Standard Nutrient Solution Research Articles

A Comparison of Plant Growth Rates between an NFT Hydroponic System and an NFT Aquaponic System

A comparison of leafy green plant species’ (lettuce (Lactuca sativa L.), dill (Anethum graveolens L.), rocket (Eruca sativa), coriander (Coriandrum sativum L.), and parsley (Petroselinum crispum)) growth rates was performed between an Nutrient Film Technique (NFT)hydroponic system, using standard commercial nutrient solution, and an NFT aquaponic system, using fish waste from Grass Carp, (Ctenopharyngodon idella) which provided the majority of the nutrients required by the plants. The results demonstrated that the aquaponic method performed well, and, in many cases, the growth rates produced were similar to those of the hydroponic method. Lettuce growth was compared across three seasons (summer, winter, and spring), and, in all cases, the aquaponically-grown lettuce equalled, or bettered, the hydroponic equivalent. Herb growth was compared over a five-month period (February to June—summer/autumn), and in 17 out of 23 comparisons, the aquaponic method produced results similar to those of the hydroponic method. Thus, while the NFT method may not be the most appropriate technical approach for aquaponic integration, the results suggest that the overall aquaponic method has the potential to produce plant growth rates at least equal to those of standard hydroponics.

Effects of the electrical conductivity of a soilless culture system on gamma linolenic acid levels in borage seed oil.

Borage is a well-known plant of great importance in human nutrition and health. Expanding knowledge of particular plants that have anti-cancer products is a global concern. There is substantial information regarding the benefits, presence and extraction of gamma linolenic acid (GLA; 18:3n6) in different plants around the world, especially in borage seeds. However, there is little information concerning the effects of the salinity of the nutrient solution on the growth and presence of GLA in borage seeds. The objective of this work was to determine the optimal salinity of the nutrient solution for obtaining GLA in soilless cultivation systems. Borage plants were grown in coconut fibre and provided three treatments of nutrient solution of 2.20, 3.35 and 4.50 dS m-1, increasing solution salinity with the standard nutrient solution of concentrated macronutrients as a reference. Vegetative growth, seed production and GLA ratio were measured. The results of vegetative development and GLA production doubled and tripled with the increase in salinity of the nutrient solution, respectively.

PRODUÇÃO E QUALIDADE DE FRUTOS DE PEPINEIRO EM DIFERENTES CONCENTRAÇÕES DE SOLUÇÃO NUTRITIVA

Cucumber is a vegetable crop widely consumed fresh and appreciated by a source of vitamins and minerals. It is a crop suitable for cultivation in protected environment, but little research has been carried out to improve the cultivation of this species under such conditions. Our aim was to evaluate the effects of different concentrations of nutrient solution on yield and fruit production and quality of cucumber grown in coconut fiber substrate. The experiment was conducted in greenhouse utilizing design in randomized block, with four replications and five plants per plot, were evaluated five concentrations of nutrient solution (12.5; 17; 25; 50 and 100% that after dilution resulted in electrical conductivities of 1.0, 1.2, 1.5, 2.3 and 3.8 dS m -1 , respectively). At 84 days after transplanting fruits of cucumber were harvested to evaluate yield and fruit quality. The reduction of nutrient concentration in the standard nutrient solution from 100% to 12.5% did not affect cucumber production. Biometric characteristics mean weight, longitudinal diameter, fruit storage thickness and titratable acidity are reduced as a function of the electrical conductivity of the nutrient solution from 1.0 to 3.8 dS m -1 . The concentration of nutrients in the solution was 67.5% of the standard nutrient solution, corresponding to 111.58 g of N-KNO 3 , 50.00 g of P-MAP, 62.44 g of K-KCl, 241.50 g of Ca-CaNO 3 and 120.00 g of Mg-MgSO 4 , provide satisfactory yield and better physical-chemical quality of cucumber fruits.

