, produce more sustainable food, and reduce pressure on agricultural land by shifting food production to urban environments and buildings (Cockrall-King, 2012;Thomaier et al., 2014;Eigenbrod and Gruda, 2015;Goldstein et al., 2016;Bustamante, 2018). Urbanvertical farming is primarily promoted for its potential to extend the seasonal availability of regional foods, especially in Northern Europe (Graamans et al., 2018;Orsini et al., 2020). Examples of urban-vertical farming have seen a dramatic increase in recent years, attracting considerable interest and funding (Weidner et al., 2019;Orsini et al., 2020;S2G, 2020;Agritecture, 2021). ...
Article
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Vertical farms have expanded rapidly in urban areas to support food system resilience. However, many of these systems source a substantial share of their material and energy requirements outside their urban environments. As urban areas produce significant shares of residual material and energy streams, there is considerable potential to explore the utilization of these streams for urban agriculture in addition to the possibility of employing underutilized urban spaces in residential and commercial buildings. This study aims to explore and assess the potential for developing more circular vertical farming systems which integrate with buildings and utilize residual material and energy streams. We focus on the symbiotic development of a hypothetical urban farm located in the basement of a residential building in Stockholm. Life cycle assessment is used to quantify the environmental performance of synergies related to energy integration and circular material use. Energy-related scenarios include the integration of the farm's waste heat with the host building's heating system and the utilization of solar PV. Circular material synergies include growing media and fertilizers based on residual materials from a local brewery and biogas plant. Finally, a local pickup system is studied to reduce transportation. The results point to large benefits from integrating the urban farm with the building energy system, reducing the vertical farm's GHG emissions up to 40%. Synergies with the brewery also result in GHG emissions reductions of roughly 20%. No significant change in the environmental impacts was found from the use of solar energy, while the local pickup system reduces environmental impacts from logistics, although this does not substantially lower the overall environmental impacts. However, there are some trade-offs where scenarios with added infrastructure can also increase material and water resource depletion. The results from the synergies reviewed suggest Martin et al. Urban Symbiotic Vertical Farming that proximity and host-building synergies can improve the material and energy efficiency of urban vertical farms. The results provide insights to residential building owners on the benefits of employing residual space for urban food provisioning and knowledge to expand the use of vertical farming and circular economy principles in an urban context.
... Eventually, water may leave VFS only as part of the harvested product, which would reduce water use by ~90% compared with greenhouses 69 and by ~99% compared with the open field. However, VFS are not unique in their potential for water recycling, as closed greenhouses with active cooling can achieve similar efficiencies 69 . High-level water treatment should theoretically allow for near-indefinite reuse of nutrient solutions. ...
Article
Vertical farming can produce food in a climate-resilient manner, potentially emitting zero pesticides and fertilizers, and with lower land and water use than conventional agriculture. Vertical farming systems (VFS) can meet daily consumer demands for nutritious fresh products, forming a part of resilient food systems—particularly in and around densely populated areas. VFS currently produce a limited range of crops including fruits, vegetables and herbs, but successful implementation of vertical farming as part of mainstream agriculture will require improvements in profitability, energy efficiency, public policy and consumer acceptance. Here we discuss VFS as multi-layer indoor crop cultivation systems, exploring state-of-the-art vertical farming and future challenges in the fields of plant growth, product quality, automation, robotics, system control and environmental sustainability and how research and development, socio-economic and policy-related institutions must work together to ensure successful upscaling of VFS to future food systems.
... Eventually, water may leave VFS only as part of the harvested product, which would reduce water use by ~90% compared with greenhouses 69 and by ~99% compared with the open field. However, VFS are not unique in their potential for water recycling, as closed greenhouses with active cooling can achieve similar efficiencies 69 . High-level water treatment should theoretically allow for near-indefinite reuse of nutrient solutions. ...
Article
Vertical farming can produce food in a climate-resilient manner, potentially emitting zero pesticides and fertilizers, and with lower land and water use than conventional agriculture. Vertical farming systems (VFS) can meet daily consumer demands for nutritious fresh products, forming a part of resilient food systems—particularly in and around densely populated areas. VFS currently produce a limited range of crops including fruits, vegetables and herbs, but successful implementation of vertical farming as part of mainstream agriculture will require improvements in profitability, energy efficiency, public policy and consumer acceptance. Here we discuss VFS as multi-layer indoor crop cultivation systems, exploring state-of-the-art vertical farming and future challenges in the fields of plant growth, product quality, automation, robotics, system control and environmental sustainability and how research and development, socio-economic and policy-related institutions must work together to ensure successful upscaling of VFS to future food systems.
... The United Nations Food and Agriculture Organisation (FAO) foresees that only one-third of the arable land per person in 1970 will be available in 2050 [4]. Vertical farms, which are multi-storey plant factories [5], are designed to provide rapid and uniform product growth of a high quality [6]. Recent work shows that various types of crops, e.g., leafy greens, lettuce, vine crops, and tomatoes [7], can be grown in closed farming systems. ...
Article
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The increase in global population, which negatively affects energy consumption, CO2 emissions, and arable land, necessitates designing sustainable habitation alternatives. Self-sufficient high-rise buildings, which integrate (electricity) generation and efficient usage of resources with dense habitation, can be a sustainable solution for future urbanisation. This paper focuses on transforming Europoint Towers in Rotterdam into self-sufficient buildings considering energy consumption and food production (lettuce crops) using artificial intelligence. Design parameters consist of the number of farming floors, shape, and the properties of the proposed façade skin that includes shading devices. Nine thousand samples are collected from various floor levels to predict self-sufficiency criteria using artificial neural networks (ANN). Optimisation problems with 117 decision variables are formulated using 45 ANN models that have very high prediction accuracies. 13 optimisation algorithms are used for an in-detail investigation of self-sufficiency at the building scale, and potential sufficiency at the neighbourhood scale. Results indicate that 100% and 43.7% self-sufficiencies could be reached for lettuce crops and electricity, respectively, for three buildings with 1800 residents. At the neighbourhood scale, lettuce production could be sufficient for 27,000 people with a decrease of self-sufficiency in terms of energy use of up to 11.6%. Consequently, this paper discusses the potentials and the improvements for self-sufficient high-rise buildings.
... In fact, over the past few years, the greenhouse industry has been transformed to include modern technologies allowing farmers to grow a consistent product all year round using far fewer resources than conventional production (Tuomisto 2019). The main part of this transformation is the introduction of vertical systems that have been proposed as a concept to address the issue of sustainability (Graamans et al. 2018) and as a solution to improving food production involving land and water use optimization (Kalantari et al. 2020;Benke and Tomkins 2017;Bao et al. 2018;Yeşil and Tatar 2020). Vertical systems consist of growing crops in vertically stacked layers under a protected environment to limit the use of the agricultural land and therefore the ecological footprint of agriculture (Anda and Shear 2017). ...
Article
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Greenhouse farming is essential in increasing domestic crop production in countries with limited resources and a harsh climate like Qatar. Smart greenhouse development is even more important to overcome these limitations and achieve high levels of food security. While the main aim of greenhouses is to offer an appropriate environment for high-yield production while protecting crops from adverse climate conditions, smart greenhouses provide precise regulation and control of the microclimate variables by utilizing the latest control techniques, advanced metering and communication infrastructures, and smart management systems thus providing the optimal environment for crop development. However, due to the development of information technology, greenhouses are undergoing a big transformation. In fact, the new generation of greenhouses has gone from simple constructions to sophisticated factories that drive agricultural production at the minimum possible cost. The main objective of this paper is to present a comprehensive understanding framework of the actual greenhouse development in Qatar, so as to be able to support the transition to sustainable precision agriculture. Qatar’s greenhouse market is a dynamic sector, and it is expected to mark double-digit growth by 2025. Thus, this study may offer effective supporting information to decision and policy makers, professionals, and end-users in introducing new technologies and taking advantage of monitoring techniques, artificial intelligence, and communication infrastructure in the agriculture sector by adopting smart greenhouses, consequently enhancing the Food-Energy-Water Nexus resilience and sustainable development. Furthermore, an analysis of the actual agriculture situation in Qatar is provided by examining its potential development regarding the existing drivers and barriers. Finally, the study presents the policy measures already implemented in Qatar and analyses the future development of the local greenhouse sector in terms of sustainability and resource-saving perspective and its penetration into Qatar’s economy.
... Plant factories, also known as vertical farms, are fast evolving agricultural systems that integrate a variety of modern technologies; they can cultivate crops on multiple layers and achieve high-efficiency and -quality production (Graamans et al., 2018;Kozai, 2013;Kozai et al., 2019). Besides, plant factories are almost completely insulated from the external climate and allow internal environmental factors such as light, temperature, humidity, CO 2 concentration, and nutrient solution to be controlled precisely and automatically; thus, they are rarely constrained by climatic conditions and geographical location. ...
... The climate controller simulates commercially available greenhouse control equipment to enable climate management by means of heating, (mechanical) ventilation, (de)humidification, shading, artificial lighting and carbon dioxide enrichment, amongst others. KASPRO is continuously updated and validated in research projects to include innovations in greenhouse technology and crop management strategies (Luo, De Zwart et al. 2005, Kempkes, De Zwart et al. 2017, Graamans, Baeza et al. 2018). ...
