Recirculating Nutrient Solution Research Articles

Produção de agrião hidropônico por meio de reuso de água em piscicultura e tempos variados de recirculação de soluções nutritivas

ABSTRACT Aiming at a more sustainable food production, the reuse of effluent from fish farming in hydroponics can be a viable option. Thus, the objective of present study was to evaluate the effects of the use of effluent from fish farming on the development of ‘Folha Larga’ watercress and the possibility of reducing the use of fertilizer in a hydroponic system. The assay was carried out in a greenhouse from October 2021 to February 2022 (two cycles). The treatments were distributed in randomized blocks, with four replications, with split plots, consisting of two times of recirculation of the solution in the plots (T1 = 15 min operating by 15 min off and T2 = 15 min operating by 30 min off) and five solutions, in the subplots, obtained by mixing different proportions (0, 25, 50, 75, and 100%) of nutrient solution and effluent from fish farming. The variables analyzed were: plant height, number of leaflets, leaf area, SPAD index, fresh and dry weight of the aerial part and roots. The use of effluent from fish farming reduces the amount of fertilizers for the yield of ‘Folha Larga’ watercress. Nutrient solution recirculation time of 15 minutes is suitable for hydroponic watercress.

Nutrient Solution from Aqueous Extracts as an Alternative to Fertigation in Hydroponic

The reintegration of agro-waste into the same agriculture site fulfils the objective of the European Bio-Economy Strategy: to reduce transport costs, waste volume, and the need for mineral fertilizers. One of the fundamental principles in sustainable agriculture is the recycling of crop residues through composting or vermicomposting. From this process, it is possible to obtain organic matter for the production of aqueous extracts (tea) that can be used as a source of nutrients in fertigation as an alternative to mineral fertilizers. The objective of this research was to evaluate the use of an aerated or non-aerated aqueous extract as a recirculating nutrient solution in a hydroponic culture (NFT) of lettuce. For this, the test method was compared to hydroponic cultivation with a conventional nutrient solution. The conventional nutrient solution contained minerals or synthetic fertilizers and the aqueous extracts of vermicompost from vegetal residues of horticultural crops. The evolution of the chemical composition of the nutrient solutions during cultivation was analyzed, obtaining adequate concentrations of NO3−, K+, and Ca2+ and taking possible imbalances in nutrients such as P-H2PO4− into consideration. Plants fertigated with an organic and aerated nutrient solution obtained good yields and improvements in quality by having six times less N-NO3− in edible leaves compared to plants exposed to the mineral treatment. The preparation of aqueous extracts as a source of nutrients opens the door to circular agriculture to make processes in intensive production systems more efficient.

Current perspective on nutrient solution management strategies to improve the nutrient and water use efficiency in hydroponic systems

Hydroponics, a soilless cultivation technique using nutrient solutions under controlled conditions, is used for growing vegetables, high-value crops, and flowers. It produces significantly higher yields compared to conventional agriculture despite its higher energy consumption. The success of a hydroponic system relies on the composition of the nutrient solution, which contains all the essential mineral elements necessary for optimal plant growth and high yield. This review delves into the discussion of enhancing nutrient solution management strategies across different hydroponic systems. The aim of this review is to discuss various techniques for monitoring nutrient solutions in order to improve nutrient use efficiency (NUE) and water use efficiency (WUE). The conventional approach of monitoring the hydroponic nutrient solution using electrical conductivity measurement may not provide precise information about ion concentrations, potentially resulting in poor yields or excessive fertilizer usage. To overcome these limitations, alternative management strategies have been developed to enable more accurate monitoring and efficient management. One such strategy is the nitrogen-based approach, where nitrogen concentration becomes the primary controlled element in the nutrient solution and leads to WUE and NUE development by prolonging nutrient solution recirculation. Furthermore, various methods have been devised to improve nutrient solution strategies. These include using ion-selective electrodes to measure individual ions in the hydroponic nutrient solution, using sensors to monitor substrate moisture content, estimating water requirements, and implementing programmed nutrient addition methods. In addition to introducing different management techniques to optimize hydroponic performance, this review provides a better understanding of hydroponic systems.