Development of an in vitro hydroponic culture system for wasabi nursery plant production—Effects of nutrient concentration and supporting material on plantlet growth

The growth of wasabi (Wasabia japonica Matsumura) plantlets was compared in four concentrations of standard Enshi nutrient solution (25%, 50%, 100%, and 150%) and two kinds of supporting materials (rockwool and vermiculite) using an in vitro hydroponic culture system for photoautotrophic micropropagation. After 28 days of culture, most of the growth parameters such as fresh weight and dry weight, shoot/root dry weight ratio, and leaf area ratio were highest in wasabi plantlets grown in 50% or 100% nutrient solution, and this enhancement was greater in vermiculite than in rockwool. Dissolved oxygen concentration decreased sharply in rockwool but only slightly in vermiculite during the course of the experiment, resulting in a dissolved oxygen concentration of 8 mg L−1 in the vermiculite and 6 mg L−1 in the rockwool. The highest root nitrogen concentration was observed at a nutrient concentration of 100% in vermiculite and rockwool. The highest net photosynthetic rates were observed on day 28 in vermiculite at nutrient concentrations of 50% and 100%. The growth of wasabi plantlets is depressed through a decrease in root water and nutrient uptake caused by low dissolved oxygen concentrations. These findings clearly demonstrate that a hydroponic system that incorporates a 50% or 100% nutrient solution concentration and vermiculite will allow high-quality wasabi plantlets to be propagated rapidly under photoautotrophic conditions.

Effect of Saline Stress and Calcium Nitrate on Lettuce Grown on Coconut Fiber

This study aimed to evaluate the use of saline solutions enriched with calcium nitrate in the production of lettuce grown in coconut fiber. The experiment was carried out from July to August 2017 in a greenhouse, at the Federal Rural University of the Semi-Arid Region (UFERSA), Mossoró-RN, Brazil. A randomized block design was used, in 2 × 5 factorial scheme, with three replicates. Treatments resulted from the combination of two lettuce cultivars [Elba (Curly) and Irene (Crisphead)] and five nutrient solutions (S1- standard nutrient solution; S2-S1 + NaCl (28.48 mmol L-1); S3-S2 + Ca(NO3)2 (6.89 mmol L-1); S4-S2 + Ca(NO3)2 (9.15 mmol L-1); S5-S2 + Ca(NO3)2 (11.43 mmol L-1)]. Plants were harvest 30 days after transplantation and the following variables were analyzed: head diameter, stem diameter, number of leaves, fresh weight, dry weight, leaf area, specific leaf area and leaf succulence. The cv. Irene (Crisphead) is more tolerant to nutrient solution salinity compared with the cv. Elba (Curly). Nutrient solutions enriched with 50 and 100% of Ca(NO3)2 promoted better performance of the cultivars Elba and Irene, respectively, fertigated with saline nutrient solution.

Electro-degradation of culture solution improves growth, yield and quality of strawberry plants grown in closed hydroponics

Strawberry plants grown in closed hydroponics accumulate root exudates and cause autotoxicity-a form of intra-specific allelopathy. Root exudate contains several allelochemicals and among them benzoic acid (BA) found as the most potent growth inhibitor. In this study, we applied electro-degradation (ED) to the culture solution in order to degrade their root exudates and improve growth, yield and quality of strawberry. There were four types of nutrient solution used in this study viz. renewed, non-renewed, non-renewed with direct current electro-degradation (DC-ED) and non-renewed with alternative current electro-degradation (AC-ED). Every three weeks interval, culture solutions were changed with fresh 25% standard Enshi nutrient solution in renewed treatment, while DC- and AC-ED treatment were applied in non-renewed solutions. Significantly greater fruit yield (225.9 g plant−1) was obtained from renewed nutrient solution, which was statistically similar to fruit yield in non-renewed solution with AC-ED application. Compared to renewed solution, fruit yield was decreased to about half (114.0 g plant−1) in non-renewed solution while non-renewed with DC-ED produced intermediate yield between non-renewed and renewed solution or non-renewed with AC-ED. In general, growth performance was greater in renewed solution followed by non-renewed with AC-ED, while it was decreased significantly in non-renewed solution with DC-ED similar to non-renewed solution. A similar trend was also observed in vitamin C content while brix and citric acidity was not varied. Minerals such as calcium and iron concentration in the culture solution were significantly decreased in DC-ED, consequently their contents were also found lower in crowns and roots compared to other solutions used. Therefore, it is evident that growth, yield and quality of strawberry can be improved through application of AC-ED in non-renewed solution.