Conference Paper
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The ongoing global push for sustainability has motivated both the greenhouse horticulture and aquaculture sectors to explore the potential of geothermal energy for heating as an alternative to fossil fuels. To improve heat use efficiency of geothermal wells these food production systems can be integrated into an aquaponic-based thermal treatment network. Within this network the fish farm utilizes residual geothermal heat supplied by the greenhouse and heat from the geothermal well directly at moments that greenhouse heat demand is low. The EU funded GEOFOOD project aims to analyze in detail how to optimize the design and operation of such aquaponic facilities that use geothermal energy. To that end a predictive model was developed which simulates the heat balances present throughout the thermal treatment network. The model enables the user to compose a sequence of geothermal wells, greenhouses and aquaculture facilities for which different scenarios can be explored by selecting several types of greenhouse, different crops and fish species as well as climates. Three different climate regions with potential for geothermal energy use for aquaponic production have been selected to perform a scenario study; The Netherlands, Iceland and Slovenia. The simulated aquaponic system consisted of a 5 ha Venlo type greenhouse for tomato production and an indoor pike-perch fish farm. It is found that for a greenhouse located in the Netherlands geothermal heat extraction can be increased with 31% by combining it with an indoor pike-perch fish farm of 6544 m 2 , without the need of alternative energy sources during peak demands.
... Indeed, cultivation technologies using the multi-layer stacking enabled by VFS (e.g., the nutrient film technique) during lettuce growth can reduce water use by 96% compared with the traditional, non-recirculating methods often deployed in a glasshouse environment. While recirculating methods can be used in glasshouses, the absence of vertical stacking still results in an unfavourable ratio between water use and production per unit of area in VFS compared with glasshouse growth [10]. VFS also offers reduced utilisation of outdoor spaces for farmland and limits post-farm-gate emissions when situated close to urban areas [9,11]. ...
Article
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Intensive agriculture is essential to feed increasing populations, yet requires large amounts of pesticide, fertiliser, and water to maintain productivity. One solution to mitigate these issues is the adoption of Vertical Farming Systems (VFS). The self-contained operation of these facilities offers the potential to recycle agricultural inputs, as well as sheltering crops from the effects of climate change. Recent technological advancements in light-emitting diode (LED) lighting technology have enabled VFS to become a commercial reality, although high electrical consumption continues to tarnish the environmental credentials of the industry. In this review, we examine how the inherent use of electricity by VFS can be leveraged to deliver commercial and environmental benefits. We propose that an understanding of plant photobiology can be used to vary VFS energy consumption in coordination with electrical availability from the grid, facilitating demand-side management of energy supplies and promoting crop yield.
... Nowadays, artificial lighting is widely accepted for horticultural crops produced under controlled environments such as plant factories and space agriculture (Graamans et al. 2018). The recent development of LEDs (lightemitting diodes), which allows targeted manipulation of the spectrum composition and intensity for artificial lighting, has provided an opportunity to maximize crop productivity and accumulation of health beneficial compounds for both commercial and research perspectives in greenhouse crop cultivation (Kozai 2016, Pattison et al. 2018, Kusuma et al. 2020, Paradiso and Proietti 2021. ...
Article
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Mesembryanthemum crystallinum is an annual succulent plant that is being used as an emerging healthy leafy vegetable. To investigate the growth and physiological response of M. crystallinum to artificial lighting, five different light treatments were applied at 150 µmol(photon) m-2 s-1, which were white (W), different rations of red/blue (B) (15, 40, and 70%B), and blue (100%B), respectively. Our results showed that plants could gain as much as edible leaf area and dry mass with a certain ratio of blue (40%) in comparison with W. Plants grown under 100%B resulted in reduced photosynthetic rate, leaf area, and fresh mass compared with W. Adding blue fraction in the light regime enhanced the photosynthetic performance by influencing the amount of chlorophyll (Chl), Chl a/b, and specific leaf area. Under red/blue treatments, the electron transport rate and effective quantum yield of both PSII and PSI increased, while the nitrate content was reduced and flavonoids and total antioxidant capacity were unaffected.
... The lighting consumes energy while generating heat at the same time. The cooling demands and lighting requirement contributes significantly to the overall energy consumption [1] [2]. Plant growth requires the right balance of light and a controlled environment at the right temperature. ...
Conference Paper
Energy is one of the largest operating cost for indoor farms in tropics. Two most significant elements of energy consumption comes from indoor air cooling and LED lighting. The heat emitted by the LED lights further increases the cooling load. There is a need to develop a new way to cool both the indoor air and LED lights with much lower energy consumption. In this paper, an integrated LED and microclimate cooling system is presented. The system combines the LED with the plant growth tray in a modular design which can be replicated for a larger scale indoor farm. The modular plant growth chamber has built in features which allows the nutrient water to flow through the growth tray and return to the nutrient water tank where it is chilled before being recirculated. The effect of the flowing chilled nutrient water on the air temperature and humidity in the growth environment is evaluated through a microclimate model. The result of this analysis shows that there is up to 10°C reduction in the air temperature near the root zone of the plant. There is also a reduction in moisture content in the air when the nutrient water is circulated at temperature of less than 15°C. This microclimate model is also able to simulate the cooling load required to maintain an ideal environment for plant growth. The simulation result shows that modular plant growth chamber is able to control both the temperature and humidity while maintaining a balance of the energy consumption.
... In plant factories with high energy use, lighting factors should be optimised based on resource use efficiency including lighting electricity (Graamans, Baeza, van den Dobbelsteen, Tsafaras, & Stanghellini, 2018). Simulationbased analysis made it possible to find out the optimal lighting arrangement and distance for maximal light use efficiency for photosynthesis in lettuce canopies (Kim, Kang, & Son, 2020). ...
Article
Although ultraviolet-B (UV-B, 280–315 nm) radiation has been known as an effective elicitor for improving bioactive compound contents in plants, its practical application to plant factories is still in its infancy. This study aimed to develop an evaluation method for optimising the lighting design of UV-B radiation in plant factories. To this end, a prediction model of phenolic content was adapted for kale (Brassica oleracea L. var. acephala) plants grown in a plant factory using an optical simulation in a three-dimensional plant model. The prediction model was calibrated using experimental data with different 310 nm UV-B light-emitting diode (LED) arrangements. UV-B radiation significantly enhanced the total phenolic content, total flavonoid content, UV-B absorbing pigment content, and antioxidant capacity in kale plants. In scenario analysis with variables of lighting system, such as vertical or horizontal lighting distance and lighting angle of UV-B LED, the spatial distribution of phenolic accumulation was estimated using the calibrated model and simulated UV-B radiation interception. Although the uniformity and efficiency were opposite in most scenarios, both values for phenolic production increased with changes in horizontal position. The annual yields per electrical energy consumed for producing total phenolics and flavonoids were expected to improve by 14.2 and 34.0%, respectively, assuming the addition of UV-B LED as the optimal lighting design among the scenarios. These evaluation and optimisation methods using model-based simulations will help to design custom UV-B lighting systems for the production of bioactive compounds in commercial plant factories.
... Vertical farms with artificial lighting tend to use substantially larger amounts of energy as electricity is required for lighting, maintaining growing temperatures, ventilation, and other environmental controls (Beacham et al., 2019). Graamans et al. (2018) simulated the potential productivity of indoor and greenhouse farming in three cities, finding that compared to indoor farming facilities, the productivity of greenhouses would be more dependent on the external climate, but greenhouses would always use less energy. In Arizona, USA, Barbosa et al. (2015) estimated that a hydroponics system in a heated greenhouse could potentially produce 11 times more lettuce than conventional soil-based farming, but would require 82 times more energy as a result of the electricity usage. ...
Article
Urban farming can improve cities’ food security and resilience, but the performance of different farming systems with respect to land and investment constraints has not been systematically investigated. Here, we compared conventional soil-based farming, vertical farming with natural lighting (Vnat), and indoor vertical farming. This study aimed to compare (1) the dynamic production of leafy vegetables over time given the same amount of investment and land constraints, (2) the associated water and energy use, and (3) the global warming potential (GWP) of the urban farming sector if each of the three farming systems was solely used in the tropical city-state of Singapore. A system dynamics (SD) model was constructed to map the potential quantity of leafy vegetables produced, together with the water and energy use of each farming system. The land and monetary investment constraints were set at an additional 0.3% of the total land area of Singapore and an annual investment of SGD 10–20 million (0.001–0.005% of Singapore's annual GDP). Vnat farming was predicted to have the highest production level (110,000 t) and self-sufficiency (76.9% of total demand) by 2050 based on the SD model. This would be >3 times the self-sufficiency level achieved by indoor and soil-based farming systems given the same investment and land constraints. Indoor farming was simulated to use <14% the land area of Vnat while soil-based farming exhausted the additional 0.3% of the land allocated. Indoor farming was also the most energy intensive system, requiring 100 times more than Vnat farming. Comparison of the GHG emission rates showed that indoor farming had the greatest GWP—at 2.51 kg CO2-eq per kg of lettuce produced. Our results suggest that Vnat farming may be the best form of urban farming system to provide large amounts of food in Singapore, considering the production level, the amount of resources used, and the environmental impacts.
