Deep-water Culture System Research Articles

Greenhouse production of baby leaf vegetables using rainbow trout wastewater in a high-tech vertical decoupled aquaponic system

IntroductionAquaponics is an integrated food production system that links recirculating aquaculture with hydroponics, leading to higher water use efficiency than conventional food production systems while also saving on fertilizers. In the present study, baby lettuce and baby rocket plants cultivated hydroponically in a deep water culture system using wastewater from rainbow trout were evaluated as part of a vertical decoupled aquaponic system.Materials and methodsMore specifically, three different nutrient solutions were supplied: a) using fish wastewater only (designated as Fish); b) fish wastewater enriched with synthetic fertilizers (Mix); and c) a typical nutrient solution (Hoagland) as the control. Both lettuce and rocket plants were monitored in these nutrient solutions and in two different substrates, peat and perlite, as an organic and an inert substrate, respectively. The purpose of this study was to assess a vertical decoupled aquaponic system with regard to the resource use efficiency, such as water, land, and energy, while evaluating plant cultivation in the different treatments in terms of yield, growth, nitrate concentration on the leaf tissue, and foliar analysis. The photosynthetic rate and leaf color indices were also considered in the plant evaluation.ResultsThe Mix–Peat treatment was the most efficient growing combination in terms of land and water use efficiency, with approximately 7% better land use efficiency while using 38% less water and 10% less fertilizer than Hoagland–Peat. Moreover, lettuce plants had the highest yield in the Mix–Peat treatment, at 2,497 g m−2, which was approximately 6% higher than that of Hoagland–Peat while not being inferior in the quality measures. On the other hand, the yield of rocket was significantly higher in the Hoagland–Peat treatment, being 18% higher than that of Mix–Peat and 30% higher than that of Fish–Peat. Overall, the study confirmed that aquaponic systems could lead to higher water use efficiency and savings in fertilizers without undermining the yield and quality of lettuce, while the vertical arrangement developed within the scope of this study can increase the land useefficiency of the system.

Количествен анализ на хранителните разтвори на три аквапонични системи

The effects of nutrient flows on tilapia fish (Oreochromis niloticus) and plant crops in three model aquaponic systems (deep water culture system, nutrient film technique and substrate beds) placed under identical conditions were evaluated. Quantitative analysis of ammonia, nitrite, nitrate concentrations and the factors on which they depend (air and fish water temperature, air humidity, pH and dissolved oxygen) was performed. The nutrient solutions affecting the yield and quality of the produce and the efficiency of the resources used were assessed. Monitoring and good management of aquaponics are necessary and mandatory requirements to ensure optimal conditions for the symbiosis between fish, beneficial bacteria and plants.

Valorization of wastewater from industrial hydroponic cultivations using the microalgal species Chlorella vulgaris

The continuous increase in the world population is associated with a greater demand for food. This need has driven the development of new cultivation systems capable of producing large quantities of vegetable biomass in a small space, with precise and regulated control of the use of resources. Among these, vertical farms are systems developed in height, and they produce continuously throughout the year.The hydroponic system is commonly used in vertical farming and entails the growth of plants in a solution rich in nutrients, easily assimilated by plants. However, hydroponic solutions still contain nutrient salts at the end of the productive cycle. Consequently, spent hydroponic solutions cannot be directly released into the environment because they would cause water pollution. Thus, they need to be appropriately treated, increasing production costs.Microalgae represent a cost-effective solution for treating and valorizing hydroponic wastewater. They can easily consume the residual nutrients, generating valuable biomass that can be exploited as a biofertilizer, a biostimulant, or even as a valuable food supplement.The present work showed the ability of the model eukaryotic microalga Chlorella vulgaris to use valuable resources derived from industrial cultivations of basil and tobacco in a hydroponic deep-water culture system. Although the use of spent hydroponic solutions slightly affected the microalgal biomass accumulation of more than ~40 % compared to the fresh solution, possibly due to the presence of root exudates that have an antagonistic effect toward microalgae, the phytoremediation activity of microalgae was achieved. The reported results described the consumption of more than 80 % and 70 % of P and N residual nutrients in hydroponic formulations, respectively. Moreover, more than 2 g/L of microalgal biomass was generated after 7 days of growth in air-lifted photobioreactors. The outcomes of this research provide new insights toward greater sustainability of vertical farming, following circular economy principles.