Intervalo de recirculação da solução nutritiva na aclimatização hidropônica de mudas de bananeira

ABSTRACT The objective of this study was to evaluate the technical viability of using longer recirculation intervals of nutrient solution than those conventionally used for the acclimatization of Prata-Ana banana seedlings grown under hydroponic system. The experiment was carried out in a greenhouse of a banana plantlet production biofactory, in Cruz das Almas, Bahia, Brazil, in a randomized block design with four replications. The use of longer recirculation intervals of nutrient solution (0.75, 3.75, 5.75, 11.75, and 23.75 hours) than those commonly used for vegetables (0.25 hour) was evaluated in the present study in two seasons: winter and summer-autumn. The effect of increasing the interval of nutrient solution recirculation on plant growth was more pronounced when the temperature was higher, during the summer-autumn season. Considering the plant growth period between 15 and 20 days after transplanting, there was no effect of the recirculation frequency, showing the viability of using lower recirculation frequencies or only one recirculation per day in the first 15 days of plant growth. However, the use of shorter intervals after this period is needed because the use of intervals equal to or higher than 0.75 hour decreased plant growth in both seasons. Thus, the use of a 23.75-hour interval in the first 15 days and a 0.25-hour interval after this period allows a decrease in energy consumption, compared to the use of a 0.25-hour interval during the whole plant cycle.

Effect of Salicylic Acid on the Growth and Development of Sweet Pepper (Capsicum annum L.) under Standard and High EC Nutrient Solution in Aeroponic Cultivation

High electrical conductivity (EC) in cultivation systems with the recirculating nutrient solutions can affect plant growth and development. This study aimed to investigate the effect of salicylic acid (SA) on the selected physiological and biochemical parameters of sweet pepper (Capsicum annum L.) growing aeroponically at standard and high concentrations of nutritive solutions. Four experimental variants were tested: (1) plants cultivated under low EC conditions, (2) plants cultivated under low EC conditions and treated with foliar SA, (3) plants cultivated under high EC conditions, (4) plants cultivated under high EC conditions and treated with SA on leaves and roots. The obtained results revealed that exogenous SA, regardless of EC, reduced the formation of fruits with calcium deficiency symptoms. Furthermore, SA helps plants to cope with high EC nutrient stress through an increase in leaf SPAD index, maximum light-adapted chlorophyll fluorescence and PSII viability. Exogenous SA reduced the number of soluble proteins both under low and high EC; however, increased H2O2 content induced a defence mechanism reflected by the upregulation of antioxidant enzyme activity. The results of the study provide valuable information on the role of SA in the alleviation of the harmful effect of salinity under aeroponic cultivation.

Response of Ozone Treatment on Disease Incidence, Dissolved Oxygen Levels, Growth and Yield of Cucumber Crop Grown in Hydroponics in Cooled Green House. Season: Summer (June-August) at DGALR, Rumais

One of the main concerns related to closed systems is the potential spread of root pathogens. With the recirculation of nutrient solutions. Ozone treatment was tested for the efficacy against plant pathogen (Pythium), growth and yield of cucumber crop grown in hydroponic closed system during summer season (June-August) 2022. Two nutrient solution feeding tanks were used one with ozone treatment and other without ozone treatment in randomized complete design (RCD) with four replication. The results showed significant (p < 0.05) differences were observed between the treatments in diseases infections with pythium diseases. No significant (p < 0.05) differences were detected in chlorophyll content, as SPAD values and yield between the two treatment of cucumber statistically. Ozone treated plants produced more yield 4.0 ton/gh.