... Aspects of systems understanding outlined in the scope-setting editorial is reflected in the publications of Fernandes and Nair (1986), Thornton et al. (2009), Rigby and Cáceres (2001), De Ponti et al. (2012, and Giller et al. (2011). Spedding (1976) also highlighted the need for understanding the effects and impacts of agricultural inputs and the weather/climate drivers and diseases (and here we include pests and weeds) on system (1985), Conway (1987), Pretty et al. (2000), Schipanski et al. (2014), Wolfert et al. (2017), Graamans et al. (2018) and Fritz et al. (2019). Another theme in the opening editorial was the need for multiple methodologies. ...
Article
This editorial observes 200 volumes of Agricultural Systems. Volume 1, dated January 1976, began with an article by the inaugural editor, C.R.W. Spedding (1976), that laid the foundations for this journal. We echo that first editorial with this contribution to begin Volume 201 and review some aspects of the history of the journal. To celebrate those 200 volumes, we have prepared a Collection of the highly-cited papers published over the last 46 years in those volumes. Here we present brief summary information about the journal, compare themes common to the opening editorial and the highly-cited papers, and conclude with an intent to review the aims and scope of the journal over the next year or so.
... This technology is particularly suitable for the cultivation of small-sized plants with a short production cycle, such as leafy vegetables and herbs, and valuable medicinal plants [1,3,4]. The consumption of energy, water, carbon dioxide, and land area for producing a unit mass of lettuce in a plant factory is much lower than in greenhouse cultivation, because of the possibility of cultivating plants on many levels, using closed fertigation systems, and recovery of water lost due to transpiration [5]. The most important factors limiting the development of technologies of plant production in plant factories are the high costs of investment and energy for artificial lighting. ...
Article
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The study examined the influence of light quality on the growth and nutritional status of romaine lettuce grown in deep water culture with a floating raft system using two different nutrient solutions. Four spectra of LED light were used with different ratios of R, G, and B lights (80:10:10, 70:10:20, 60:10:30, and 70:18:12). Two nutrient solutions with a low (A) and moderately high (B) nutrient content were used. Regardless of the nutrient solution, the RGB 70:18:12 light promoted the production of leaf biomass as well as inhibited the accumulation of K and Mg in the leaves. Moreover, those plants were characterized by a low Nitrogen Balance Index (NBI) and a high flavonol index. In the last week of cultivation, there was a strong decrease in K, P, and nitrates in the nutrient solution, and an increase in Ca. In the final stage of growth, symptoms of withering of the tips of young leaves (tipburn) were observed on the plants. The most damage was observed on the plants growing under 70:10:20, 70:18:12, and with the higher concentration of minerals in the solution (B).
Article
The rapidly growing population and increasing urbanization have created the need to produce more food and transport it safely to urban areas where the majority of global consumers live. Open-field agriculture and food distribution systems have a lot of food waste, and, in parallel, the largest percentage of available arable land is already occupied. In most cases, food produced by compatible agricultural methods needs to be frozen and travel several miles until it reaches the consumer, with high amounts of greenhouse gas (GHG) emissions produced by this process, making it an unsustainable method with huge amounts of CO2 emissions related with fresh food products. This research contains an extensive literature review based on 165 international publications (from 2006–2022) describing and analyzing the efficiency and impact of controlled-environment agriculture (CEA) methods, and more precisely, greenhouses (GHs) and vertical farms (VFs), in the environmental footprint of food production and consumption. Based on various publications, we could draw the conclusion that VFs could highly influence a greener transition to the sustainability of urban consumption with reduced CO2 emissions sourcing from food transportation and limited post-harvest processes. However, there is a significant demand for further energy efficiency, specifically when it comes to artificial lighting operations inside VFs. A large-scale implementation of VFs that operate with renewable energy sources (RES) could lead to significant urban decarbonization by providing the opportunity for integrated energy–food nexus systems. Under this direction, VFs could optimize the way that cities interact with meeting the food and energy demand in densely urbanized areas.
Article
Tomato greenhouses at high latitudes (≥58°North) require supplemental light to enable high yields and year-round production. Supplemental light systems can differ in lamp type, high-pressure sodium (HPS) or light emitting diode (LED), and also vary in lamp capacity. Based on a combined greenhouse climate, tomato yield, and greenhouse economics model, a methodology was developed, for determining the optimal supplemental light system, dependent on local climate and economic conditions. Two optimisation objectives were considered separately, maximal energy use efficiency (EUE) and maximal net financial result (NFR). The developed methodology was applied to four different greenhouse locations in Norway. At each location, both optimisation objectives were reached with LEDs. The optimal lamp capacities range from 256 to 341 μmol m⁻² s⁻¹ (maximal EUE) and 302–323 μmol m⁻² s⁻¹ (maximal NFR). The economically optimal lamp capacity is little sensitive to climate conditions. At the lamp type respective NFR maxima, LEDs resulted, on average, in 10% higher tomato yield, 102.2 NOK m⁻² year⁻¹ higher NFR, and 35% higher EUE. Consequently, switching from HPS lamps to LEDs enables increasing productivity, energy efficiency and profitability of greenhouse tomato production. Furthermore, the difference between EUE and NFR optima was, on average, 24% lower in terms of EUE and 56% lower in terms of NFR, when using LEDs instead of HPS lamps. On farm-scale, the proposed methodology can be used as decision-support-tool for selecting an efficient and profitable supplemental light system for greenhouse tomato production, dependent on local climate and economic conditions.
Article
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Plant factory artificial light (PEAL) is an attractive technology for producing high-value plants and medical-grade herbs. The PFAL research and development in Thailand are in their early stages. This article aims to design and construct the lab-scale PFAL, which includes several key features such as the lighting quality, the controls of the environment, and the embedded technology monitoring system. The lab-scale PEAL must evaluate the preliminary results of the artificial light parameters, resources consumption, the plant production yield, and the correlation between LED artificial light and the plant yields. The results demonstrated that our lab-scale PFAL consists of 27 m3 cultivation volumes. White-LED T8 (4091K) artificial light emitted, on average, the PPFD of 187±23 µmol m-2 s-1 with an R:B ratio of 1.8. The lettuce production yields show a strong positive correlation with the PPFD. The lettuce production yield is 76.23 g plant-1 under the temperature of 24.05℃, RH of 79.3%, and 923 ppm of CO2 concentration with a light period of 16/8 h. The PC-based monitoring and data acquisition control worked well during the crop experiments. The environmental parameters indicated that the results did not differ from the other PFALs. Electrical energy consumption data were also reasonable at 45%, 37%, and 17% of LED artificial light, air condition units, and other types of equipment, respectively. The artificial light sources have to improve the light uniformity and increase intensity. The lab-scale PFAL is very helpful in developing students’ skills in education and disseminating the knowledge and technical design of our PFAL to academic services. For future studies, efforts will be put in developing this PFAL to achieve higher productivity by balancing the resources consumption with the cloud-based control and monitor system.
Article
Plant factory, a new agricultural planting technology, has emerged and rapidly grown in recent years, with phosphor conversion light emitting diodes (pc-LEDs) considered as the first choice of source light for the plant factory. In this study, a new type of Cr³⁺-activated Li2MgTi3O8 phosphor (LMT: Cr³⁺) was synthesized by high temperature solid state method. X-Ray diffraction patterns showed that there was no detectable impurity in these samples. The photoluminescence spectra revealed that this phosphor can emit far-red light with the peak at 740 nm excited by ultraviolet and blue light, overlapped well with the PFR. After introducing Zn²⁺ ions (LMT: Cr³⁺, Zn²⁺), the luminescence intensity increases by 46% mainly due to the increase of lattice distortion, and internal quantum yield was improved from 25.4% to 41.3% under 365 nm excitation. Finally, the pc-LED devices, consisting of 470 nm chip coated with the optimal phosphor, exhibited good luminescence and overlapping with PFR. These results indicate that the LMT: Cr³⁺, Zn²⁺ phosphor has the potential application in modern agriculture.
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Vertical farming is considered as a potential solution to increase yield while decreasing resource use and pesticide impacts compared to conventional agriculture. However, the profitability of cultivating ordinary leafy green crops with low market prices in vertical farming is debated. We studied the agronomic feasibility and viability of growing a medicinal plant—Euphorbia peplus—for its ingenol-mebutate content in a modified shipping container farm as an alternative crop cultivation system. The impacts of three hydroponic substrates, three light intensities, three plant localizations and two surface areas on E. peplus yield and cost were tested in several scenarios. The optimization of biomass yield and area surface decreased the cultivation cost, with fresh crop cost per kg ranging from €185 to €59. Three ingenol-mebutate extraction methods were tested. The best extraction yields and cheapest method can both be attributed to ethyl acetate at 120 °C, with a yield of 43.8 mg/kg at a cost of €38 per mg. Modeling of the profitability of a pharmaceutical gel based on ingenol-mebutate showed that economic feasibility was difficult to reach, but some factors could rapidly increase the profitability of this production.
