Protected Cropping in Warm Climates: A Review of Humidity Control and Cooling Methods

Analysis of dataset on reduction of high temperature stress by green net shade alleviate oxidative stress and augments the growth and vase life of gladiolus cut flower

The study was conducted to investigate the effect of green net shade during staggered planting times on growth, biochemical, antioxidant enzymes and vase life of gladiolus cut flowers. The green net shade effectively reduces the internal temperature, particularly during extremely hot planting times. Under the green net shade conditions, high quality morphological and biochemical observations were observed during the months of March and April planting times. These included longer plant height, spike length, a higher number of leaves plant-1, larger leaf area, maximum spike diameter, greater number of florets spike-1, heavier flower diameter, higher fresh and dry weight, elevated photosynthetic rate, and reduced time taken for flowering. Additionally, chlorophyll contents and transpiration rate showed significant increases, while antioxidant enzyme activity (POD and CAT) was recorded at higher levels. This resulted in reduced electrolyte leakage and an extended vase life of the gladiolus cut flowers. Moreover, the application of green net shade conditions during the planting in May and June significantly enhanced the quality characteristics of gladiolus cut flowers. Effectiveness of green net shade is evident in reducing temperature of growing environment, leading to improved growth, alleviate oxidative stress, enhanced quality features and vase life of the gladiolus flowers.

Field investigation of non-uniform environment in a Venlo-type greenhouse in Yangling, China

Non-uniform environmental conditioning has established substantial energy-saving and conditioning effects in residential buildings, however, few studies on the technology applied in greenhouses have been conducted. Semi-enclosed greenhouse development is hindered by energy consumption. To better apply non-uniform environmental conditioning technology in greenhouses, it is necessary to investigate the non-uniform characteristics of field environment parameters. Therefore, spatial and temporal measurements of indoor temperature and relative humidity in a Venlo-type greenhouse in Yangling, China, were conducted on June 5-11, 2022. Temperature and humidity sensors were arranged in the greenhouse at 4.5 m intervals, in the canopy, cultivation, center, and root areas. Temperature and humidity measurement points on the greenhouse walls were selected. The measurement results showed large fluctuations in the indoor temperature and relative humidity over time. The difference between indoor and outdoor average temperatures ranged from -5-10 °C and temperatures unsuitable for tomato growth were identified, although some passive conditioning methods such as ventilation and water spraying were employed, which indicates the necessity of active heating and cooling. Based on the measured data, the nonuniformity coefficients of temperature and relative humidity in different directions in the greenhouse were calculated. A larger non-uniformity in the vertical direction was found compared to that in the horizontal direction. These results suggest the possibility of non-uniform environmental conditioning. A rough estimation of the energy consumption by the two different condition modes, namely zone-specific and overall conditioning, was made. A huge energy saving of 69.6 % by the zone-specific conditioning mode was revealed compared to the overall conditioning. This implies a huge advantage in energy efficiency by non-unform environmental conditioning technologies applied in greenhouses. The study provides useful data for understanding non-uniform environments in greenhouses and the application of non-uniform environmental conditioning technologies.

Influence of microclimate control on the growth of asparagus under greenhouse in tropical climates

High temperatures have become common in cities in Taiwan, and this phenomenon has spread to surrounding agricultural areas. Tainan, a city located in a tropical climate zone with agriculture as its primary development industry, is one of the cities considerably affected by the high temperature. High temperatures can reduce crop yields and even cause plant death, especially for vulnerable high-value crops, which are severely to microclimate conditions. Asparagus is a high-value crop that has long been cultivated in the Jiangjun District of Tainan. Recently, asparagus has been planted in greenhouses to protect against pests and natural disasters. However, the greenhouses can overheat. To identify the optimal growth environment for asparagus, this study applies vertical monitoring to record the temperature in the greenhouse and the soil moisture content of a control (canal irrigation) and an experimental (drip irrigation) group. When the surface layer of the soil exceeds 33°C, the tender stems of asparagus bloom readily, reducing its commercial value. Therefore, drip irrigation was conducted with cool water (26°C) to reduce soil temperature in summer and warm water (28°C) to increase soil temperature in winter. The study also recorded the growth of asparagus using daily yields measured by farmers during weighing and packing to understand the benefits of controlling the greenhouse microclimate. This study reports a correlation of 0.85 between asparagus yield and temperature and a correlation of 0.86 between asparagus yield and soil moisture content. The use of a drip irrigation system with a water temperature adjustment function not only saves up to 50% of water but also resulted in an average yield increase of 10% through maintaining stable soil moisture content and temperature. Therefore, the findings of this study can be applied to asparagus yields affected by high temperature and can solve the problems of poor quality in summer and low yield in winter.