Growth of Hydroponic Sweet Basil (O. basilicum L.) Using Plasma-Activated Nutrient Solution (PANS)

Hydroponic sweet basil (O. basilicum L.) farming uses a recirculating nutrient solution that may spread waterborne microbial contamination including algae. Plasma, the fourth state of matter, generates antimicrobial reactive oxygen and nitrogen species when exposed to water. The objective of this work was to study the effect of plasma-treated water-based nutrient solution on plant growth and in reduction of algae. Basil plants were grown in isolated ebb and flow hydroponic systems (under monitored environmental conditions) using nutrient solution (NS) and plasma-activated nutrient solution (PANS) with two separate treatments: the same irrigation solutions were used in the growth cycle (Treatment 1: NST1 and PANST1 once at the beginning growth cycle) and new irrigation solutions at every week of the growth cycle (Treatment 2: NST2 and PANST2). The plant growth parameters (height, fresh and dry weight, number of branches and nodes, root length, leaf index), quality parameters (color, texture, aroma, and tissue nutrients concentration), and algae concentrations were measured. Compared to NST1, plants grown on PANST1 were significantly taller (up to 12%), had a higher fresh mass (up to 29%) and dry mass (up to 45%), and had a higher greenness value (up to 28%). Algae growth was significantly reduced in the PANST2 reservoir (up to 24%) compared to the NST2 reservoir. It was confirmed that Treatment 1 significantly improved the yield, morphology, and quality of sweet basil plants, while Treatment 2 was best suited to decreasing algae concentration in the hydroponic environment. This preliminary study indicated that PANS could improve the quality and growth of sweet basil in hydroponic farming while controlling the algae growth in the growing environment.

ANALYSIS OF EXISTING ENERGY INSTALLATIONS FOR ULTRAVIOLET DISINFECTION OF RECIRCULATING NUTRIENT SOLUTION IN SYSTEMS OF CROPS AUTOMATIC HYDROPONIC IRRIGATION IN PROTECTED GROUND

Decisive for solving food security problems in Ukraine while preserving and restoring the ecology of the environment should be an intensive method of management, i.e. the orientation of economic entities of their own activities on the innovative type of development, active use of scientific and technical developments and implementation of modern agricultural innovations. In its turn, the qualitative and quantitative indicators of crop production of protected soil depend on the technical condition of technological equipment.
 The purpose of the work is research and analysis of existing power plants for ultraviolet disinfection of recirculating nutrient solution in systems of automatic hydroponic irrigation of crops in a protected soil, as well as elucidation of the impact of filtration and disinfection of nutrient solution on the presence of microorganisms when reusing plants in systems. The paper investigates the ways to improve the operation of power plants for ultraviolet disinfection of recirculating nutrient solution in the cultivation of crop products of protected soil. It provides the value of the required radiation dose for 90% disinfection of the recirculation solution from various bacteria, viruses and fungal spores and the dependence of bactericidal efficiency on the wavelength of light. Ultraviolet rays with a length from 200 to 280 nm (UV-C range) have the most pronounced bactericidal effect. Research in this area has shown that the optimal wavelength for irradiation is 253.7 nm. As a result of such irradiation, microorganisms die or lose their ability to reproduce. It has been proven that the classical layout scheme of power plants for ultraviolet disinfection of the recirculation solution is inefficient, because it does not rid the recirculation solution of turbidity and the presence of iron and does not guarantee high efficiency of the ultraviolet disinfection plants. The paper describes the method of carbonate precipitation of metal ions, which is based on the formation of insoluble metal compounds as a result of treatment of an aqueous solution with carbonates or bicarbonates of alkali metals. Prospects for further research are the development of methods and tools to improve the operation of power plants for ultraviolet disinfection of recirculating nutrient solution in the cultivation of crop products of protected soil.