Article
The literature on agricultural technology (ag-tech) for urban agriculture (UA) offers many narratives about its benefits in addressing the challenges of sustainability and food security for urban environments. In this paper, we present a literature review for the period 2015–2022 of research carried out on currently active UA installations. We aim to systematise the most common narratives regarding the benefits of controlled environment agriculture (CEA) and soil-less growing systems in urban buildings and assess the existence of peer-reviewed data supporting these claims. The review was based on 29 articles that provided detailed information about 68 active UA installations depicting multiple types of ag-tech and regions. The results show that most research conducted for commercial UA-CEA installations was carried out in North America. Standalone CEA greenhouses or plant factories as commercial producers for urban areas were mostly found in Asia and Europe. The most often cited benefits are that the integration of multiple CEA technologies with energy systems or building climate systems enables the transfer of heat through thermal airflow exchange and CO2 fertilisation to improve commercial production. However, this review shows that the data quantifying the benefits are limited and, therefore, the exact environmental effects of CEA are undetermined.
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Uncertain climate changes and increasing energy and food production demands lead to food insecurity, especially for drought-prone areas like the study region, Iran. This study assesses the energy use, economic, and environmental impacts of two different healing and acclimatization systems, the conventional tunnel systems (CTS) and the LED-equipped vertical systems (LVS), for grafted watermelon seedlings in Iran. Life cycle assessment (LCA), cumulative exergy demand (CExD), and life cycle cost analysis (LCCA) approaches are used to assess the impacts of grafted watermelon seedlings. The functional unit is one million grafted watermelon seedlings (MGWS). The top findings of this study indicate that CTS increases energy consumption, damage to human health, ecosystems, and resources compared with the LVS. Further, the economic analysis revealed that the net profit in the multi-floored LVS is 24% higher than that of the CTS. In conclusion, LVS is less energy consumptive and environmentally burdensome yet more profitable than the CTS. Notably, the finding from this study supports recommendations that will be useful for industries or producers who need to develop sustainable grafted watermelon or vegetable production systems in Iran or similar regions. Top recommendations include using organic fertilizers, multi-floor LVS, and most importantly, replacing CTS with LVS to promote a sustainable agricultural production system.
Article
Indoor farming refers to a method of growing crops on vertically stacked layers in a soilless cultivation system (e.g., hydroponics) in a controlled indoor environment. In comparison with conventional open-field farms, indoor farming has advantages such as significantly improved productivity and water use efficiency, and reduction in food miles. However, indoor farming facilities are energy-intensive for maintaining favorable crop growing conditions. In this study, we evaluated the energy performance of indoor farming operations using both measurements and simulation results. Key performance parameters were first analyzed based on utility bills and continuous measurements from an indoor farming facility. Several operational issues were identified for the mechanical system. An energy model for an indoor farming facility was created using building energy simulation software EnergyPlus and calibrated based on measurements. A novel modeling approach simulating the unique mechanical system—misting systems—for indoor farming was developed using one of the advanced features in EnergyPlus— energy management system (EMS). The energy model was used to evaluate the effectiveness of energy-saving strategies to improve the energy efficiency of facility operations. These include simultaneous heating and cooling, hardly met temperature setpoints and improperly controlled dampers. These energy efficiency measures include fixing motorized damper control, eliminating simultaneous heating and cooling, and having wider ranges of temperature setpoints. Up to 48.1% of reduction in annual natural gas consumption was predicted with energy-saving measures. In addition, the limitations of using building energy simulation software for indoor farming modeling were discussed.
Article
This article addresses the lack of information for predicting the energy consumption of strawberry plantations inside plant factories located in tropical climate regions. This study aims to investigate the energy consumption of the cultivation of strawberries in the controlled environment room and to develop a TRNSYS computer model for the controlled environment room. Experiments were conducted in a 25 m3 controlled environment room. There are 180 strawberry trees inside the room. Light Emitting Diode (LED) grow light substitutes for natural sunlight. An air conditioner was used to regulate the indoor air condition. A computer model was developed using TRNSYS (TRaNsientSYStem simulation tool) and was validated using the collected data. There are three main components of the room heat load: transmission, lighting, and evapotranspiration. The lighting heat load shares more than 96% of the total heat load — the evapotranspiration load increases when the LED turns on. However, the lighting consumes only about 36% of total electricity consumption, while the air conditioner consumes 64%. Most of the electricity is used during the runner stage. Electricity consumption can be saved by 40% if the runners are grown outside the plant factory. Therefore, the high heat load is a feature in the plant factory. In this study, the lighting heat load is the most significant parameter. The strawberry light intensity requirement is the high lighting heat load. Consequently, the electricity for the air conditioner becomes high since the air conditioner removes the generated heat from the high light intensity. Therefore, the air conditioner electricity consumption is enormous in this study. Moreover, the required lighting intensity, photoperiod, and low air temperature factors affect electricity consumption. Therefore, the results from this study could provide strategies for energy cost reduction and plantation management for plant factories cultivation.
Thesis
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Population growth and urbanisation trends bring many consequences related to the increase in global energy consumption, CO2 emissions and a decrease in arable land per person. High‑rises have been one of the inevitable buildings of metropoles to provide extra floor space since the early examples in the 19th century. Therefore, optimisation of high-rise buildings has been the focus of researchers because of significant performance enhancement, mainly in energy consumption and generation. Based on the facts of the 21st century, optimising high-rise buildings for multiple vital resources (such as energy, food, and water) is necessary for a sustainable future. This research suggests “self-sufficient high-rise buildings” that can generate and efficiently consume vital resources in addition to dense habitation for sustainable living in metropoles. The complexity of self-sufficient high-rise building optimisation is more challenging than optimising regular high-rises that have not been addressed in the literature. The main challenge behind the research is the integration of multiple performance aspects of self-sufficiency related to the vital resources of human beings (energy, food, and water) and consideration of large numbers of design parameters related to these multiple performance aspects. Therefore, the dissertation presents a framework for performance optimisation of self-sufficient high-rise buildings using artificial intelligence focusing on the conceptual phase of the design process. The output of this dissertation supports decision-makers to suggest well-performing high-rise buildings involving the aspects of self sufficiency in a reasonable timeframe.
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The use of closed growth environments, such as greenhouses, plant factories, and vertical farms, represents a sustainable alternative for fresh food production. Closed plant production systems (CPPSs) allow growing of any plant variety, no matter the year’s season. Artificial lighting plays an essential role in CPPSs as it promotes growth by providing optimal conditions for plant development. Nevertheless, it is a model with a high demand for electricity, which is required for artificial radiation systems to enhance the developing plants. A high percentage (40% to 50%) of the costs in CPPSs point to artificial lighting systems. Due to this, lighting strategies are essential to improve sustainability and profitability in closed plant production systems. However, no tools have been applied in the literature to contribute to energy savings in LED-type artificial radiation systems through the configuration of light recipes (wavelengths combination. For CPPS to be cost-effective and sustainable, a pre-evaluation of energy consumption for plant cultivation must consider. Artificial intelligence (AI) methods integrated into the prediction crucial variables such as each input-variable light color or specific wavelengths like red, green, blue, and white along with light intensity (quantity), frequency (pulsed light), and duty cycle. This paper focuses on the feature-selection stage, in which a regression model is trained to predict energy consumption in LED lights with specific light recipes in CPPSs. This stage is critical because it identifies the most representative features for training the model, and the other stages depend on it. These tools can enable further in-depth analysis of the energy savings that can be obtained with light recipes and pulsed and continuous operation light modes in artificial LED lighting systems.
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Controlled environment agriculture (CEA) is expanding globally, but little is known about nutrient losses within these systems, or how to reduce subsequent pollution. This experiment investigates the potential to treat wastewater from hydroponically produced lettuce via the application of algae. A total of 132 heads of lettuce were produced in the 4‐layer nutrient film technique (NFT) vertical farming rack. Waste from the hydroponic system was used to cultivate naturally occurring algae. Nitrogen (N), phosphorus (P) and other trace elements (Ca, Co, Cu, Fe, K, Mg, Mn, Mo, Ni and Zn) were measured at each stage of production. Overall the nutrient use efficiency (NUE) of applied mineral nitrogen (N) and phosphorus (P) was 88.7% and 59.4%. After algae treatment of waste streams the full system NUE of N and P was 99.5% and 95.0% respectively, thus significantly reducing waste heading for sewage. It was found that the crops consumed large quantities of Ca, Cu, Fe and Zn from the rooting sponges used in this experiment, which may have become available due to mineralization and the presence of slightly acidic fertiliser solution. The overall waste produced by the rooting sponge is of concern regarding the full NUE of the system, accounting for approximately 53% and 6% of the total N and P input into the system. This study highlights that treating wastewater streams from controlled environment agriculture (CEA) methods such as hydroponics with algae is successful and easy to achieve with little effort. Future efforts by researchers and the CEA industry to better manage nutrient streams is recommended to improve the environmental credentials of developing CEA systems.