Multi-season Evaluation of Substrates for Optimized Arugula and Lettuce Production in Hydroponics

Rockwool and peatmoss are commonly used substrates in the greenhouse industry due to their quality, stable pH, exceptional water retention properties and air porosity that is important for plant root development. Although rockwool is commonly used in deep water culture (DWC) hydroponic systems as the base support, there is a lack of studies comparing different types of substrates that could be used in DWC systems, especially considering the increasing market value and awareness of sustainable production in controlled environment agriculture. We identified 13 commercial substrate mixes with different compositions and conducted a series of studies in a DWC system in a greenhouse for three seasons to evaluate their effects on arugula ‘Slow Bolt’ (Eruca sativa L.) and lettuce ‘Summer Crisp’ (Lactuca sativa L.) growth, yield, and quality. The substrates tested significantly influenced the growth, yield, and quality of both arugula and lettuce. The average leaf fresh weight per plant could range from 44 to 190 g for arugula and 89 to 265 g for lettuce. The peat-based products outperformed the coir and other inorganic substrates (phenolic foam, rockwool). The substrate with 75% peat + 25% fine coir produced the greatest plant height, width, and biomass for arugula and lettuce over three growing seasons. Examining arugula and lettuce growth, the fall season produced plants with higher water and nutrient use efficiency, while plants grown during the winter had lower resource use efficiency. Further research is needed to engineer hydroponic substrates suitable for various seasons of leafy green production that results in comparable yield and quality.

An Innovative Co-Cultivation of Microalgae and Actinomycete-Inoculated Lettuce in a Hydroponic Deep-Water Culture System for the Sustainable Development of a Food–Agriculture–Energy Nexus

In recent years, researchers have turned their attention to the co-cultivation of microalgae and plants as a means to enhance the growth of hydroponically cultivated plants while concurrently producing microalgal biomass. However, the techniques used require precise calibration based on plant growth responses and their interactions with the environment and cultivation conditions. This study initially focused on examining the impact of hydroponic nutrient concentrations on the growth of the microalga Chlorella sp. AARL G049. The findings revealed that hydroponic nutrient solutions with electrical conductivities (EC) of 450 µS/cm and 900 µS/cm elicited a positive response in microalgae growth, resulting in high-quality biomass characterized by an elevated lipid content and favorable properties for renewable biodiesel. The biomass also exhibited high levels of polyunsaturated fatty acids (PUFAs), indicating excellent nutritional indices. The microalgae culture and microalgae-free culture, along with inoculation-free lettuce (Lactuca sativa L. var. longifolia) and lettuce that was inoculated with plant growth actinobacteria, specifically the actinomycete Streptomyces thermocarboxydus S3, were subsequently integrated into a hydroponic deep-water culture system. The results indicated that several growth parameters of lettuce cultivated in treatments incorporating microalgae experienced a reduction of approximately 50% compared to treatments without microalgae, and lowering EC levels in the nutrient solution from 900 µS/cm to 450 µS/cm resulted in a similar approximately 50% reduction in lettuce growth. Nevertheless, the adverse impacts of microalgae and nutrient stress were alleviated through the inoculation with actinomycetes. Even though the co-cultivation system leads to reduced lettuce growth, the system enables the production of high-value microalgal biomass with exceptional biodiesel fuel properties, including superior oxidative stability (>13 h), a commendable cetane number (>62), and a high heating value (>40 MJ/kg). This biomass, with its potential as a renewable biodiesel feedstock, has the capacity to augment the overall profitability of the process. Hence, the co-cultivation of microalgae and actinomycete-inoculated lettuce appears to be a viable approach not only for hydroponic lettuce cultivation but also for the generation of microalgal biomass with potential applications in renewable energy.