Prevention of Phytotoxic Effects of Regenerative In Situ Electrochemical Hypochlorination in Recirculating Hydroponic Systems

Recirculating nutrient solutions were treated using dimensionally stable anode (DSA)-based regenerative in situ electrochemical hypochlorination (RisEHc) in a deep water culture hydroponic lettuce (Lactuca sativa) production system. Phytotoxic effects were noted and attributed to the formation of chloramines in treated nutrient solutions containing ammonium. The presence of chloramines resulted in a decrease in overhead biomass by 53% using 2.27 mA/cm2 and 83% with 4.55 mA/cm2. Adding ultraviolet light as a tertiary treatment stage allowed the photodecomposition of chloramines, which prevented phytotoxicity in crops and caused no significant differences in growth between treatments. Furthermore, using a nitrate-based fertilizer also served to prevent phytotoxic effects in crops and showed no significant differences in growth between the control and 4.55 mA/cm2. In addition, it was found that the electrochemical flow cell (EFC) treatment resulted in a 13% increase in shoot biomass using 2.27 mA/cm2. The study demonstrated that phytotoxic effects can be prevented with the use of regenerative in situ hypochlorination through proper management and monitoring techniques in recirculating hydroponic systems.

Conditioners for raw rice husk substrate to produce strawberry transplants

The need to produce domestic strawberry transplants leads to the search for low-cost cultivation media in Brazil. Raw rice husk (CAIN) is an abundant and economical material in the south of the country. This study aimed to evaluate three substrate conditioners (35%) [carbonized rice husk (CRH), vermiculite and the commercial substrate S10®] added to RRH (65%) and their effects on growth, production and quality of strawberry transplants grown on benches with recirculation of nutrient solution, in a greenhouse. The experimental design was in causal blocks with three treatments and four replicates. Two mother plants of the Aromas cultivar were grown on each plot between November/2016 and March/2017. Transplants were classified into groups according to crown diameter (Class 1: 3.0-5.0 mm; Class 2: 5.1-8.0 mm; Class 3: >8.1 mm). Similarly, the number of leaves, leaf surface, fresh and dry mass of leaves and crowns of 10 transplants belonging to each class were evaluated. With the addition of CAC and vermiculite to the substrate, the predominance of class 2 transplants was obtained. The addition of S10 to CAIN increased the total number of transplants, as well as the number of leaf surface transplants and the dry mass of the aerial part of plants, in class 3 transplants, as well as S10 and vermiculite, provided a greater number of propagules produced.

Response of Ozone Treatment on Dissolved Oxygen Levels, Growth and Yield of Cucumber Crop Grown in Hydroponics in Cooled Green House. Season: Winter (December-March)

One of the main concerns related to closed systems is the potential spread of root pathogens. With the recirculation of nutrient solutions, ozone treatment was tested for the efficacy against plant pathogen (Pythium), dissolved oxygen levels, growth and yield of cucumber crop in hydroponic closed system during December-March 2020/21. Two nutrient solution feeding tank were used one with ozone treated and other without ozone treated in randomized complete design (RCD) with four replication. The results showed that no plants were affected with pythium diseases in both treatments Ozone treated and untreated during winter season. Significant (p < 0.05) differences were observed in chlorophyll content, as SPAD values between the two treatments and their interactions in cucumber. Also, no significant differences were observed in yield between the two treatments.

The effect of different fertigation strategies on salinity and nutrient dynamics of cherry tomato grown in a gutter subirrigation system