Chapter
This chapter starts with a classification of controlled environment agriculture types: rooftop greenhouses, façade farms and plant factories that utilise sunlight or rely solely on artificial lighting sources. When designing a viable scenario for the adaptive reuse of buildings for food production, an architect must make strategic decisions in the planning, architectural and environmental dimensions. The literature review on opportunities and limitations for repurposing urban structures for food production within these thematic categories is presented and summarised. Then these findings are applied to the three building-based farming operations. The case study reveals that the opportunities and limitations in the planning domain are similar for all types of controlled environment agriculture. However, the architectural and environmental analysis indicated a different potential to place food growing installations arising from specific attributes of the building.
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Since plants with a high biomass conversion efficiency of light energy consume less energy and require shorter cultivation periods, it is expected that plant factories can have more output with less energy. However, there have been few studies on the biomass conversion efficiency of light energy in various cultivated plants, and this agricultural engineering field is still unexplored. If the amount of energy consumed by a plant factory can be obtained from the biomass conversion efficiency of light energy, the plant types that can be grown in a plant factory and the economic efficiency of the plant factory can be clarified. In this study, we determined the amount of light energy required for plant cultivation by measuring the wavelength distribution of sunlight and plant-growing light-emitting diodes. Also, we investigated the light to biomass conversion efficiency from the amount of heat generated by the biomass of cultivated plants. The light to biomass conversion efficiency was also used to analyze the payback period of plant factories so as to estimate the profitability of various cultivated plants. The solar to biomass conversion efficiency of the tested leafy vegetables ranged from 0.03% to 0.62%, while the efficiency of the cultivation LEDs ranged from 1.21% to 20.1%. The conversion efficiency including the energy consumption of air conditioning ranged from 0.13 to 5.7%. By measuring the biomass conversion efficiency of plants, it is possible to analyze the profitability of plant factories with a high degree of accuracy.
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The development in solar PV technology is growing very fast in recent years due to technological improvement, cost reductions in materials and government support for renewable energy based electricity production. Photovoltaic is playing an important role to utilize solar energy for electricity production worldwide. At present, the PV market is growing rapidly with worldwide around 23.5 GW in 2010 and also growing at an annual rate of 35-40%, which makes photovoltaic as one of the fastest growing industries. The efficiency of solar cell is one of the important parameter in order to establish this technology in the market. Presently, extensive research work is going for efficiency improvement of solar cells for commercial use. The efficiency of monocrystalline silicon solar cell has showed very good improvement year by year. It starts with only 15% in 1950s and then increase to 17% in 19705 and continuously increase up to 28% nowadays. The growth in solar photovoltaic technologies including worldwide status, materials for solar cells, efficiency, factor affecting the performance of PV module, overview on cost analysis of PV and its environmental impact are reviewed in this paper.
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'Ostinata' Butterhead lettuce (Lactuca sativa L.) was used to study lettuce production at varied shoot (air) and root (pond) temperatures. A floating hydroponic system was used to study the influence of pond temperature on lettuce growth for 35 days. Pond water temperature setpoints of 17, 24, and 31 °C were used at air temperatures of 17/12, 24/19, and 31/26 °C (day/night). Pond temperature affected plant dry mass, and air temperature significantly affected growth over time. Maximum dry mass was produced at the 24/24 °C (air/pond temperature) treatment. Final dry mass at the 31/ 24 °C treatment did not differ significantly from the 24/24 °C treatment. The 24 °C pond treatment maintained market quality lettuce head production in 31 °C air. Using optimal pond temperature, lettuce production was deemed acceptable at a variety of air temperatures outside the normal range, and particularly at high air temperatures.
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We measured electric energy consumption and estimated electric energy cost of a closed-type transplant production system to investigate how much we can reduce them toward a practical use of the closed-type transplant production system. Sweetpotato (Ipomoea batatas (L.) Lam. cv. Beniazuma) transplants were grown for 15 days under 31/42/68W m-2 (1-5/6-10/11-15 days after planting, respectively) photosynthetic active radiation with 16h d-1 photoperiod, 28°C air temperature, 75% relative humidity and 920μmol mol-1 CO2 concentration in the closed-type transplant production system. The amounts of electric energy consumption of lamps, air conditioners, fans and humidifiers during 15 days were 376, 118, 55 and 19 MJ m-2, respectively. The amount of increased chemical energy of transplants was 3 MJ m-2. The electric energy cost per tray of the closed-type transplant production system was estimated as 288 Yen. We estimated reductions of 50% of electric energy consumption of lamps, 20% of air conditioners, 40% of fans, 30% of humidifiers and 7% of electric energy cost without reducing the amount of increased chemical energy of transplants during 15 days by improving the efficiency of lighting, air cooling and circulating systems. From the above estimation, the amount of electric energy consumption and the electric energy cost per tray of the improved closed-type transplant production system will be 288MJ m-2 (50% reduction) and 132 Yen (54% reduction).
Conference Paper
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Plant factories with artificial light (PFALs) are gradually accepted for plant production in Asian countries, such as Japan, China and Korea. It is essential to use artificial light for plant production in a PFAL with opaque materials for the walls. Heat pumps are often used to remove extra heat generated especially by lamps to maintain an optimum air temperature. The cost of electric-energy consumed by lamps and heat pumps in a PFAL is high and the commercial use of PFAL is therefore limited. The objectives of this study were to analyze possible solutions for improving the electric-energy utilization efficiencies (EUE) by investigating those of fluorescent lamps and heat pumps as affected by the air temperature, etc. A PFAL with a volume of 1,429 m3 located in Chiba, Japan with lettuce plants was used in this study. The results show that the EUE of the lamps, defined as ratio of fresh weight of lettuce to photosynthetic active radiation emitted, ranged from 0.9 to 34.9 g mol -1 and increased with plant growth. The system coefficient of performance (COP) for cooling of the heat pumps ranged from 3.5 to 6.6 when the indoor air temperature was kept at about 21°C and outdoor air temperature ranged between -7.3°C and 25.8°C. The COP increased with increasing indoor-outdoor air temperature difference and decreasing vapor pressure deficit. Based on the above analysis, possible solutions for improving the EUE in a PFAL are given in this paper to reduce the electric-energy consumption and running costs of a PFAL.
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A 'closed plant production system' or simply a 'closed system' is defined in this article as a warehouse-like structure covered with opaque thermal insulators, in which ventilation is kept at a minimum, and artificial light is used as the sole light source for plant growth. Advantages of a closed system over a greenhouse for production of plants less than 30 mm in height include: 1) rapid and uniform growth of high quality plants, 2) high productivity per floor area partly due to the use of multi-shelves, 3) high utilization efficiencies of water and CO2 due to the minimized ventilation and recycling uses of water and CO2, 4) high light utilization efficiency of plants due to optimized temperature, PPF, CO2 concentration and water content of the substrate, and 5) virtually no heating cost requirement in winter even in northern countries due to its thermally insulated structure. Initial and operation costs per plant in closed systems are comparable to those in greenhouses. In 2005, the closed systems are used at 30 different locations in Japan for commercial production of transplants, herbal/medicinal plants and leafy vegetables, and at 10 different locations for research purposes.
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Extensive research has recently been conducted on plant factory with artificial light, which is one type of closed plant production system (CPPS) consisting of a thermally insulated and airtight structure, a multi-tier system with lighting devices, air conditioners and fans, a CO2 supply unit, a nutrient solution supply unit, and an environment control unit. One of the research outcomes is the concept of resource use efficiency (RUE) of CPPS. This paper reviews the characteristics of the CPPS compared with those of the greenhouse, mainly from the viewpoint of RUE, which is defined as the ratio of the amount of the resource fixed or held in plants to the amount of the resource supplied to the CPPS. It is shown that the use efficiencies of water, CO2 and light energy are considerably higher in the CPPS than those in the greenhouse. On the other hand, there is much more room for improving the light and electric energy use efficiencies of CPPS. Challenging issues for CPPS and RUE are also discussed.
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Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves. These aspects include the kinetic properties of ribulose bisphosphate carboxylase-oxygenase; the requirements of the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles for reduced pyridine nucleotides; the dependence of electron transport on photon flux and the presence of a temperature dependent upper limit to electron transport. The measurements of gas exchange with which the model outputs may be compared include those of the temperature and partial pressure of CO2(p(CO2)) dependencies of quantum yield, the variation of compensation point with temperature and partial pressure of O2(p(O2)), the dependence of net CO2 assimilation rate on p(CO2) and irradiance, and the influence of p(CO2) and irradiance on the temperature dependence of assimilation rate.