A Food Waste-Derived Organic Liquid Fertiliser for Sustainable Hydroponic Cultivation of Lettuce, Cucumber and Cherry Tomato

We previously reported a sustainable food waste management approach to produce an acceptable organic liquid fertiliser for recycling food waste called "FoodLift." This study follows our previous work to evaluate the macronutrients and cation concentrations in harvested structural parts of lettuce, cucumber, and cherry tomatoes produced using food waste-derived liquid fertiliser (FoodLift) and compare them against commercial liquid fertiliser (CLF) under hydroponic conditions. N and P concentrations in the structural parts of lettuce and the fruit and plant structural parts of cucumber appear to be similar between FoodLift and CLF (p > 0.05), with significantly different N concentrations in the various parts of cherry tomato plants (p < 0.05). For lettuce, N and P content varied from 50 to 260 g/kg and 11 to 88 g/kg, respectively. For cucumber and cherry tomato plants, N and P concentrations ranged from 1 to 36 g/kg and 4 to 33 g/kg, respectively. FoodLift was not effective as a nutrient source for growing cherry tomatoes. Moreover, the cation (K, Ca, and Mg) concentrations appear to significantly differ between FoodLift and CLF grown plants (p < 0.05). For example, for cucumber, Ca content varied from 2 to 18 g/kg for FoodLift grown plants while Ca in CLF-grown cucumber plants ranged from 2 to 28 g/kg. Overall, as suggested in our previous work, FoodLift has the potential to replace CLF in hydroponic systems for lettuce and cucumber. This will lead to sustainable food production, recycling of food waste to produce liquid fertiliser, and will promote a circular economy in nutrient management.

Hydroponic Cultivation of Vine Leaves with Reduced Carbon Footprint in a Mediterranean Greenhouse

Vine leaves are considered a delicacy food however they are only produced as a byproduct for a short harvest period due to grape cultivation practices and numerous chemical applications. In this work, vine plants were cultivated hydroponically in a greenhouse, to extend the cultivation period and along with high plant density, maximize fresh leaves yield. Four different substrates were tested—Perlite, Perlite-Attapulgite, Perlite-Zeolite, 1.7Perlite-higher density planting—with soil treatment as a control, and the experimental cultivation lasted a total of about seven months in the year 2021. Quantitative and qualitative characteristics such as leaves number and weight, color of leaves, nitrates, photosynthetic parameters, total phenols, and plant nutrient concentrations were assessed, while the product’s environmental impact was calculated. The 1.7Perlite treatment produced a 1.6–2.0 times higher number of leaves per hectare than the other hydroponic treatments and 8.7 times higher than the soil treatment, while no statistically significant differences were found regarding qualitative characteristics. Consequently, the 1.7P treatment resulted in a 1.4 to 7.6 times lower product carbon footprint compared to the other treatments. In future research, substrates water and nutrient retention will be further studied along with year-round production in a heated greenhouse with full climate control so that plants are kept evergreen.

Research on the Microclimate of Protected Agriculture Structures Using Numerical Simulation Tools: A Technical and Bibliometric Analysis as a Contribution to the Sustainability of Under-Cover Cropping in Tropical and Subtropical Countries

The use of protected agriculture structures in tropical and subtropical countries is the main alternative for intensification of agricultural production selected by producers. In general, in these regions, passive and plastic-covered structures predominate, with natural ventilation as the only method of climate control. This phenomenon has been widely studied in different types of structures using computational fluid dynamics (CFD) simulation. Therefore, this review aimed to collect and analyze the publications generated in this field of knowledge between 2010 and 2020. The search for information included the main academic databases available on the web and the analysis was carried out using bibliometric techniques, from which it was possible to identify details inherent to the scientific production, such as countries of origin, main authors, journals, and citations. Likewise, a detailed breakdown of the relevant technical information of the three phases of numerical simulation, such as preprocessing, processing, and postprocessing, was carried out. A compilation of 118 papers published in 65 journals, written by 256 authors, originating from 24 countries was achieved, where it was evident that Mexico and Colombia were the countries with the highest scientific production in the last decade. These papers analyzed, together, a total of 17 different types of structures where polyethylene-covered greenhouses predominated, with steady state simulations, for daytime climate conditions and without the presence of crops. Within the current and future research trends, the predominance of studies analyzing passive climate control methods, new models of insect-proof mesh-house structures, and, finally, studies focused on the structural analysis of greenhouses was found.

