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N.C. Yorio, G.W. Stutte, D.S. DeVilliers, R.M. Wheeler, and R.L. Langhans

Bean (Phaseolus vulgaris L.) cv. Etna, a dry bean variety, and cv. Hystyle, a snap bean variety, were grown at 400 and 1200 μmol·m-2·s-1 CO2 to determine the effects of CO2 enrichment on plant growth and stomatal conductance. Plants were grown in controlled environment chambers for 70 days at each CO2 level using nutrient film technique hydroponics. An 18-h light/6-h dark photoperiod was maintained for each test, with a corresponding thermoperiod of 28 °C/24 °C and constant 65% RH. Diurnal stomatal conductance measurements were made with a steady-state porometer at 28 days after planting (DAP) and 49 DAP. As expected, plant growth and yield was consistently increased for each cultivar when plants were grown at 1200 μmol·m-2·s-1 CO2 compared to 400 μmol·m-2·s-1 CO2. Stomatal conductance measured during the light period showed an expected decrease for each cultivar when grown at 1200 μmol·m-2·s-1 CO2 compared to 400 μmol·m-2·s-1 CO2. However, during the dark period, stomatal conductance was higher for each cultivar grown at 1200 μmol·m-2·s-1 CO2. These results suggest a stomatal opening effect in the dark when plants are exposed to enriched levels of CO2. Tests are underway to investigate the effects of CO2 levels greater than 1200 μmol·m-2·s-1 on the growth and stomatal conductance of bean.

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H. Zekki, L. Gauthier, and A. Gosselin

Tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in the three most promising and used hydroponic cultivation systems using rockwool and peatmoss substrates and nutrient film technique (NFT), either with or without recovery and recycling of the drainage solutions. Prolonged recycling of nutrient solutions in NFT caused a reduction in fresh weight, dry weight, and yield compared to plants grown in NFT with regular renewal of the nutrient solution. There were no differences in growth, productivity, and leaf mineral composition between plants grown in rockwool and peatmoss systems, with or without recycling, and in the NFT system without recycling. These results suggest that recycling drainage solutions is an economically and environmentally sound horticultural practice that when used correctly does not cause a reduction in yield of tomatoes cultivated in rockwool or peatmoss. However, prolonged use of the same solution in the NFT cultivation system can negatively affect growth and yield. This is most likely due to an accumulation of sulfate ions in the fertigation solutions.

Open access

Hardeep Singh, Bruce Dunn, Mark Payton, and Lynn Brandenberger

Nutrient-film technique (NFT) trials were conducted to quantify the effect of two different water-soluble hydroponic fertilizers (5N–4.8P–21.6K and 5N–5.2P–21.6K) on different cultivars of lettuce (Lactuca sativa), basil (Ocimum basilicum), and swiss chard (Beta vulgaris). Results indicated swiss chard yield was affected only by cultivars, with Fordhook Giant producing the greatest fresh weight across fertilizer treatments. For lettuce production, interaction between fertilizers and cultivars was significant. ‘Mirlo’ and ‘Rubysky’ had greater growth compared with other cultivars in both fertilizers, whereas Dragoon performed well using 5N–4.8P–21.6K, but not 5N–5.2P–21.6K. For basil, dry weight production showed a significant interaction between fertilizers and cultivars. ‘Largeleaf’ produced greater dry weight with 5N–4.8P–21.6K, whereas ‘Lemon’ produced greater dry weight with 5N–5.2P–21.6K. For nutrient concentration of leaves, the concentrations were within the recommended range for lettuce when fertilized with 5N–5.2P–21.6K. Nutrient concentrations varied by nutrient from the recommended range for basil, but there was no significant difference between fertilizers. For swiss chard, the nutrient concentrations were in the recommended range and there was no difference between fertilizers. Therefore, growers may need to use more than one type of fertilizer for different lettuce and basil cultivars for optimum production, whereas swiss chard cultivars can be selected based on yield regardless of fertilizer.

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Anthony J. D'Angelo and James Quinn

A strategy for controlling pests with biological control was sought for production of salad greens and herbs in a nutrient film technique (NFT) growing system. A case study was initiated in October 1989 using a one half hectare greenhouse range (1988 construction) with no past or present synthetic insecticide use. Problematic pests were aphids and thrips. A natural predator/pest cycle (NPC) area was established (5% of total greenhouse area with potted herbs on benches) to provide an area for predators to establish and reproduce. Introduced predators, which successfully reproduced in the greenhouse, were Apidoletes aphidimyza (aphid control), Amblyseius macKenzie, and A. cucumeris (thrip control), Encarsia formosa (whitefly control), and Phyoseiulus persimilus (two spotted spider mite control), Naturally occuring predators of importance included a wasp parasitoid of aphids (Hymenoptera) and an insect predator, the minute pirate bug (Hemipters, Anthocoridae), which feeds on thrips and aphids.

Two flying predators of aphids (A. aphidimyza and the wasp parasitoid) dispersed well from the NPC area and provided effective control. The technique of applying the thrips predators, a slow moving mite to flats shortly before transplanting provided good dispersal on all transplants. The time for effective control by the predator was 4 to 6 weeks. Effective control was observed in chives but not shorter cycle crops (3 to 5 weeks average). Immature minute pirate bugs were also observed in the chives assisting in control. Effective spider mite control was accomplished 2 to 3 weeks after the release of P. persimills into infested area. Whitefly populations have been effectively controlled by E. formosa.