Rosemary growth and nutrient balance: Leachate fertigation with leachates versus conventional fertigation

Abstract The free discharge of drainage water from greenhouse horticultural production to the environment is a current environmental concern due to its capacity to contribute to environmental pollution. This has led to the search of sustainable alternatives for its reuse in the production of other crops. However, before the large-scale use of such horticultural leachates in ornamental plants, the effects of such fertigation treatments on ornamental plants need to be evaluated. Plants of rosemary were grown in pots with a mixture of sphagnum peatmoss and Perlite and subjected to three fertigation treatments: T0 (a standard nutrient solution or control), T1 (raw leachates from Cucumis melo) and T2 (a mixture of raw leachates from C. melo and tap water 1:1 v/v, over a period of 9 weeks. At the end of the experiment, the growth parameters, color of leaves as well as water and nutrient uptake efficiencies and their losses were assessed for each fertigation treatment. The total dry weight and the water use efficiency of rosemary plants decreased under the fertigation with raw and diluted leachates. In addition, rosemary plants were shorter compared to the control but there were no differences in leaf color between the fertigation treatments. The uptake of N, P and K were affected by the applied fertigation treatments in a different manner. The use of horticultural leachates in the production of ornamental plants (as shown here for melon and rosemary) is feasible and presents a viable option to reduce water and nutrient input in plant production.

“Alperujo” Compost Improves the Ascorbate (Vitamin C) Content in Pepper (Capsicum annuum L.) Fruits and Influences Their Oxidative Metabolism

“Alperujo” compost was evaluated as an organic fertiliser for pepper growth under greenhouse conditions. Even though the total nitrogen applied was similar, plants only grown with composts experienced a development decline as compared to those grown with standard nutrient solution. This was perhaps because nitrogen from the compost was essentially organic, and not easily available for roots. When, alternatively, the compost was supplemented with nitrate, a synergetic effect was observed, favouring plant development and fruit yield, simultaneously with the increase of compost rates. Compost affected the oxidative metabolism of pepper plants by increasing their antioxidative enzyme activities catalase and superoxide dismutases and the non-enzymatic antioxidants ascorbate and glutathione. Overall, when nitrogen limitation occurred and only compost was used as fertiliser, an oxidative stress took place, whereas in plants grown with nitrate-supplemented compost it did not. Furthermore, these pepper plants experienced a yield increase and, more importantly, an enhancement of the ascorbate content.

Effect of cultivar and growing medium on the fruit quality attributes and antioxidant properties of tomato (Solanum lycopersicum L.)

The objective of this research was to identify the growing medium that yielded the highest nutritional quality and longest marketable shelf life in tomato fruits. ‘TY Megaton’ and ‘Yureka’ cultivars were grown on soil and coir pith in the same climate-controlled glasshouse using a standard nutrient solution and the recommended cultivation practices. Fruits were harvested at the pink stage of ripening and stored at 12 °C in 85 ± 5% relative humidity for 20 days. The fruits of both cultivars grown on either growing medium were of acceptable quality for sale after 3 weeks of storage. The contents of the most important secondary metabolites of tomato responsible for providing their antioxidant activity (ascorbic acid, lycopene, and polyphenols) were not significantly affected by the choice of growing medium; however, significant differences were observed between the cultivars throughout the storage period. The results of this study demonstrated that the choice of cultivar is more important for fruit quality than the growing medium. The lycopene content and antioxidant activity of the fruits suggest that it is possible to achieve optimum nutrition from the pink-stage fruit of both cultivars after 12 days of storage, irrespective of the growing medium used.