Recycling of food waste to produce chicken feed and liquid fertiliser

Most of the food waste (FW) generated by commercial activities and the majority of household FW is collected as part of general waste, which is either incinerated or landfilled. There is an increasing interest in the collection of FW as a separate waste stream and use it for the production of compost or recovery of energy through anaerobic digestion (AD) or pyrolysis. This study focused on using FW to produce chicken feed and liquid fertiliser (CFLF). The food waste samples were collected from food related businesses such as service club, café, restaurant, bakery and supermarket. The CFLF process was used to produce chicken feed pellets containing 19% of protein content, which is within the range of 16 to 22% of most commercial chicken feed pellets and within the National Research Council (NRC) recommended range of 15 to 23%. The liquid extract derived from CFLF process had high nutrient concentrations similar to those present in the feed solution used in hydroponic systems. Hence, the liquid extract from CFLF can be used to replace the commercial liquid fertiliser used in hydroponic systems. Environmental impact analysis of CFLF process using GaBi life cycle analysis (LCA) software indicated that the CFLF process can yield environmental credits for 15 out of 19 categories of impacts considered in the analysis. The measured environmental credits were significantly higher than the other disposal options such as, anaerobic digestion (AD), incineration and landfill.

Smart glass impacts stomatal sensitivity of greenhouse Capsicum through altered light

Optical films that alter light transmittance may reduce energy consumption in high-tech greenhouses, but their impact on crop physiology remains unclear. We compared the stomatal responses of Capsicum plants grown hydroponically under control glass (70% diffuse light) or the smart glass (SG) film ULR-80, which blocked >50% of short-wave radiation and ~9% of photosynthetically active radiation (PAR). SG had no significant effects on steady-state (gs) or maximal (gmax) stomatal conductance. In contrast, SG reduced stomatal pore size and sensitivity to exogenous abscisic acid (ABA), thereby increasing rates of leaf water loss, guard cell K+ and Cl- efflux, and Ca2+ influx. SG induced faster stomatal closing and opening rates on transition between low (100 µmol m-2 s-1) and high PAR (1500 µmol m-2 s-1), which compromised water use efficiency relative to control plants. The fraction of blue light (0% or 10%) did not affect gs in either treatment. Increased expression of stomatal closure and photoreceptor genes in epidermal peels of SG plants is consistent with fast stomatal responses to light changes. In conclusion, stomatal responses of Capsicum to SG were more affected by changes in light intensity than spectral quality, and re-engineering of the SG should maximize PAR transmission, and hence CO2 assimilation.

Analysis of Inlet Configurations on the Microclimate Conditions of a Novel Standalone Agricultural Greenhouse for Egypt Using Computational Fluid Dynamics

Water shortage, human population increase, and lack of food resources have directed societies towards sustainable energy and water resources, especially for agriculture. While open agriculture requires a massive amount of water and energy, the requirements of horticultural systems can be controlled to provide standard conditions for the plants to grow, with significant decrease in water consumption. A greenhouse is a transparent indoor environment used for horticulture, as it allows for reasonable control of the microclimate conditions (e.g., temperature, air velocity, rate of ventilation, and humidity). While such systems create a controlled environment for the plants, the greenhouses need ventilation to provide fresh air. In order to have a sustainable venting mechanism, a novel solution has been proposed in this study providing a naturally ventilating system required for the plants, while at the same time reducing the energy requirements for cooling or other forced ventilation techniques. Computational fluid dynamics (CFD) was used to analyse the ventilation requirements for different vent opening scenarios, showing the importance of inlet locations for the proposed sustainable greenhouse system.

A Supervisory Control Strategy for Improving Energy Efficiency of Artificial Lighting Systems in Greenhouses

Artificial lighting systems are used in commercial greenhouses to ensure year-round yields. Current Light Emitting Diode (LED) technologies improved the system efficiency. Nevertheless, having artificial lighting systems extended for hectares with power densities over 50W/m2 causes energy and power demand of greenhouses to be really significant. The present paper introduces an innovative supervisory and predictive control strategy to optimize the energy performance of the artificial lights of greenhouses. The controller has been implemented in a multi-span plastic greenhouse located in North Italy. The proposed control strategy has been tested on a greenhouse of 1 hectare with a lighting system with a nominal power density of 50 Wm−2 requiring an overall power supply of 1 MW for a period of 80 days. The results have been compared with the data coming from another greenhouse of 1 hectare in the same conditions implementing a state-of-the-art strategy for artificial lighting control. Results outlines that potential 19.4% cost savings are achievable. Moreover, the algorithm can be used to transform the greenhouse in a viable source of energy flexibility for grid reliability.