The advantages of subirrigation for water distribution uniformity, water-saving, and other crop performances have been well documented in previous works. However, in subirrigated crops, an accumulation of salts inevitably occurs in the top layer of the growing medium, which represents one of the main difficulties to prolong the recirculation of the nutrient solution. Such an accumulation strongly depends on nutrient and non-nutrient (e.g., saline ions) concentrations, irrigation scheduling and water volumes and fluxes in the system. Tomato cherry plants (Solanum lycopersicum L. cv. Shiren) were grown soilless in a gutter subirrigation (closed-loop) system, during the spring season, to evaluate nutrient dynamics and crop response to: i) the nutrient solution concentration (i.e., standard and 50% reduced concentration), ii) irrigation frequency (i.e., high or low frequency), iii) irrigation duration (i.e., long or short time duration), and iv) tank volume at the refill (i.e., high and low volume). The most important factor, which influenced the nutrient dynamics and electrical conductivity of the system, was the concentration of the nutrient solution, followed at distance by the other three. The recirculated solution with reduced concentration showed a fairly stable composition (ranging from 1.2 to 1.6 dS m−1 of the electrical conductivity in the worst factor combination) with the electrical conductivity of water extracts in the upper substrate layers below 2.0 dS m−1 and the ratio between recirculated solution and plant uptake concentration of about 1 for most of the elements. Marketable fruit yield was 48% higher with the reduced concentration solution and affected by irrigation scheduling and tank volume at refill. By adapting the composition of the recirculated nutrient solution, to the available water quality and plant needs, a gutter subirrigation closed system can be safely managed for a short-cycle spring tomato crop.

Nitrate supply limitations in tomato crops grown in a chloride-amended recirculating nutrient solution

Partial substitution of nitrate (NO3-) with chloride (Cl-) in the nutrient solution supplied to tomato crops (beefsteak and cherry types), grown in a closed hydroponic system, maintained nitrogen (N)- and carbon (C)- assimilation status in plants despite N-supply limitations. Lowering NO3- ions (90% of total N) supply to 2/3 of the standard recommendations, which was electrochemically compensated for by an equivalent increase of the Cl- concentration in the replenishment nutrient solution (RNS), increased N use efficiency (kg produce kg−1 N supply) and decreased NO3- in the drainage without compromising growth, yield and nutritional quality. Tomato plants supplied with Cl--amended RNS increased leaf Cl- content to macronutrient level (35 mg g−1 dry weight), retaining photosynthetic rates and crop yield potential at lower stomatal conductivity and transpiration. Nutrient to water uptake ratios (mass of nutrient per water volume absorbed), which are commonly termed ‘uptake concentrations’, were defined in different cropping seasons and ranged as follows: 12.1–13.5 (Nitrogen- NO3-+NH4+), 1.25–1.35 (Phosphorus-P), 6.1–6.3 (Potassium-K), 3.6–4.0 (Calcium-Ca), 1.0–1.3 (Magnesium-Mg, mmol L−1), 13.0–14.3 (Iron-Fe), 7.6–8.4 (Manganese-Mn), 5.1–5.2 (Zinc-Zn) and 0.7–0.9 (Copper-Cu, μmol L−1). The levels of N and Cl- supply had no impact on the uptake concentrations. This study suggests that replacing 1/3 of the standard NO3- supply by Cl- in closed hydroponic tomato crops enhances N use by two-fold and eliminates NO3- losses to one-half, with no significant effects on assimilation processes and fruit biomass production, suggesting that Cl- at appropriate concentrations is not only an essential micronutrient but also a beneficial macronutrient. The obtained uptake concentrations may be used through on-line operating decision support systems to optimize nutrient supply in hydroponic cultivations in Mediterranean greenhouses.

Development of a robust nitrate sensor for online measurements

According to the EU Water Framework Directive the emission of nutrients and plant protection products to water bodies should be reduced dramatically. In practice threshold values for water bodies are exceeded due to leakages, discharges and unexpected problems from greenhouse facilities. Nitrate eutrophicates surface water. In the Netherlands nutrient solution recirculation in soilless cultivation is obliged and discharge is regulated to yearly crop specific nitrogen concentrations. However, water authorities still measure exceedances in surface water, leading to an interest real-time measurement of nitrogen or nitrate to have data faster available. Adjustments in nutrient recipes in greenhouses are based on a 7-14 days analysis of drainwater by sending it to a laboratory. This practice is suboptimal since the loss in nutrients is higher than necessary and it might even reduce crop development. Besides it is time consuming and often expensive. In areas where the results of the laboratory are not fast available, a nitrate sensor may even play an important role in creating the right solution for the plants. With a real-time measuring nitrate sensor, it is possible to fertigate more accurately which increases the harvest/quality of the crop with a lower environmental footprint. Besides, such a nitrate sensor has also a large scientific value since the dynamic nitrate uptake by the crop can be studied at a scale of minutes instead of days. A start has been made to analyse available methods for measuring nitrate, and in this study we will present an innovative optical fibre based nitrate sensor using an algorithm which has been tested in a greenhouse setting at field conditions. This UV-VIS spectroscopy system in combination with the developed model can be used for online monitoring of nitrate concentrations in hydroponic solutions, without the use of any reagents or need for recalibration, to enhance the efficiency and safety of greenhouse systems with respect to water reuse and recycling.