Value-added green biorefinery co-products from ultrasonically assisted DES-pretreated Chlorella biomass

This study pursued the goal of creating value-added co-products through an environmentally friendly biorefinery approach, employing ultrasonically assisted deep eutectic solvent (DES)-pretreated Chlorella biomass. The primary focus was on generating enriched biodiesel feedstock with exceptional fuel properties and developing hydroponic biofertilizer. The results demonstrated the effectiveness of a two-step process involving a 5-minute ultrasound-assisted DES pretreatment followed by ultrasound-assisted solvent extraction, which efficiently extracted lipids from Chlorella biomass, yielding biodiesel-quality lipids with good cetane number (59.42) and high heating value (40.11 MJ/kg). Notably, this two-step approach (78.04 mg-lipid/g-microalgal biomass) led to a significant 2.10-fold increase in lipid extraction compared to a one-step process (37.15 mg-lipid/g-microalgal biomass) that combined ultrasound-assisted DES pretreatment and solvent extraction. Importantly, the aqueous extract derived from lipid-extracted microalgal biomass residues (LMBRs) showed promise as a component in hydroponic biofertilizer production, supporting lettuce growth in hydroponic deep water culture system. Consequently, microalgae biorefinery co-products hold tremendous potential in enhancing the profitability and sustainability of interconnected sectors, encompassing renewable energy, agriculture, and the environment.

Effects of Nitrogen Concentration on Growth, Yield and Phytochemical Content of Persicaria minor Cultivated Using Hydroponics System

Persicaria minor or locally known as kesum from the family Polygonaceae is a common herbal plant found in Malaysia. Hydroponic cultivation of kesum using deep water culture (DWC) system can be an alternative option for kesum growers in increasing crop yields. The deep water culture system is a method in which liquid fertiliser solution is given directly to the plant roots without any medium and water flow. The study’s main objective was to determine the effects of nitrogen concentration on growth, yield and phytochemical content of kesum cultivated using hydroponic system. Plants were grown under one of four nitrogen concentration solution regimes and the experiment was conducted under a side netted rain shelter. The four treatments comprised of 200 mg/L, 100 mg/L, 50 mg/L and 0 mg/L of nitrogen concentrations. The experiment was arranged in Randomized Complete Block Design (RCBD) with 4 replications. Plants were selected randomly and harvested eight weeks after planting. Plants grown supplemented with 100 mg/L of nitrogen concentration gave the best growth performance and biomass yield. They produced the highest plant height (78 cm) and fresh biomass yield (174 g per plant). Meanwhile plants supplemented with 50 mg/L of nitrogen concentration produced the highest Quercetin-3-glucuronide (Q3G) (98.261 mg/mL) and Quercitrin (61.367 mg/mL) compound compared to the other treatments. However, plants treated with 0 mg/L of nitrogen concentrations exhibited major nutrients deficiencies symptoms and die after 3 weeks of planting. Hence, it can be concluded that the kesum plants cultivated using hydroponics’ deep water culture system supplemented with 100 mg/L of nitrogen concentration gave the highest plant growth and biomass yields. However, to obtain higher Quercetin-3-glucuronide and Quercitrin compound, 50 mg/L of nitrogen concentration is recommended.

Agronomic Performance and Phytochemical Profile of Lettuce Grown in Anaerobic Dairy Digestate

Anaerobic liquid dairy digestate is a by-product of dairy waste anaerobic digestion from dairy operations and is associated with environmental risks if not handled properly, particularly nutrient leaching losses, water contaminations, and greenhouse gas emissions. We tested the applications of anerobic digestate (AD) as a biofertilizer and water source in greenhouse vegetable production to integrate food production and industry waste management for sustainable environments. We used a deep water culture system to assess the effects of AD effluent alone, inorganic nutrient solution (NS), and a combination of AD and NS on the growth, yield, and phytonutrient profile and heavy metal contamination assessment of hydroponically produced lettuce. Lettuce produced in AD had a lower leaf area, total chlorophyll content, and fresh biomass; however, it displayed significantly higher chicoric acid (200%), chlorogenic acid (67%), luteolin (800%), quercetin-3-O-β-d-glucuronide (378%), quercetin-3-glucoside (200%), quercetin-3-O-(6″-O-malonyl)-β-D-glucoside (1077%), folate (248%), pantothenic acid (200%), total phenolics (111%), total antioxidants (44%), and soluble sugars (253%) compared to control (inorganic feed). The AD-produced lettuce also showed significantly lower heavy metal bioaccumulation risks associated with the human consumption. Based on various results, we may conclude that AD utilization in hydroponics can offer a sustainable solution to harvest a better lettuce yield, higher phytonutrients, and environmental benefits.