Cascade Cropping System with Horticultural and Ornamental Plants under Greenhouse Conditions

The blending of drainage with water of low electrical conductivity and the sequential reuse of the drainage water are innovative technologies to manage salts in agricultural drainage. Plants of Cucumis melo were grown in coir grow bags, and Rosmarinus officinalis and Cacti spp. were grown in pots with a mixture of sphagnum peat-moss and perlite. In order to assess the effect and evolution over time of these water treatments on plant growth and water management and removal of nutrients, three water treatments were applied over a period of eight weeks. These were: (1) standard nutrient solution; (2) blended water treatment (drainage water blended with water of low electrical conductivity (EC)) and (3) sequential reuse of drainage water treatment. During the experimental growing period, samples of water supplies and drainages generated in each water treatment were collected weekly and from these data water volume and nutrient loads were calculated. At the end of the experiment, leaf fresh weight of rosemary plants decreased under the fertigation with the blended and sequential reuse water treatments. Nevertheless, the application of blended and sequentially reused water allowed for the saving of significant amounts of water and nutrients in comparison to the standard nutrient solution treatment. Considering these advantages, we strongly recommend the setting-up of these water treatments in areas with water scarcity such as in the Mediterranean Basin.

Crop and Irrigation Management Systems under Greenhouse Conditions

Plants of Ruscus aculeatus, known as “butcher’s broom”, Maytenus senegalensis, known as “confetti tree”, and Juncus acutus, known as “spiny rush” were grown in pots with a mixture of sphagnum peat-moss and Perlite in order to determine the effect and evolution over time of three water use systems on plant growth, water saving and nutrient uptake. These were an open system (irrigated with standard nutrient solution) and two closed systems (blended-water (drainage water blended with water of low electrical conductivity (EC)) and sequential reuse of drainage (sequential-reuse) water), over a period of 8 weeks. Irrigation with blended- and sequential-reuse-water increased the biomass of all three species at the end of the experiment, compared to the open system. Overall, sequential-reuse-water treatment maximised biomass production. The application of blended- and sequential-reuse-water allowed savings of 17% of water in comparison to the open system. Regarding Cl, NO3− and H2PO4− loads, there was a removal of 5%, 32% and 32%; respectively in the blended-water treatment and 15%, 17% and 17% in the sequential-reuse water treatment compared to the open system. For the cation loads (Na+, K+, Ca2+ and Mg2+) in these water treatments there was a removal of 10%, 32%, 7% and 18% respectively in the blended-water treatment, and 17%, 22%, 17% and 18% respectively in the sequential-reuse treatment, compared to the open system.

Effect of planting and fertilization on lead partitioning in dredged sediment.

Dredging has been practiced to remove sediment impacted by persistent contaminants, such as heavy metals. Of these metals, lead (Pb) is of particular concern due to its toxicity. Therefore, dredged sediment containing Pb requires further mitigation. One method for Pb mitigation is phytoremediation of dredged sediment. In this study, the partitioning of Pb in sediment during phytoremediation by willow (Salix integra) was assessed. The results showed that, in general, the bioavailable forms of Pb declined with increased application of the standard Hoagland nutrient solution, which appeared to enhance the Fe-Mn oxide fraction and residual inert fraction. In contrast, the addition of excess phosphorus decreased the bioavailable fractions of Pb. However, the bioavailable fractions of Pb increased with additional potassium addition. Planting Salix integra was shown to promote the stabilization of Pb in sediment and led to a transformation from bioavailable forms to non-bioavailable forms. The results suggest that planting Salix integra can remediate Pb-contaminated dredged sediment via Pb immobilization by the roots. During this process, the application of Hoagland nutrient solution and the application of nutrient solutions with excess phosphorus not only promote root growth of Salix integra which would reduce Pb bioavailability, but also further enhance the immobilization of Pb in contaminated sediment, likely through the formation of Pb-containing compounds with low bioavailability.