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Lettuce (Lactuca sativa) production historically has been limited in the southeastern United States because of the risk of early bolting and unacceptable bitterness. Small-scale vegetable growers may be able to include lettuce in their production through selection of bolt tolerant and nonbitter varieties. The objectives of this research were to evaluate earliness, bitterness, vitamin E, ascorbic acid, folate, β-carotene, and lutein content in 17 lettuce varieties. Significant difference were found among varieties for days to harvest (DTH) (47 DTH for 'Epic' to 37 DTH for 'Big Curly'). Observed DTH in this study was consistently 7 to 10 days less than commercial descriptions of the lettuce varieties, due to the use of transplants. Only 'Slobolt' and 'Greengo' bolted before reaching marketable size. Panelists found that the bitterness was acceptable for most varieties, but not for 'Nancy,' 'Big Curly,' and 'Slobolt'. Significant differences among varieties were also found in vitamin E, ascorbic acid, folate, β-carotene, and lutein. 'Redprize' and 'Nevada' were the best varieties overall, while 'Salinas 88 Supreme,' 'Epic,' 'Legacy,' 'Big Curly,' 'Slobolt,' and 'Greengo' were unacceptable.
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Many of the popular building energy simulation programs around the world are reaching maturity — some use simulation methods (and even code) that originated in the 1960s. For more than two decades, the US government supported development of two hourly building energy simulation programs, BLAST and DOE-2. Designed in the days of mainframe computers, expanding their capabilities further has become difficult, time-consuming, and expensive. At the same time, the 30 years have seen significant advances in analysis and computational methods and power — providing an opportunity for significant improvement in these tools.In 1996, a US federal agency began developing a new building energy simulation tool, EnergyPlus, building on development experience with two existing programs: DOE-2 and BLAST. EnergyPlus includes a number of innovative simulation features — such as variable time steps, user-configurable modular systems that are integrated with a heat and mass balance-based zone simulation — and input and output data structures tailored to facilitate third party module and interface development. Other planned simulation capabilities include multizone airflow, and electric power and solar thermal and photovoltaic simulation. Beta testing of EnergyPlus began in late 1999 and the first release is scheduled for early 2001.
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A central challenge for sustainability is how to preserve forest ecosystems and the services that they provide us while enhancing food production. This challenge for developing countries confronts the force of economic globalization, which seeks cropland that is shrinking in availability and triggers deforestation. Four mechanisms-the displacement, rebound, cascade, and remittance effects-that are amplified by economic globalization accelerate land conversion. A few developing countries have managed a land use transition over the recent decades that simultaneously increased their forest cover and agricultural production. These countries have relied on various mixes of agricultural intensification, land use zoning, forest protection, increased reliance on imported food and wood products, the creation of off-farm jobs, foreign capital investments, and remittances. Sound policies and innovations can therefore reconcile forest preservation with food production. Globalization can be harnessed to increase land use efficiency rather than leading to uncontrolled land use expansion. To do so, land systems should be understood and modeled as open systems with large flows of goods, people, and capital that connect local land use with global-scale factors.
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The productivity of lettuce in a combination of high light, high temperature, and elevated CO2 has not been commonly studied because rapid growth usually causes a calcium deficiency in meristems called tipburn, which greatly reduces quality and marketability. We eliminated tipburn by blowing air directly onto the meristem, which allowed us to increase the photosynthetic photon flux (PPF) to 1000 micromoles m-2 s-1 (57.6 mol m-2 d-1); two to three times higher than normally used for lettuce. Eliminating tipburn doubled edible yield at the highest PPF level. In addition to high PPF, CO2 was elevated to 1200 micromoles m-2 mol-1, which increased the temperature optimum from 25 to 30 degrees C. The higher temperature increased leaf expansion rate, which improved radiation capture and more than doubled yield. Photosynthetic efficiency, measured as canopy quantum yield in a whole-plant gas exchange system, steadily increased up to the highest temperature of 32 degrees C in high CO2. The highest productivity was 19 g m-2 d-1 of dry biomass (380 g d-1 fresh mass) averaged over the 23 days the plants received light. Without the limitation of tipburn, the combination of high PPF, high temperature, and elevated CO2 resulted in a 4-fold increase in growth rate over productivity in conventional environments.
Article
Population growth and rapid urbanisation may result in a shortage of food supplies for cities in the foreseeable future. Research on closed plant production systems, such as plant factories, has attempted to offer perspectives for robust (urban) agricultural systems. Insight into the explicit role of plant processes in the total energy balance of these production systems is required to determine their potential. We describe a crop transpiration model that is able to determine the relation between sensible and latent heat exchange, as well as the corresponding vapour flux for the production of lettuce in closed systems. Subsequently, this model is validated for the effect of photosynthetic photon flux, cultivation area cover and air humidity on lettuce transpiration, using literature research and experiments. Results demonstrate that the transpiration rate was accurately simulated for the aforementioned effects. Thereafter we quantify and discuss the energy productivity of a standardised plant factory and illustrate the importance of transpiration as a design parameter for climatisation. Our model can provide a greater insight into the energetic expenditure and performance of closed systems. Consequently, it can provide a starting point for determining the viability and optimisation of plant factories.
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Annual energy consumption and carbon footprints are compared in simulation for two controlled environments: plant factory and traditional greenhouse. Energy consumed for heating, ventilating, and air conditioning (HVAC) as well as supplemental lighting are included in the models. In the greenhouse case, supplemental lighting is controlled to a consistent daily light integral (DLI) of Photosynthetically Active Radiation (PAR) using Light and Shade System Implementation (LASSI). In the plant factory model, lighting power is sized according to photoperiod and DLI requirements. Building HVAC loads and system responses are computed using the ASHRAE heat balance method with a one hour time-step. Both environments are simulated in four different climates using Typical Meteorological Year (TMY) data sets. In each simulation, energy consumption and carbon footprints are shown to be significantly higher in the plant factory environment compared to the greenhouse.
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The effects of three irradiances and four rootzone temperatures on the growth and photosynthesis of three cultivars of Lactuca sativa L. (a temperate plant) 'Armada', 'Olympia', and 'Palma' were studied using aeroponic systems under warm aerial temperatures. The rootzone temperatures were controlled at 15°C, 20°C and 25°C. The control rootzone was subjected to diurnal temperatures which ranged from 28°C to 39°C during the day. Plants exposed to different rootzone temperatures were grown under three light regimes in a greenhouse: 100%, 70% and 40% of prevailing solar radiation with maximum midday irradiances of ca. 1800, 1250 and 720 μmol photons m-2 s-1 respectively on sunny days. For all three cultivars grown under different rootzone temperatures, photosynthetic rates decreased as irradiances decreased. Regardless of irradiance, maximum photosynthetic rates were much lower in the control plants than in plants grown with rootzones at lower temperatures. However, no significant difference in maximum photosynthetic rates was observed among those plants with rootzones exposed to the lower temperatures (15°C, 20°C and 25°C) under the same growth irradiance. Both rootzone temperatures and growth irradiance affected the growth and development of root and shoot (the formation of compact heads) of all three cultivars. Interaction of rootzone temperature and growth irradiance on the growth of shoot and root and photosynthesis are discussed with particular emphasis on the optimum conditions for growing temperate plants such as Lactuca sativa L. in the tropics.
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Five cultivars of leaf lettuce (Lactuca sativa L. var. crispa) - Bergamo, Dubáček, Frisby, Lollo Rossa and Redin - were evaluated in two-year experiments carried out at the Faculty of Horticulture in Lednice (Mendel University of Agriculture and Forestry in Brno). Experiments were conducted in two trial years, 1998 and 1999; the lettuce was cultivated in three seasons: spring, summer and autumn. After the harvest, contents of following nutrients were evaluated: vitamin C, minerals (K, Na, Ca, Mg), fibre, dry matter and nitrates. The weight of leaf rosette was also recorded. The contents of selected substances and weights of leaf rosette were ranged as follows: vitamin C (65 to 302 mg/kg), potassium (2,394 to 6,477 mg/kg), sodium (39 to 223 mg/kg), calcium (200 to 755 mg/kg), magnesium (110 to 413 mg/kg), fibre (4.98 to 12.22 g/kg), dry matter (59 to 140 g/kg), nitrates (293 to 3,817 mg/kg) and the weight of leaf rosette (164 to 502 g). A significant influence of cultivar was found in the case of K, Na, and Ca content, as well as in dry matter and weight of leaf rosette. The growing season affected significantly all the evaluated substances, except for fibre. The year of cultivation affected all the evaluated parameters but Ca. It appears from the results that the contents of monitored substances were significantly influenced by cultivar as well as by growing season and year.
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Plant factories where leafy vegetables are cultivated until harvest in closed systems with artificial lighting were proposed, developed, and implemented in Japan during the 1980s. During the 1990s, the products from these factories received high evaluations by the food service industry, to which they primarily catered. During the 2000s, commercial production of nursery plants of fruits and vegetables was initiated in plant factories. Since the late 2000s, plant factory technology has been introduced worldwide, particularly to Asian countries. Plant factories also provide good cultivation systems for the production of medicinal plants and genetically modified crops for pharmaceutical use. In late 2000s, light-emitting diodes (LEDs) were introduced to plant factories as a more efficient light source. LEDs are expected to reduce the electricity costs of lighting and cooling because they have a higher efficiency of converting electric power to light power and exert lower cooling loads than conventional light sources. To achieve plant production in plant factories by using LEDs, more achievement of plant research is required taking engineering and plant physiological approaches, in areas such as the creation of optimal LED lighting systems, promotion of photosynthesis, control of gene expression, photomorphogenesis, and synthesis of secondary metabolites. This study reviews recent research status and achievements regarding plant production in plant factories with artificial lighting and introduces plant research topics related to LEDs utilization.