Comparison of Energy-use Efficiency for Lettuce Plantation under Nutrient Film Technique and Deep-Water Culture Hydroponic Systems

Energy conservation opportunities in closed plant production systems have been widely discussed, however, a comparison of energy-use efficiency (EUE) for different types of hydroponic systems is lacking. This paper compares the EUE of two different hydroponic systems, namely nutrient film technique (NFT) and deep-water culture (DWC), within an aquaponics facility. The energy is monitored in a controlled environment using artificial lighting and its impact on the growth dynamics of the crops is measured, in this case, on a leafy green crop (Lactuca Sativa L. ‘Little Gem’). Offering better efficiency and reliability, light-emitting diode (LED) irradiation is used with a photosynthetic photon flux (PPF) of 140 µmol·s−1 and a photoperiod of 12-hours. The seeds are then placed in growth chambers, kept at an ambient temperature of 18°C for 21 days. These seedlings are then transplanted in rockwool cubes, followed by placement in NFT or DWC systems in equal numbers. Both systems are illuminated with LED irradiation having a PPF of 200 µmol·s−1. Continuous irradiation with a photoperiod of 16-hours is provided to both systems for 5 weeks. Crop growth parameters, such as leaf count and plant height, are measured in both systems resulting in similar numbers obtained, however, shoot fresh weight, leaf area, and root length are significantly different. Furthermore, the NFT system exhibited an EUE of 31.3 g. kWh−1 and outperformed the DWC system with an EUE of 24.53 g. kWh−1; indicating higher growth and better energy savings associated with NFT systems. These results suggest that NFT systems has a higher potential to offer better energy-use efficiency for producing crops in plant factories and aquaponics facilities.

Symbiotic association of microalgae and plants in a deep water culture system.

In this study, microalgae culture (Chlorella vulgaris) and mint seedlings (Mentha spp.) were combined in a hydroponic system to improve plant growth. Mint seedlings were grown both in microalgae-containing and in microalgae-free trial groups, and both groups were subjected to aerated and non-aerated conditions to show the effect of aeration and microalgae co-cultivation on the mint weight and height. The plant quality was also determined with color measurements of the mint leaves. The increase in the weight of the plants was the highest in microalgae-containing and aerated group (0.47 g) and the lowest in microalgae-free and non-aerated group (0.22 g). On the other hand, the variation in the plant height was not significant between the groups, the growth was lateral. The best quality mint leaves were also produced in microalgae-containing and aerated group. Our results have revealed the symbiotic life of the mint plant placed in the hydroponic system with microalgae and demonstrated improved mint growth and quality. This co-cultivation system is also potentially more environmentally friendly compared to growing microalgae and mint independently because of lower cost of aeration and mixing for microalgae cultivation, higher nutrient consumption efficiency, and reduced nutrient outflow.

A Study of the Effectiveness of Hydroponic Growing Variables on Lactuca sativa var. capitata

Hydroponic growing in controlled environment horticulture has been an increasingly used method of produce production around the world. Its many methods integrate sustainability and growth efficiency through the control of climatic and system variables. This study investigated control variables that would produce and market a more effective lettuce (lactuca sativa. var capitata) crop. Three objectives determined: The comparison between the dimensions of deep water culture systems and the lettuce harvesting length, Consumer and ICP spectrometry recognition of different post-harvest hydroponic nutrient concentration, and the preference of lettuce grown in different hydroponic nutrient concentrations. Through growing trials and consumer tests, it was found that the 14 gallon (102 x 50.8 x 66cm) size deep water culture system also produced lettuce with larger harvest-length; spectrometry recognition of lettuce crops grown in different nutrient levels was effective with 7 of the 12 nutrients elements showing sufficient results of concentration in concentrated lettuce. Consumer identification recognition wasn’t successful with 40% of consumers unable to recognize any nutrient concentration level compared to two other varieties. Representing a diverse market audience, of consumers determined that variety 127 (50% regular concentration) was preferred as significant market influence of purchase. This research will impact future studies in effective small scale hydroponic growing and growers looking to expand knowledge of beneficial growth.