Sensor-Based Nutrient Recirculation for Aeroponic Lettuce Cultivation

The objective of this study was to investigate the effects of used-nutrient solution recirculation on nutrient efficiency improvement and reduction of environmental pollution of an ion-selective electrodes (ISEs)-based recycle-type aeroponic crop cultivation system. A recycle-type aeroponic crop cultivation test bench was fabricated, which consisted of K+, NO3-, and Ca2+ ISEs, pH, and EC sensor, and lettuce were cultivated for inspecting the nutrient solution recirculation process. The specific growth rate of lettuce was evaluated. Different percentages of the used-solution (20%, 40%, 60%, 80%, and 100% of the target volume) were recirculated to find a proper recirculation volume for maintaining the target nutrient level with the minimum supply of stock solutions. The nutrient saving percentage was determined by comparing the nutrient solution requirement with the open-type aeroponic system and open-field cultivation practices. Reduction of environmental pollution was assessed based on the possible environmental pollutions (i.e., surface water pollution, groundwater contamination, and contaminant deposition in the human body), which could be occurred by the direct discharge of the hydroponic nutrient solution. The minimum amount of stock solutions were required during the 60% used-solution recirculation. The nutrient solution requirement of the recycle-type aeroponic system was almost 3 to 5 times less than the open-type aeroponic system, and 3 to 6 times less than open-field cultivation based on nutrient consumption rates at different growth stages. An open-type aeroponic system might require more nutrient solution than the open-field cultivation practices based on the frequency of nutrient solution supply in the crop root zone. Although, the discharged nutrient solution increased the K+, NO3-, and Ca2+ ion levels a little in the considered surface water reservoir, groundwater, and human body, long-term discharge of the high concentrated hydroponic nutrient solution would be hazardous. The findings of this study showed that the nutrient saving efficiency of a recycle-type crop cultivation system is higher compared to the open-type and conventional cultivation practices, which can minimize the cultivation cost notably, and the environmental pollutions can be reduced significantly through the sensor-based nutrient management.

Biomass production and essential oil content and composition in basil hydroponic systems using treated domestic effluents

Reusing domestic wastewater is an alternative for irrigated agriculture, helping to decrease pressure on good quality water. This study aimed to evaluate the biomass production and essential oil content and composition in the basil genotypes ‘Alfavaca Basilicão’ and ‘Grecco a Palla’ with different plant spacing in hydroponic systems. Two experiments were carried out between March and May (Experiment I) and July and September of 2015 (Experiment II) in a completely randomized design with four replicates in a 2×3 factorial arrangement. In Experiment I, two hydroponic systems (Laminar Nutrient Flow Technique - NFT and Deep Nutrient Flow Technique - DFT) and three plant spacings in hydroponic channels (0.20, 0.30, and 0.40 m) were evaluated. In Experiment II in the DFT hydroponic system, two types of water (tap water and treated domestic effluents) and three nutrient solution recirculation intervals (at intervals of 2, 4, and 6 h) were evaluated. In general, the dry biomass per plant, oil content and oil yield of the two basil genotypes were not influenced by the hydroponic systems, plant spacing, or water type. In Experiment II, the increase between the recirculation intervals (4 or 6 h) negatively affected genotype ‘Grecco a Palla’. Linalool was the major constituent in the essential oil of the two basil genotypes, ranging from 47.00 to 70.10% (Experiment I) and from 59.47 to 63.64% (Experiment II) in genotype ‘Alfavaca Basilicão’; in genotype ‘Grecco a Palla’, it ranged from 10.19 to 43.03% (Experiment I) and from 19.94 to 53.37% (Experiment II).