Response of Container-grown Confetti Tree Irrigated with Runoff Water

This experiment measured plant growth of a halophyte (species adapted to saline conditions) confetti tree (Maytenus senegalensis) using runoff from kneeholy plants (Ruscus aculeatus). Three irrigation treatments were used, a standard nutrient solution or control (T0), runoff water collected from kneeholy plants irrigated with the standard nutrient solution blended 50:50 with tap water (T1), and 100% runoff water collected from kneeholy plants irrigated with the standard nutrient solution (T2), in which the nutrient concentrations were analyzed by high-performance liquid chromatography. Growth, photosynthetic parameters, and mineral composition were measured at the end of the experiment. Electrical conductivity and pH increased with increasing runoff application (decreased blending). Treatment 2 had significantly higher plant height, number of branches, number of leaves, leaf area index, and dry weight. Treatments 1 and 2 had significantly lower root lengths compared with the control. Chlorophyll concentration and green index color in leaves were greater in T2 and T1 than T0. The mineral composition of roots and leaves was affected by irrigation treatment, resulting in an increase of sodium and chloride concentration and a decline of nitrogen and phosphorous concentration compared with the control. The reuse of runoff water was beneficial for growing this commercially important halophytic species in Spain, a consideration that is particularly relevant in locations with water quality, quantity issues, or both.

Effect of ozone treatment and light colour on photosynthesis and yield of lettuce

Between factors which may influence on plant growth are light conditions and chemical composition of atmosphere. The objective of this study was to investigate the effect of ozone treatment (at the stage of seeds and seeds+seedlings, described as O3-I and O3-II) and light colour (white, blue, and white+blue 50:50) on photosynthesis and yield of lettuce (Lactuca sativa L. ‘Subyana F1’) grown in a hydroponic system. During the experiments the following conditions were maintained: photoperiod 12h; temperature 22°C; relative humidity (RH) 65–70%. LED lamps emitted the following light colours: white, blue and white+blue (50:50) (described as W, B and W+B). For all colours, quantum irradiance was 70μmolm−2s−1. Plants were fertigated with a standard nutrient solution with the following chemical composition (mgdm−3): N-NH4<10, N-NO3 150, P-PO4 50, K 150, Ca 150, Mg 50, Fe 3.00, Mn 0.5, Zn 0.44, Cu 0.03, B 0.01; pH 5.50, EC 1.8mScm−1. The analysed factors significantly modified photosynthetic activity, growth, yield, chlorophyll content (SPAD measurements) and chemical composition of plants. The highest net photosynthesis rate (PN) was recorded in plants cultivated with O3-I under W+B light, while the lowest was observed for O3-II under B light. In the case of O3-II a highly significant increase of mean N content in leaves was observed, together with decreases of P, Ca, Mg, Na, Fe and Mn contents in comparison to control plants. An improvement of yield (although not statistically significant) was found in O3-I plants, while O3-II application caused a decrease of the yield, for B light by about −27.87%, for W −53.74% and for W+B −46.51%. Similar observations were noted for the number of leaves. Moreover, a significant effect of O3-I on chlorophyll content was noted, excluding plants cultivated under W light. It seems that ozonization of seeds improves their germination and some other growth and physiological processes, while a second ozonization impairs the condition of plants and has a similar effect as tropospheric ozone in outside conditions. From the practical point of view, it would be interesting to investigate the effect of ozonization and other light colours on different crop species.

Nutritional responses of Cordyline fruticosa var. ‘Red Edge’ to fertigation with leachates vs. conventional fertigation: Sodium, potassium, calcium and magnesium