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This paper reviews the reasons why plant factories with artificial light are recently interested in society, requirements for sustainable plant factories, the opportunities and challenges involved in the development of the technology and industry, and types of the plants suitable for plant factories with artificial light. Sustainable plant factories need to be designed and operated for producing high quality plants and transplants with minimum use of resource and minimum emissions of CO2 and environmental pollutants. For this purpose, the concept of "closed system" has been proposed, which is a structure with minimum ventilation, covered with thermally insulated opaque walls, containing multi-tiers (or racks) with artificial light sources. Advantages of this system over the greenhouse include: 1) culture period is shortened by 40-50% with uniform growth and high quality produce, 2) annual production capacity per floor area is 100-fold, and 3) percent reductions in resource consumption are considerable. For example, percent reduction is 100% for pesticide and 95% for irrigation water. Electricity consumption for producing one tomato transplant from a seed is about 300-400 kJ and its cost in Japan is about 1 JPY (0.008 Euro or 1 US cent as of 2011), and is 25 JPY for producing one butter head lettuce from a seed. Methods of developing integrative environmental control and reducing electricity consumption are discussed based mainly on theoretical consideration. Effects of environmental factors on the growth and development are beyond the scope of this paper.
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A series of experiments was undertaken to study daylength-mediated control of transition to flowering in lettuce (Lactuca sativa L.), a quantitative long-day plant. Several genotypes (cultivars, landraces, and mutant lines) were grown at different photoperiods, sometimes in combination with different temperatures, and measured for number of days to either a) bolting initiation (a detectable increase in the rate of stem elongation) or b) anthesis of the first flower (a standard measure of maturity in lettuce). Experiments were conducted in controlled or partially controlled environments. Results of these studies indicate the following: a) high temperature alone is not sufficient to induce the bolting response, whereas photoperiod is; b) there is a range of genetic responses to various daylengths among lettuce genotypes; c) one of the genes known to control bolting initiation, gene Z', exhibited reverse dominance in conjunction with the Early Flowering genes, depending on the length of day. The latter observation implies the genetic role of T needs further investigation, as it does not appear to operate by simple dominance alone.
Article
High tunnels have been shown to be a profitable season-extending production tool for many horticultural crops. Production of cool-season vegetables during the hot summer months represents a challenge to market growers in the midwestern United States. Two experiments were conducted to investigate the microclimate and production of eight leaf lettuce (Lactuca sativa) cultivars in high tunnels and open fields, using unshaded and shaded (39% white shadecloth) tunnels in Summer 2002 and 2003, respectively. Wind speed was consistently lower in high tunnels with the sidewalls and endwalls open. An unshaded high tunnel resulted in an increase of daily maximum and minimum air temperatures by ≈0.2 and 0.3°C respectively, in comparison with the open field. In contrast, daily maximum air temperature in a shaded high tunnel decreased by 0.4°C, while the daily minimum air temperature was higher than that in the open field by 0.5°C. Using high tunnels did not cause a marked change in relative humidity compared with the open field. When using shadecloth, the daily maximum soil temperature was lowered by ≈ 3.4 °C and the leaf surface temperature was reduced by 1.5 to 2.5°C. The performance of lettuce during summer trials varied significantly among cultivars. Unshaded high tunnels generally led to more rapid bolting and increased bitterness of lettuce compared with the open field. Lettuce grown in high tunnels covered by shadecloth had a lower bolting rate, but decreased yield relative to the open field. Based on our results, summer lettuce production would not be recommended in high tunnels or open fields in northeastern Kansas, although the potential of shaded high tunnels deserves further studies. Reference crop evapotranspiration (ET 0) was estimated from meteorological data on a daily basis using the FAO-56 method. The ET0 was lowest in the shaded high tunnel and was the highest in the open field. Relatively lower ET0 in high tunnels indicated a likely lower water requirement and therefore improved water use efficiency compared with the open field.
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Anyone who clicks on the link until June 14, 2015, will be taken to the final version for free http://authors.elsevier.com/a/1Qwhb1M27RQOGL We explore an under-appreciated side effect of semi-closed greenhouses: the ability to recover transpired water, thereby increasing water use efficiency. Semi-closed greenhouses are fit with cooling equipment, to limit natural ventilation requirements for temperature and humidity control. We assess the effect of cooling system capacity on ventilation needs of semi-closed greenhouses under different climate conditions and provide a general framework to evaluate potential water savings using the semi-closed greenhouse concept in different regions. We simulate greenhouse climate and crop yields for various cooling system capacities in Central Europe (The Netherlands) and Mediterranean (Greece and Algeria) by implementing a “cooling module” into an existing greenhouse model (KASPRO) and validating it using concurrent experimental data. Increasing the capacity of the cooling system has a double effect on water use efficiency (WUE): increase of fruit yield due to improved microclimate and lower water use, due to collection and reuse of vapour condensed in the heat exchanger and, to a lesser extent, lower crop transpiration. Thus WUE is strongly associated to the capacity of the cooling system. Finally, we show that there is a unique relationship between water use efficiency and the coupling of greenhouse environment to the outside air (an indicator of ventilation requirements), for all regions studied.
Article
Greenhouse crop production in semi-arid climates is desirable because high solar radiation levels are consistent year round. The use of evaporative cooling will further increase yields and crop consistency. However, these regions typically receive less than 500 mm of rain annually, making water use management a critical concern. This study evaluated water use for irrigation (WU I) and pad-and-fan (WU PF) evaporative cooling systems in a single-span, polyethylene-covered greenhouse in Tucson, Arizona, from March to October 2006. A single-use, non-recirculating irrigation system delivered water to hydroponically grown tomatoes. The pad-and-fan system was computer controlled to maintain day/night air temperatures of 24°C/18°C. The total eight-month WU I and WU PF were 780 and 1450 L m -2, respectively. WU I increased steadily from 4.3 L m -2 d -1 during crop establishment to 7.2 L m -2 d -1 when the plants were mature. WU PF increased from 1.1 L m -2 d -1 during early spring to a peak of 11 L m -2 d -1 during the hottest, driest outside conditions. The water use efficiency (WUE, kg yield per m 3 water use) of the irrigation and pad-and-fan cooling systems was 30 and 16 kg m -3, respectively. When WUE was calculated by combining WU I and WU PF, the total greenhouse WUE was 11 kg m -3. Theoretically, using a 100% recirculating irrigation system could have produced a greenhouse WUE of 13 kg m -3. This study demonstrates that although greenhouses achieve high annual yields with low irrigation rates, using an evaporative cooling system reduces greenhouse WUE to field WUE levels. To minimize greenhouse water use while maintaining high crop yields, this study recommends further examination of the use of recirculating irrigation systems, variable-speed fans to improve climate control, alternative cooling systems, and drought-tolerant crops. © 2011 American Society of Agricultural and Biological Engineers.
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Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since July 2014 are reviewed. Copyright © 2014 John Wiley & Sons, Ltd.
Article
Growth and photosynthetic characteristics were studied in lettuce (Lactuca sativa L.) cultured in an aeroponic system at two different times of the year. Midday ambient and leaf temperatures recorded in January were significantly lower than those measured in June. When the aerial parts were grown under hot ambient temperature but with their root zones exposed to 20°C, photosynthetic capacity and productivity were, respectively, about 20% and 30% higher measured from the leaves grown in January as compared with those planted in June. However, photosynthetic rate and productivity decreased by more than 50% at both periods when the whole plants were grown under hot ambient temperature as compared with those with their shoots maintained at hot ambient temperature but with their root zones exposed to a cool temperature of 20°C. There was no difference in quantum yield of photosynthetic O2 evolution and PS II efficiency (chlorophyll fluorescence Fv/Fm ratio) measured from leaves of those plants grown at both periods with their roots exposed to 20°C while decreases in these two parameters were observed when the whole plants were grown under hot ambient temperature, indicating photoinhibition.