Fruit production and quality of mini-watermelon with different number of stems, in troughs cultivation system and substrate reuse

Substrate-filled pots are growing systems commonly used for vegetable farming. However, few are the studies available relating them to mini-watermelon cultivation. Our study presents a growing system using substrate-filled troughs and leachate recirculation as a low-cost and less environmentally harmful soilless cultivation system for mini-watermelons. For a growing system to be viable and provide high fruit yield and quality, several aspects must be studied, including substrate physical properties and reuse potential in successive crops, besides plant management-related aspects. Therefore, our goal was to evaluate the effects of a trough system and substrate reuse on changes in the properties of raw rice husk and on fruit yield and quality for mini-watermelons at different stem training. To this purpose, two trials were conducted using nutrient solution recirculation systems. In the first, we evaluated the effects of pot and trough systems. In the second, first- and second-use substrates were compared in the trough system. In both trials, one and two-stem training systems were analyzed. The results of the first trial show that the trough system had a greater positive impact on substrate water holding capacity (WHC), which increased from 7.9 to 15.6%, while the pots increased substrate WHC only to 11.2%. However, both systems neither affected fruit yield (8 kg/m² on average) nor fruit quality. The two-stem training promoted higher fruit yields (4.2 kg/plant) and contents of total soluble solids - TSS (11.4 °Brix) but did not affect average fruit weight. Moreover, the one-stem training provided higher fruit number (7.3 fruits/m²) and fruit yield (9.7 kg/m²). In the second trial, the reused substrate showed a higher WHC (12.4%) than the one used for the first time (9.9%). The reused substrate also provided better results in terms of fruit yield and quality (5.9 fruits/m², 5.3 kg/m², and 10.5o Brix). In the second trial, two-stem training also increased average fruit weight, and hence yields per plant. Nevertheless, the stem number did not affect fruit number per plant, fruit yield per square meter, and fruit quality.

NDT, a new soilless growing system without substrate suitable for Mediterranean conditions

Nutrient film technique (NFT) is characterized by the reduction of the dissolved oxygen concentration (DOC) in the recirculating nutrient solution along the gully; this is most intense in warm climates like the Mediterranean region. In this case, plant’s roots at the end of gully suffer from oxygen deficiency. The aim of this study was to develop a new soilless system without substrate which eliminates this NFT drawback and the cost of the substrate. Therefore, a new soilless system was designed. This new system associated the continuous drip irrigation along the gully with the recirculation of the nutrient solution and it was defined as Nutrient Drip Technique (NDT). In addition, the root gully was modified and shaped as W to provide better drainage of the nutrient solution in NDT system compared to NFT system. This system was tested for a tomato crop and compared with an NFT system and for a cucumber crop and compared with a media-based perlite and an NFT system. DOC measurements were taken along the gullies of the different systems. The results indicated that DOC of the nutrient solution along the gullies of NDT was higher and more uniform compared to NFT. Both tomato and cucumber plants grown in NDT system had higher Leaf Area Index (LAI) and were more productive compared to the conventional NFT system. Cucumber crop in NDT system had similar growth and productivity as in the perlite system. Water Use Efficiency (WUE) was higher in NDT compared to NFT system. Consequently, NDT system provides a better control of the root environment and the independence of porous substrates.

Water Microbiota in Greenhouses With Soilless Cultures of Tomato by Metabarcoding and Culture-Dependent Approaches.