The sequential reuse of drainage water in greenhouse horticulture production to grow successively more salt tolerant crops is proposed as a sustainable alternative to recirculation systems when the irrigation water quality is low. This practice is known as Serial Biological Concentration or Integrated Farm Drainage Management. The objective of this assay was to assess the nutritional responses of Cordyline fruticosa var. ‘Red Edge’ (a semi-tolerant crop) fertigated with leachates from Citrullus lanatus (horticultural crop) cultivated on rockwool, compared to a conventional fertigation. Four treatments were tested: T1 (nutritionally balanced control or standard nutrient solution, with an electrical conductivity (EC) of 2.5dSm−1); T2 (saline control; T2 diluted to an EC of 1.5dSm−1, afterwards, NaCl was added to achieve 2.5dSm−1);T3 (pure leachate from the hydroponic culture of C. lanatus), and T4 (diluted leachates, T3 diluted with irrigation water to 2.5dSm−1). At the end of the trial, biometric parameters were determined and Na+, K+, Ca2+ and Mg2+ concentrations and the accumulation in photosynthetic organs (leaves), conductive organs (stems and petioles) and absorption organs (roots) were measured. The treatments tested had no effect on the number of leaves, leaf area per plant, leaf size, plant fresh and dry weight and shoot:root dry weight ratio. Nevertheless, the plants fertigated with pure leachates were significantly smaller. Regarding the plants’ fresh:dry weight ratio, this was significantly lower when plants were fertigated with pure leachates than with diluted leachates. The use of pure leachates does not cause an increment in total Na+ accumulation with respect to the nutritionally balanced control because Na+ concentration increases only in stems and petioles. Total K+ accumulation decreased when plants were irrigated with solutions with high concentrations of NaCl. The high Ca2+ concentration in the non-diluted leachate led to a high total Ca2+ accumulation. Total Mg2+ accumulation was affected negatively by Ca2+ uptake. It can be concluded that diluted leachates from C. lanatus can be used for the fertigation of C. fruticosa.

Growth performances and changes of macronutrient ion concentrations in the culture medium when Euglena gracilis was cultured with nitrified digestate

ABSTRACTWe investigated the possibility of using Euglena gracilis to convert digestate from methane fermentation of organic wastes into a medium for soilless crop culture. The growth of E. gracilis cultured with aqueous solutions containing filtrate of raw digestate at 1–30% (v/v) and nitrified digestate at 10–100% (v/v) was examined. Concentrations of plant macronutrient ions in nitrified digestate before and after culturing E. gracilis were also examined. Specific growth rates in aqueous solutions containing filtrate of raw digestate at 1–10% and nitrified digestate at 10–100% showed no significant differences, respectively (0.781 ± 0.031 d−1 and 0.925 ± 0.033 d−1, mean ± standard error). The rates in the filtrate of nitrified digestate were significantly higher than those in the filtrate of raw digestate. Moreover, there were no significant differences between the concentrations of plant macronutrient ions other than in the filtrate of nitrified digestate before and after culturing E. gracilis. The concentration of decreased significantly by 10.5% of the initial concentration. As a result, the constituent ratio of plant macronutrient ions other than magnesium in the solution after culturing E. gracilis was similar to that in a standard nutrient solution for soilless culture.

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This research was conducted to establish the relationship between population density to total dry biomass production and estimate the nutrient absorption curve in a hydroponics system for Rosmarinus officinalis L. Study was carried out at the Center for Research and Development of Hydroponics in Faculty of Agronomy at the Autonomous University of Nuevo Leon. Three population densities viz., 8, 16 and 24 plants per square meter were evaluated in a hydroponic system, using volcanic rock with grain diameter of 20-40 mm as an inert substrate and a standard hydroponic nutrient solution. Among tested three plant densities, population density of 8 plants m -2 , total dry biomass production produced highest, total dry biomass and it shows superiority over the plant density with 16 to 24 plants m -2 populations. There were no significant differences in plant height. The data obtained were fitted to linear growth models, which were used to estimate nutrient absorption curves.