High Nutrient Concentrations of Hydroponic Solution Can Improve Growth and Nutrient Uptake of Spinach (Spinacia oleracea L.) Grown in Acidic Nutrient Solution

Hydroponic leafy green production offers high productivity and quality of crops but requires good management of pH and electrical conductivity (EC) to optimize the nutrient uptake. Nutrient solution pH is typically managed between 5.5 and 6.5, whereas lowering pH to more acidic range (e.g., <5.0) can potentially mitigate problematic waterborne diseases. Plant response to low pH is species specific and generally involves direct effect of increased hydronium ions and indirect effects of pH-dependent factors, such as low cations availability. To develop a new hydroponic nutrient management strategy, ‘Corvair’ spinach plants were grown under pH 4.0, 4.5, 5.0, and 5.5 of a hydroponic nutrient solution using a deep-water culture system in a growth chamber. Spinach shoot and root mass after 19 to 20 days declined with lowering pH. At the lowest pH of 4.0, plants displayed stunted overall growth and severely inhibited root development. Plant growth and morphology at pH 4.5 or 5.0 were normal but small, suggesting that growth reduction at these pH was likely a result of reduced nutrient uptake. Plant tissue analyses showed decreased N, P, K, Mg, S, Cu, Fe, Mn, and Zn concentration as pH decreased. When the strength of nutrient solution was increased three times at a low pH 4.5 to improve the overall nutrient availability, spinach shoot and root fresh weight with high nutrient concentrations (EC 3.4 dS·m−1) significantly improved but was still lower than those in the control (pH 5.5 and EC 1.4 dS·m−1), respectively. Plant tissue analysis showed that lowering pH to 4.5 significantly reduced tissue concentrations of P, K, Ca, Mg, S, Cu, Mn, and Zn compared with those in the control. Under low pH and increased EC treatment (pH 4.5 and EC 3.4 dS·m−1), all dry leaf nutrient concentrations were similar or higher than those of the control, except Mg and Zn, which showed a lower concentration than the control with a weak significance (P < 0.06). This suggests that additional optimization of nutrient formula might further improve the spinach growth at low pH. Together, our results will help to develop a new and low-cost nutrient management methodology to produce leafy greens hydroponically.

Exploring Unconventional Growing Methods to Promote Healthy Growth in Common Household Plants: Tagetes patula L. and Lepidium sativum

Chemical fertilizers have been used in increasing quantities for household gardening and commercial agriculture worldwide since their advent during the Green Revolution. Such fertilizers have detrimental impacts on the environment, contributing to nutrient runoff and aquatic dead zones. At the same time, water consumption for agricultural needs has
 skyrocketed. Alternative growing methods are urgently needed to reduce the impacts of plant cultivation. This study focused on finding more sustainable growing methods that reduce chemical fertilizer or water usage and can be used at the household level for garden plants. We hypothesized that the alternative growing methods would better encourage healthy plant growth as compared to a control. Several marigold (Tagetes patula L.) and garden cress (Lepidium sativum) plants were observed over a 13-week period. Metrics for healthy plant growth were height at first bloom, growing time, and survival rate. The results indicated that the treatments did not have a statistically significant effect on marigold and garden cress growth times in addition to marigold heights. However, the Deep Water Culture (DWC) treatment for garden cress plants significantly increased the height at first bloom compared to the control group. For rates of surviving plants, the treatments had little effect on garden cress, but the Eggshell Grounds, Wick System, and DWC system groups outperformed the control group for marigolds.

Application of Biological Nitrogen Fixation Cyanobacteria To Paddy Plant Cultivated Under Deep-Water Culture System

The Biological Nitrogen Fixing (BNF) cyanobacteria can reduce atmospheric nitrogen into ammonium. This ability makes BNF cyanobacteria a potential eco-friendly N-source for soil-planted pad-dy. Apart from a few success stories of BNF cyanobacteria applica-tion in the rice field, its role as an ammonium producer is still an open question. There is also a possibility that indeed cyanobacteria biomass which provides nitrogen through the biological decomposing process. This study aimed to analyze the influence of three strains BNF cyanobacteria on paddy grown in the Deep-Water Culture (DWC) hydroponic system. Yoshida Nutrient Solution was used as a growth medium with the application of 0, 45.7, and 91.4 gL-1 of ammonium nitrate (NH4NO3) with five replications. The result showed that inter-action between cyanobacteria and nitrogen significantly influenced the total nitrogen of paddy plant, but not the paddy plant height, the num-ber of tillers, and biomass. Cyanobacterial filaments were found most-ly attached to the paddy root rather than floated in the DWC system. Paddy treated with cyanobacteria had more lateral root than control. The result suggested that cyanobacteria support paddy growth indi-rectly through nitrogen deposition in plant tissue and root development.