Thermo-Environmental Assessment of a Heated Venlo-Type Greenhouse in the Yangtze River Delta Region

Accurate evaluation of microclimate conditions in a greenhouse can assist producers to manage crop production and designers to optimize climate control systems. An assessment of the variable thermo-environmental behavior of a heated Venlo-type greenhouse under the influence of naturally changing climate conditions in the Yangtze River Delta region was undertaken. A three-dimensional transient computational fluid dynamics (CFD) model was developed to analyze the airflow pattern and dynamic distribution of temperature and humidity inside the greenhouse. Validation of the numerical model showed a satisfactory agreement between measured and simulated values of air velocity, temperature, and absolute humidity, with mean hourly air temperature mean absolute error (MAE) and root mean square error (RMSE) values of 7.7% and 7.9%, respectively, and mean hourly air humidity MAE and RMSE values of 16.18% and 16.42%, respectively. Simulation results demonstrated that the airflow pattern shaped the distribution of temperature and absolute humidity, and homogeneity of both variables was prevalent inside the greenhouse. These results could be adopted by growers and designers in the Yangtze River Delta region and other sub-tropical climatic regions to improve crop production and optimize climate control systems.

3D Numerical Analysis of the Natural Ventilation Behavior in a Colombian Greenhouse Established in Warm Climate Conditions

Global food production and availability in hot climate zones are limited by biotic and abiotic factors that affect agricultural production. One of the alternatives for intensifying agriculture and improving food security in these regions is the use of naturally ventilated greenhouses, an alternative that still requires information that allows technical criteria to be established for decision-making. Therefore, the objective of this work was to study the spatial distribution of temperature and relative humidity inside a greenhouse built in the Colombian Caribbean. The methodological approach included the implementation of an experimentally validated 3D numerical simulation model. The main results obtained allowed to determine that the airflows generated inside the greenhouse had average velocities below 0.5 m/s and were mainly driven by the thermal effect of natural ventilation. It was also found that the gradients generated between the interior of the structure and the exterior environment presented values lower than 2.0 °C for temperature and −6.3% for relative humidity. These values can be considered low in comparison with other structures evaluated in other regions of the world where the gradients can reach values higher than 10 °C and 13% for temperature and relative humidity, respectively.

Sustainable Protected Cropping: A Case Study of Seasonal Impacts on Greenhouse Energy Consumption during Capsicum Production

Sustainable food production in protected cropping is increasing rapidly in response to global climate change and population growth. However, there are significant knowledge gaps regarding energy consumption while achieving optimum environmental conditions for greenhouse crop production. A capsicum crop cultivated in a high-tech greenhouse facility in Australia was analysed in terms of relationships between key environmental variables and the comparative analysis of energy consumption during different seasons. We showed that daily energy consumption varied due to the seasonal nature of the external environment and maintenance of optimal growing temperatures. Total power consumption reported throughout the entire crop cycle for heating (gas hot water system) and cooling (pad and fan) was 12,503 and 5183 kWh, respectively; hence, heating consumed ca. 70% of the total energy requirement over the 8-month growing period (early spring to late autumn) in the greenhouse facility. Regressions of daily energy consumption within each season, designated either predominantly for heating or cooling, indicated that energy consumption was 14.62 kWh per 1 °C heating and 2.23 kWh per 1 °C cooling. Therefore, changing the planting date to late spring is likely to significantly reduce heating energy costs for greenhouse capsicum growers in Australia. The findings will provide useful guidelines to maximise the greenhouse production of capsicum with better economic return by taking into consideration the potential optimal energy saving strategy during different external environment conditions and seasons.

Innovations in plant genetics adapting agriculture to climate change

Developing new genotypes of plants is one of the key options for adaptation of agriculture to climate change. Plants may be required to provide resilience in changed climates or support the migration of agriculture to new regions. Very different genotypes may be required to perform in the modified environments of protected agriculture. Consumers will continue to demand taste, convenience, healthy and safe food and sustainably and ethically produced food, despite the greater challenges of climate in the future. Improving the nutritional value of foods in response to climate change is a significant challenge. Genomic sequences of relevant germplasm and an understanding of the functional role of alleles controlling key traits will be an enabling platform for this innovation.