Water supply, in hydroponic greenhouses, can originate from groundwater, surface water or rainwater stored in open tanks. To limit contamination of water supply, several methods have been used including active and passive methods such as slow filtration techniques which consist in passing the nutrient solutions slowly through filters. The purpose of this study was to describe the microbiota associated with water sampled before entering greenhouses and in recirculating nutrient solutions, either before or after running through a biofiltration system. Metabarcoding analysis revealed that water ecosystems were unique niches for diverse bacterial and fungal communities. Microbial composition varied greatly across storage conditions (groundwater vs. rainwater) and among greenhouses, suggesting that water microbiota is site- and storage-condition-specific. Nonetheless, we found that microbiota structure in open-stored water (either coming from ground or rain) shared a higher degree of similarity than with water directly pumped out of the ground. Open-stored waters were characterized by predominant taxa, notably those involved in aerobic chemoheterotrophy, such as the Sphingomonadaceae and Hyphomicrobiaceae families. Water directly collected from the ground showed the lowest levels of fungal and bacterial richness while also characterized by a significantly higher level of bacterial equitability and an enrichment in taxa involved in N-cycling. Slow filtration allowed reducing cultivable bacterial loads as well Pythium spp. and Fusarium oxysporum propagules, based on culture-dependent results, without compromising microbiota richness and diversity. Although compositional structure was similar following biofiltration, significant differences in bacterial (but not fungal) taxa abundance were reported, with primarily an enrichment of Chelativorans, Mycobacterium, and Gemmata as well as a depletion of Rhodobacter, Aminobacter, and Ellin329. The exact mechanisms by which such taxa would be favored at the expense of other remained unknown. Besides the accurate description of microbiota found in water at both taxonomical and predicted functional levels, our study allowed comparing the water microbiota between various storage system and following biofiltration. Although preliminary, our results provide a first insight into the potential microbial diversity, which can increase ecosystem functionality.

Dynamic changes in bacterial communities in the recirculating nutrient solution of cucumber plug seedlings cultivated in an ebb-and-flow subirrigation system.

Ebb-and-flow subirrigation systems are highly efficient, water-saving and environmentally friendly. However, one concern with these recirculating systems is the possible transmission of plant pathogens. Here, through 16S rRNA-targeted Illumina sequencing, the bacterial dynamics in a recirculating nutrient solution were characterized for cucumber plug seedlings cultivated in an ebb-and-flow system in summer and winter. Both the bacterial number and diversity in the nutrient solution increased immediately after the first irrigation cycle; then, these values were gradually stable with recirculating irrigation. In summer and winter, different bacterial compositions and changing patterns were observed. In summer, the predominant genera in the nutrient solution included Comamonas, Pseudomonas, Acinetobacter, Reyranella, Sphingobium, Bradyrhizobium, Sphingomonas, and Acidovorax. Of those genera, during recirculating irrigation, the relative abundance of Bradyrhizobium gradually decreased, whereas those of Pseudomonas, Reyranella, Sphingobium, Sphingomonas, and Acidovorax gradually increased. In winter, the bacterial communities were mainly composed of Nevskia, Bosea, Sphingobium, Acidovorax, Pseudomonas, and Hydrocarboniphaga. Of those genera, the relative abundance of Bosea, Sphingobium, and Acidovorax showed an increasing trend, whereas those of Nevskia and Hydrocarboniphaga decreased overall. Furthermore, in both summer and winter, no plant pathogenic bacteria on cucumber could be detected; however, some potentially beneficial bacteria, including Comamonas testosteroni, Acinetobacter baumannii, Pseudomonas aeruginosa, P. koreensis and Sphingobium yanoikuyae, colonized the nutrient solution and exhibited increased relative abundances during irrigation. The colonization of these bacteria might facilitate the plant growth promotion. Inoculation of the microbes from the effluent nutrient solution also promoted the growth of cucumber seedlings, but did not lead to any disease. The present data elucidate the bacterial dynamics in a cucumber cultivation ebb-and-flow system and provide useful information for biological control during cucumber seedling production.