Article
A field experiment was carried out to analyse the growth of lettuce, onion and red beet in terms of: ( a ) canopy architecture, radiation interception and absorption; ( b ) efficiency of conversion of absorbed radiation into biomass; and ( c ) dry matter partitioning. Growth analysis, total solar radiation interception, PAR interception and absorption by the crop canopy, ground cover, maintenance respiration of onion bulbs and red beet storage roots were measured. Models for different leaf angle distribution and ground cover were used to simulate light transmission by the crop canopy. The three crops are shown to have contrasting growth patterns from both a morphological and a physiological point of view. Lettuce showed very high light interception and growth after the early growth stages but, throughout the growth cycle, this leafy crop showed the lowest radiation use efficiency due to the respirational cost of the high leaf area. Onion showed a lower early relative growth rate than lettuce and red beet. This was due partly to the low light interception per unit leaf area in the later stages of growth and partly to the low initial radiation use efficiency compared with the other two crops. On the other hand, thanks to more uniform distribution of the radiation inside the canopy, to the earlier termination of leaf development and to the very low level of bulb respiration, onion showed high radiation use efficiency and was able to produce a large amount of dry matter. Red beet leaf posture and canopy structure resulted in high light interception and absorption. Its radiation use efficiency was lower than that of onion, partly perhaps because of the more adverse distribution of the intercepted radiation fluxes within the canopy and partly because of the high respiration cost of a continuous dry-matter allocation to the leaves. However, this crop can accumulate a very large amount of dry matter as leaf blade development and storage root growth can both continue almost indefinitely, providing continuously available sinks. Ground cover gave a good estimate of the PAR interception only at low values of light interception but, in general, it underestimated PAR interception in all three crops. Ratios between attenuation coefficients established by considering PAR or total solar radiation and LAI or ground cover were calculated.
Article
Low exergy (LowEx) building systems create more flexibility and generate new possibilities for the design of high performance buildings. Instead of maximizing the barrier between buildings and the environment using thick insulation, low exergy systems maximize the connection to the freely available dispersed energy in the environment. We present implementations of LowEx technologies in prototypes, pilots and simulations, including experimental evaluation of our new hybrid PV-thermal (PV/T) panel, operation of integrated systems in an ongoing pilot building project, and cost and performance models along with dynamic simulation of our systems based on our current office renovation project. The exploitation of what we call ”anergy sources” reduces exergy use, and thus primary energy demand. LowEx systems provide many heating and cooling methods for buildings using moderate supply temperatures and heat pumps that exploit more valuable anergy sources. Our implementation of integrated LowEx systems maintains low temperature-lifts, which can drastically increase heat pump performance from the typical COP range of 3–6 to values ranging from 6 to 13.
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Data from urban metabolism studies from eight metropolitan regions across five continents, conducted in various years since 1965, are assembled in consistent units and compared. Together with studies of water, materials, energy, and nutrient flows from additional cities, the comparison provides insights into the changing metabolism of cities. Most cities studied exhibit increasing per capita metabolism with respect to water, wastewater, energy, and materials, although one city showed increasing efficiency for energy and water over the 1990s. Changes in solid waste streams and air pollutant emissions are mixed.The review also identifies metabolic processes that threaten the sustainability of cities. These include altered ground water levels, exhaustion of local materials, accumulation of toxic materials, summer heat islands, and irregular accumulation of nutrients. Beyond concerns over the sheer magnitudes of resource flows into cities, an understanding of these accumulation or storage processes in the urban metabolism is critical. Growth, which is inherently part of metabolism, causes changes in water stored in urban aquifers, materials in the building stock, heat stored in the urban canopy layer, and potentially useful nutrients in urban waste dumps.Practical reasons exist for understanding urban metabolism. The vitality of cities depends on spatial relationships with surrounding hinterlands and global resource webs. Increasing metabolism implies greater loss of farmland, forests, and species diversity; plus more traffic and more pollution. Urban policy makers should consider to what extent their nearest resources are close to exhaustion and, if necessary, appropriate strategies to slow exploitation. It is apparent from this review that metabolism data have been established for only a few cities worldwide, and interpretation issues exist due to lack of common conventions. Further urban metabolism studies are required.
Article
A model of leaf photosynthesis and repiration was developed which adequately predicted carbon dioxide assimilation responses by a C 3 species, Atriplex patula, to light, [CO2], [O2] and temperature in controlled environments. Methods were developed for estimating input parameters using laboratory, controlled environment and field data.
Article
Resistance to early flowering is an important attribute of lettuce cultivars adapted to tropical conditions. Lettuce cultivars may vary widely in the number of days necessary from sowing to inflorescence formation and flowering. In this paper, we report on the polygenic inheritance of the number of days to flowering in two crosses among contrasting lettuce cultivars – Vitória × Brasil-303 and Babá × Elisa. F1 and F2 seed were obtained for each cross, and used to estimate broad sense heritabilities. F3 families were obtained from randonly sampled F2 plants, and used to estimate narrow sense heritabilities based on parent-offspring regression. Trials were carried out in plastic greenhouses in Campos dos Goytacazes, in the Northern part of the State of Rio de Janeiro, Brazil. Broad and narrow sense heritabilities for days to first anthesis were 0.737 and 0.489 for the cross Vitória × Brasil-303, and 0.818 and 0.481 respectively, for the cross Babá × Elisa. In both crosses, both early and late-flowering transgressive segregants were obtained. Genetic gains based on selection of late flowering transgressive segregants in the F2's were estimated to be 10.2 days in Vitória × Brasil-303 cross, and 8.7 days in the Babá × Elisa cross.
Article
Adaptation of greenhouse climate management strategy to local climatic conditions is very important for the improvement of resource use efficiency of greenhouse crop production. The objective of this study was to explore alternatives to the existing Venlo-type greenhouse climate control policy under Chinese subtropical climate conditions, through simulation analysis using the Greenhouse Process (KASPRO) model. Experiments were carried out in a Dutch Venlo-type glasshouse on a farm in Shanghai (31·3 °N, 121·4 °E), to collect climate and crop data to validate the model. The results show that using outside hourly weather data as inputs, the KASPRO model generally gives satisfactory predictions of greenhouse air temperature and humidity, and of canopy transpiration rate under both summer and winter climate conditions for subtropical China. After the model validation, scenario studies were carried out to investigate the possible responses of crop biomass production and energy consumption to different nighttime and daytime air temperature set points and canopy size based on leaf area index (LAI), under the winter climate conditions typical of subtropical China. The scenario analysis shows that, during winter, the highest biomass production is achieved when the daily mean air temperature in the greenhouse is 19·7 °C, which is realised when day and night air temperature set points are 23 and 18 °C, respectively. The highest energy use efficiency for biomass production is achieved when daily mean air temperature in the greenhouse is 18 °C, which is realised by setting the set points of air temperature at 19 and 15 °C, respectively. During winter, crop biomass production reaches the maximum at a LAI of 3. The energy consumption increases with the canopy LAI. It is concluded that both from the biomass production and energy saving point of view, an air temperature set point of 19 °C for daytime and 15 °C for nighttime and a canopy LAI of 2–3 provides the most energy-efficient conditions for greenhouse cucumber crop production under the winter climate conditions in subtropical China.
Article
Adaptation of a greenhouse climate management strategy to local climate conditions is important for the improvement of resource use efficiency of greenhouse crop production. In this paper the optimal greenhouse climate management under hot, humid, subtropical summer conditions was investigated through simulation analysis based on the Greenhouse Process (KASPRO) model, previously validated under this particular conditions. The study was limited to affordable means of greenhouse design, crop and climate management such as ventilation capacity, canopy size and whitewashing, in a greenhouse without injection of carbon dioxide. Obviously, the increase of greenhouse ventilation capacity leads to an increase of carbon dioxide concentration in the greenhouse air, canopy transpiration, and thus evaporative cooling of the greenhouse air and crop canopy, and in turn to an increase of crop biomass production. The results show, however, that there is a rather sharp ceiling beyond which there is little gain in increasing ventilation capacity. For a cucumber crop under the summer conditions typical of Shanghai, the ventilation capacity of the greenhouse should be about 40 volume changes per hour. The balance of assimilation, respiration and evaporative cooling ensure that crop biomass production is maximal at a canopy leaf area index of 4.
Article
An integrated ecological approach to agricultural production, urban planning and food policy-making is examined in respect of the agricultural zone peripheral to large urban settlements. It is asserted that intensive agriculture at the urban-rural interface can reduce reliance on food imports from other countries, provide employment opportunities, recycle valuable urban and agricultural wastes back into the human food chain and maintain environmental amenity for the human population. The ecosystem approach to urban fringe agriculture is examined in the context of Hong Kong, a city of 4·5 million people. It is hypothesised that intensive agriculture in Hong Kong, developed in the ways specified, can provide a model for ecological management of the urban-rural interface for urban settlements in general.
Article
"Stellingen" inserted. Thesis (doctoral)--Landbouwuniversitet te Wageningen, 1996. Includes bibliographical references (p. 171-174).
Article
The overall design of an industrial crop production system should optimize the system's global parameters, such as total area required, intensity of cultivation and general production schedule. The key element is the optimal intensity of cultivation for the prevailing climatic and economic environments. A single-state-variable vegetative crop model (e.g. lettuce) was used to optimize a crop production system for two economic environments: quota- and area-limited production. A strictly uniform weather (every hour of the season) was assumed initially. Continuous spacing was a central control element. The main conclusions of the analysis with our model are: (1) plants of all ages can grow together in a single climatic compartment; (2) spacing should be scheduled to maintain a constant canopy density; (3) optimal canopy density is an increasing function of available light and a decreasing function of temperature; (4) where produce-price is high relative to the prices of rent and energy, the optimal cultivation intensity for an area-limited operation is higher than for a quota-limited operation; the opposite is true where rent is expensive; and (5) the marginal price to be paid for supplementary light is smaller where available natural light is more plentiful.