Evaluation of hydroponic systems for the cultivation of Lettuce (Lactuca sativa L., var. Longifolia) and comparison with protected soil-based cultivation

The expansion of the earth's population has led to the overuse of land and water resources, which has ultimately resulted in their scarcity. Changing climatic conditions and erratic weather behavior over the years has fueled the existing problems of land and water scarcity and continued to exact a toll on agriculture. Utilization of the latest technologies coupled with advanced methods of crop production will no doubt increase our capacity to deal with these modern challenges of the shortages of resources. Soilless or liquid culture may serve as an alternative to conventional soil-based cultivation systems. The present study was conducted to determine the suitability and viability of hydroponic cultivation as an alternative planting system to greenhouse soil-based lettuce cultivation in temperate regions of northern India. In the present study, two hydroponic techniques viz. deep water culture, and nutrient film technique were evaluated and compared to the conventional soil-based cultivation method under protected conditions. Crop performance, water consumption, and economy were the criteria chosen to assess the efficacy of planting techniques using Tukey’s multiple range test at a significance level of 0.05. Deep water culture system was found to be the most desirable concerning the duration of the crop, causing a reduction in the plant growth period by 15 days. Also, higher values of most of the photosynthetic parameters were observed in the deep water culture system, which translated into higher yield/plant for the system. The crop quality also improved under the deep water culture system, which was reflected by the higher values of quality parameters like chlorophyll, total soluble solids, protein, and crude fiber content. Both the hydroponic systems produced significantly higher yield, and nutritionally superior produce in lesser time than the soil-based system (P < 0.05). However, there was a significant reduction in the dry matter content under hydroponic conditions. Nutrient film technique resulted in significant water savings of 64% than the other two techniques. According to economic analysis indicators, both hydroponic techniques performed better than the soil-based systems, having benefit-cost ratios greater than 2. Out of the two techniques tested, deep water culture proved to be the most promising system for adoption under protected agriculture owing to its simplicity, ease of operation, higher yield, economic feasibility, and nutritionally superior produce. The results of the study established hydroponic lettuce production as an appropriate and sustainable alternative to conventional soil-based lettuce production.

Comparing hydroponic and aquaponic rootzones on the growth of two drug-type Cannabis sativa L. cultivars during the flowering stage

The cultivation of drug-type Cannabis sativa Lin. (C. sativa) employs a variety of rootzone systems, yet little is understood about rootzone-effects on plant physiology, inflorescence biomass, and cannabinoid potency. To determine if rootzone systems can affect C. sativa growth, physiology, and inflorescence biomass and phytochemicals, two C. sativa cultivars, colloquially known as ‘Nordle’ and ‘Sensi-Star’, were grown in three rootzone systems in a controlled environment. The three tested rootzone systems were: 1) an 11-litre pot containing a peat-based growing substrate, top fertigated with a synthetic fertilizer solution (“hydroponic”); 2) an 11-litre pot containing a peat-based growing substrate, top fertigated with aquaculture effluent solution (“aquaculture”); and 3) a 3-litre pot containing a custom made, predominantly peat-based growing substrate, with the lower portion of the roots submerged in a conventional aquaponics deep-water culture system (“aquaponics”). Throughout the experiment, plant growth (height, branch number, canopy volume), leaf-level physiological traits (e.g., chlorophyll) foliar mineral nutrition, and substrate physio-chemical properties were measured. At experimental completion, inflorescence yield (dry biomass) and potency (mass-based cannabinoid and terpene concentrations) were determined. Results revealed, significant rootzone-effects on most growth and physiological traits measured. Plants performed best in the in the hydroponic rootzone: e.g., producing 42–116% greater inflorescence biomass than the other rootzone systems. In contrast, however, Nordle plants in the aquaponics treatment had greater Δ9-tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA), and the terpenes ß-pinene and limonene, relative to their congeners grown in the other rootzones investigated. Pronounced differences in substrate macro-nutrient availability and foliar nutrient content occurred among the rootzones, suggesting a potential mechanism to explain the observed growth, physiological, yield and potency responses. This work underscores the importance of the rootzone environment for the cultivation of C. sativa, specifically in indoor systems focused of medical or research production.