USING OF AGRICULTURAL DRAINAGE WATER FOR LETTUCE PRODUCTION IN HYDROPONIC SYSTEM

The objectives of the present work were to study the effects of irrigation with Agricultural Drainage Water (ADW) on lettuce (Lactuca sativa L.) yield, quality, and water use efficiency (WUE) with hydroponic system. Five mixing treatments of Agricultural drainage water (ADW) with fresh water (mean normal irrigation water) were used T1:(100% agricultural drainage water), T2:(75% agricultural drainage water mixed with 25% fresh water), T3:(50% agricultural drainage water mixed with 50% fresh water), T4:(25% agricultural drainage water mixed with 75% fresh water), and T5:( 100% fresh water). Nutrient Film Technique (NFT) hydroponic system was developed with five pipes PVC and nutrient solution added in rates: 12.5%, 25%, 50%, 75%, and 100% from standard nutrient solution for T1, T2, T3, T4, and T5, respectively. The results showed that lettuce plant can be produced in 50 days from planting to harvest by (NFT) hydroponic system. Moreover irrigation by using T3 had effectively increased the yields of green and dry matter. The higher Lettuce yields obtained with trend T3 > T5 > T2 > T4 > T1. And plants irrigated with T3 used water more efficiently than those irrigated with other water treatments. The higher water use efficiency (WUE) 39.96 kg/m3 was obtained with T3 and the lower value 16.67 with T1. On the other hand mineral nutrient contents in dry matter of N, P, K, and Ca contents were obviously higher in plants irrigated with T5 than with other water treatments. Heavy metals (Cd, Ni, Cr and Pb) contents in Lettuce shoots were higher in plants irrigated with T3 than those irrigated with other water treatments, but their levels did not reached the maximum allowed levels by FAO for edible crops.

Recycling of biodiesel fuel wastewater for use as a liquid fertilizer for hydroponics

Wastewater is discharged during washing processes in the production of biodiesel fuel (BDF) using alkaline catalysts. It can be recycled as a liquid fertilizer for hydroponics by adding essential components for plant growth. The effects of the liquid fertilizer on plant growth were investigated. Liquid fertilizer containing a smaller amount of the BDF wastewater had a similar effect on plant growth as the standard nutrient solutions. This result reveals that BDF wastewater can be recycled for use as a liquid fertilizer for hydroponics. However, fertilizer with a larger amount of the BDF wastewater showed poor and varied plant growth due to the growth of microorganisms in the contaminated wastewater. Hence, when BDF wastewater becomes contaminated during storage, sterilization is necessary to recycle it as a liquid fertilizer. Moreover, contamination during storage should be avoided for successful recycling.

Growing Different Lactuca Genotypes Aeroponically within a Tropical Greenhouse—Cool Rootzone Temperatures Decreased Rootzone Ethylene Concentrations and Increased Shoot Growth

Temperate crops cannot grow well in the tropics without rootzone cooling. As cooling increased production costs, this experiment aimed to study the growth of various Lactuca genotypes and propose possible ways of reducing these costs, without compromising productivity. A recombinant inbred line (RIL) of lettuce and its parental lines (L. serriola and L. sativa “Salinas”) were grown aeroponically in a tropical greenhouse under 24°C cool (C) or warm fluctuating 30–36°C ambient (A) rootzone temperature (RZT). Their roots were misted with Netherlands standard nutrient solution for 1 min, at intervals of either 5 min (A5, C5) or 10 min (A10, C10) in attempting to reduce electricity consumption and production costs. Lower mortality and higher productivity were observed in all genotypes when grown in C-RZT. Higher shoot fresh weight was observed under C5 than C10, for the RIL and L. serriola. Since “Salinas” had similar shoot fresh weight at both C-RZ treatments, this may indicate it is more sensitive to RZT than water availability. Under A-RZ treatments, higher carotenoid content, with correspondingly higher nonphotochemical quenching, was observed in A10 for the RIL and “Salinas.” Further, total chlorophyll content was also highest at this RZ treatment for the RIL though photochemical quenching was contrastingly the lowest. Cumulatively, productivity was compromised at A10 as the RIL seemed to prioritize photoprotection over efficiency in photosynthesis, under conditions of higher RZT and lower water availability. Generally, higher RZ ethylene concentrations accumulated in A10 and C10 than A5 and C5, respectively—probably due to spray frequency exerting a greater effect on RZ ethylene accumulation than RZT. In the C5 RZ treatment, lowest RZ ethylene concentration corresponded with highest shoot fresh weight. As such, further research on ethylene (in)sensitivity and water use efficiency could be conducted to identify Lactuca cultivars that are better suited for growth in the tropics, so as to allay production costs with reduced cooling and spray intervals.