Effects of Low pH of Hydroponic Nutrient Solution on Plant Growth, Nutrient Uptake, and Root Rot Disease Incidence of Basil (Ocimum basilicum L.)

Rootzone pH affects nutrient availability for plants. Hydroponic leafy greens are grown in nutrient solutions with pH 5.5 to 6.5. Lower pH may inhibit plant growth, whereas pathogenic oomycete growth and reproduction may be mitigated. General understanding of pH effects on nutrient availability suggests likely toxicity and deficiency of specific micronutrients. We hypothesized that if adjustments are made to the micronutrient concentrations in solution, plants will grow in lower-than-conventional pH without nutrient disorders, while oomycete disease incidence and severity may be reduced. To develop a new nutrient solution management strategy, we examined pH of 4.0, 4.5, 5.0, and 5.5 with or without micronutrient adjustments for growing two cultivars of basil plants Dolce Fresca and Nufar in a greenhouse hydroponic deep-water culture (DWC) system. Micronutrient adjustments included reduced concentrations of copper, zinc, manganese, and boron by one-half and doubled molybdenum concentration. Plants harvested 20 to 28 days after transplanting did not show significant effects of pH or the micronutrient adjustment. Phosphorus, calcium, magnesium, sulfur, boron, manganese, and zinc concentrations in leaves significantly declined, while potassium and aluminum concentrations increased with decreasing pH. However, these changes and therefore micronutrient adjustments did not affect basil plant growth significantly. ‘Nufar’ basil plants were then grown in a growth chamber DWC system at pH 4.0 or a conventional 5.5 with and without inoculation of Pythium aphanidermatum zoospores. Fourteen days after inoculation, P. aphanidermatum oospore production was confirmed only for the inoculated plants in pH 5.5 solution, where a significant reduction of plant growth was observed. The results of the present study indicate that maintaining nutrient solution pH at 4.0 can effectively suppress the severity of root rot caused by P. aphanidermatum initiated by zoospore inoculation without influencing basil growth.

Biogas digestates are not an effective nutrient solution for hydroponic tomato (Lycopersicon esculentum L.) production under a deep water culture system

The generation of energy through anaerobic digestion using animal manures is being promoted as an environmentally sustainable method of managing animal wastes. However, sustainability of biogas production is reliant on the sustainable utilization of the digestates that emanate from the process. Our study evaluated the effects of the biogas digestates on crop phytotoxicity and their fertilizer potential as a nutrient solution in hydroponic tomato production. Biogas digestates diluted up to 40% (v/v) resulted in significantly (P < 0.05) the lowest relative seed germination (RSG) in all vegetables evaluated in our study. The highest RSG was observed in the 10% biogas digestates, which was higher than the control treatment. For the crop growth study, relative to the control,the treatments with 20%, 40% and 60% mineral fertilizer substitution resulted in 39.4%; 22.8% and 8.7% significantly (P < 0.05) lower chlorophyll content, respectively. On average, the treatments with biogas slurry, though substituted with mineral fertilizers, resulted in a 275% lower fresh fruit yield compared to the control treatment. However, with biogas digestates, the sugar content in the tomato fruits significantly increased, whilst the heavy metal content was below that recommended limit when irrigation water is used. The results of our study demonstrated that cow based digestates are not a suitable nutrient media for hydroponic tomato production. Moreover, even with mineral fertilizer supplementation, only the control treatment containing only mineral hydroponic fertilizer resulted in positive growth and yield in tomatoes.

Aquaponics: a sustainable alternative to conventional agriculture in Egypt - a pilot scale investigation.

Conventional agriculture has been widely used to overcome food scarcity in Egypt, but in turn created new environmental, social, and economic problems. Aquaponics has a huge potential as a sustainable solution since it demonstrates promising results for urban food development while providing new entrepreneurship and start-up opportunities. Although it presents a big opportunity especially for developing countries like Egypt, it still requires further studies and researches to fully overcome foreseen challenges. This study discusses the possibility of implementing aquaponics as an alternative to conventional agriculture in Egypt through a comparison between aquaponics and conventional agriculture. The first section of this investigation analyzes the economic feasibility of aquaponics in terms of capital and operational expenditure costs. Then, an experimental comparative study is carried out examining two pilot-scale aquaponics systems (Deep water Culture system and Integrated Aqua-Vegaculture system), where crop quality (vitamins, heavy metals, and pesticides residues) of the two systems has been compared among each other, as well as to that of the commercially available organic food available in supermarkets. Results indicated that both systems produce high-quality safe organic food. The economic feasibility analysis indicated that Integrated Aqua-Vegaculture System is producing more crops with a wider variety of almost 20% less capital expenditure and operational expenditure costs. Fish production for both systems was close, yet slightly higher in Deep Water Culture. Although, on the short term, aquaponics entails relatively high capital and operational expenditure costs compared with conventional agriculture; yet, on the long term, it is more profitable, while saving up to 85% of the water wasted by conventional farming techniques. Finally, the study discusses the main limitations, drawbacks, and future of aquaponics in Egypt where public awareness and a new mindset are needed to highlight the link between agriculture and sustainability.

First Report of Pythium dissotocum Causing Pythium Root Rot on Hydroponically Grown Lettuce in Connecticut

In August 2016, lettuce (Lactuca sativa L.) plants presented root rot, severe wilting, and high incidence of mortality in New Haven County, CT. The plants were grown in a hydroponic deep-water culture system in a commercial greenhouse. Mature plants were stunted, the lower leaves were chlorotic, the roots were necrotic, and some plants collapsed. Lettuce roots were collected from several symptomatic plants, washed three times with sterile deionized water, blotted dry, and plated on PARP-V8 selective medium (0.005 g of pimarcin, 0.25 mg of ampicillin, 0.01 g of rifampicin, 0.10 g of pentachloronitrobenzene, 200 ml of clarified V8 juice, and 800 ml of distilled water) (Moorman et al. 2002). The plates were incubated in the dark at 21°C. Mycelium resembling the morphology of Pythium species was observed in all plates after 3 days. The isolate was identified as Pythium dissotocum based on the morphology of sexual and asexual structures following van der Plaats-Niterink’s key (van der Plaats-Niterink 1981). Colonies grown on V8-juice agar had filamentous sporangia with a dendroid structure, the oogonia were 23 μm in diameter and subglobose, the antheridia developed on unbranched stalks and were sessile, and the oospores were aplerotic. DNA was extracted from mycelial mats using a DNeasy Plant Mini Kit (Qiagen, U.S.A.), and the internal transcribed spacer (ITS) region was amplified using universal primers ITS1 and ITS4 (White et al. 1990). BLAST nucleotide analyses against publicly available Pythium sequences in GenBank confirmed that the isolates obtained were P. dissotocum with 97% query coverage and 99% identity match to GenBank accession number KM061701.1. The nucleotide sequence has been assigned the GenBank accession number MG993546. To confirm Koch’s postulates, 14-day-old lettuce seedlings, cultivar Rex (n = 25), were inoculated with 1 × 10⁵ zoospores of the isolate of P. dissotocum produced on V8 broth. After 7 days, symptoms appeared as reduced growth, necrotic roots, and chlorotic leaves. Control plants were symptomless and healthy. Roots were collected from each infected lettuce plant, and four root fragments were plated on PARP-V8 selective medium. Mycelial growth resembling Pythium was observed in all plates from inoculated plants, and no growth was observed from roots of noninoculated plants (n = 25, 1 plate per plant). The putative P. dissotocum was reisolated from the plates; DNA was extracted from mycelial mats using the same methods described above and was confirmed to be Pythium using primers ITS1 and ITS4. The amplicon was the same size as for the P. dissotocum recovered from the original plants. This is the first report of P. dissotocum being detected on lettuce in Connecticut. P. dissotocum reduces crop yield and was first reported in 1986 as a root pathogen on hydroponic lettuce in Arizona (Stanghellini and Kronland 1986). There are currently no registered synthetic-chemical fungicides in the United States for the suppression of Pythium species in hydroponic lettuce (Utkhede et al. 2009). Prevention of this disease is recommended by controlling temperature and salt levels in the nutrient solution, sanitizing surfaces, and applying preventative biological fungicides registered for Pythium root rot.