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N.C. Yorio, C.L. Mackowiak, R.M. Wheeler, and G.W. Stutte

The effects of elevated CO2 on stomatal density and index were investigated for five crop species currently being studied for NASA's Advanced Life Support program. Lettuce (cv. Waldmann's Green) and radish (cv. Giant White Globe) were grown at 400, 1000, 5000, or 10,000 μmol·mol–1 CO2, tomato (cvs. Red Robin and Reimann Philip 75/59) were grown at 400, 1200, 5000, or 10,000 μmol·mol–1 CO2, and wheat (cv. Yecora Rojo) and potato (cv. Denali) were grown at 400, 1000, or 10,000 μmol·mol–1 CO2 within controlled-environment growth chambers using nutrient film technique hydroponics. Leaf impressions were made by applying clear silicone-based RTV coating to the adaxial and abaxial leaf surfaces of three canopy leaves of each crop at each CO2 treatment. Impressions were examined using a light microscope, whereby the number of stomatal complexes and epidermal cells were counted to calculate stomatal density and stomatal index. Results indicate that stomatal density increased for lettuce and radish at 10,000 μmol·mol–1 CO2, whereas tomato density was highest at 1200 μmol·mol–1 CO2. Potato had the lowest density at 1000 μmol·mol–1 CO2, and there was no effect of CO2 on density for wheat. Stomatal index correlated with density for lettuce and tomato; however, stomatal index for radish, potato, and wheat was not influenced by CO2. This suggests that there may be a species-specific CO2 response to epidermal cell size that influences stomatal density and stomatal index.

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Brandon Jewell and Chieri Kubota

Feasible protocols for organic hydroponic production of strawberry are necessary and this study compares the yield and fruit quality of organic and conventional inorganic hydroponic production. Some issues identified with organic hydroponic strawberry production are: 1) dominant ammonium nitrogen form; 2) solution alkalinity; and 3) dissolved oxygen level of nutrient solution. Eighty bare-rooted `Diamante' plantlets were planted in coconut fiber pots with a mixture of coconut coir (30%) and perlite (70%) and grown in a modified nutrient film technique system inside a polycarbonate greenhouse. The organic nutrient solution contains mostly ammonium nitrogen and little nitrate nitrogen. To enhance colonization and activities of nitrifying bacteria, coconut fiber mats were placed in the organic nutrient solution reservoir. A similar system was also introduced for stock solution pre-conditioning where nitrification and pH stabilization were achieved before application to the strawberry plantlets. The organic nutrient solution prior to pre-conditioning had only 1.53 mg·L-1 nitrate nitrogen, although the nitrate nitrogen level increased to 63.2 mg·L-1 after pre-conditioning. The organic nutrient solution pH was 4.5 initially, 8.5 after 24 hours of pre-conditioning, and finally, shifted to and stabilized at 5.7–5.9 after 3 days. Dissolved oxygen level is critical for both nitrifying bacteria activities and plantlet root growth; therefore, oxygen enrichment was achieved by constantly aerating the nutrient solution in the reservoir, which raised the oxygen level from 2.5 to 7.4 mg·L-1. Comparisons of yield and quality of strawberry fruits between organic and inorganic nutrient solutions will be presented and further improvements of hydroponic systems will be discussed.

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Francesco Montesano, Gianfranco Favuzzi, Angelo Parente, Francesco Serio, and Pietro Santamaria

Sustainability of the soilless greenhouse system is under discussion in open cycle systems, where excess nutrient solution (NS) draining from the substrate is released into the environment. Closed growing systems (CGS) lead to the saving of water and fertilizers. The aim of this research was to compare two CGS: nutrient film technique (NFT) and trough-bench technique [Subirrigation (SUB)]. We report the results of yield and water use efficiency (WUE) of tomato (Lycopersicon esculentum Mill. cv. Kabiria) plants. NFT plants were grown with two electrical conductivity (EC) levels (2-4 and 6-8 dS·m-1) of NS (its highest EC was obtained by increasing all the ions therein). In the SUB system, two water tensions (-4 and –8 kPa) of susbtrate were compared; a NS with an electrical conductivity level of 2 dS·m-1 was used. The tensions were measured through tensiometers. Tomato plants were transplanted at the fourth to fifth true-leaf stage into pots containing 8 L of perlite for SUB. In both CGS, the plants were placed on steel gullies (slope of 2%). Six clusters per plant were harvested. Total and commercial yield were not influenced by the CGS (on average, 1959 and 1853 g/plant, respectively). The average weight of the fruit was lower in the SUB system's plants (40 vs. 43 g/fruit, respectively, for SUB and NFT). Salinity and water stresses resulted in a reduction of 26% of the yield and 16% of the average weight of fruits. The WUE was higher in SUB than NFT (30.7 vs. 26.0 g·L-1, respectively). Salinity stress reduced WUE (29.4 v.s 22.6 g·L-1 with 2–4 and 6–8 dS·m-1, respectively), whereas water stress did not.

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Francesco Montesano, Cristina Ferulli, Angelo Parente, Francesco Serio, and Pietro Santamaria

Nutrient solutions (NS) containing moderate to high concentrations of salts are frequently supplied to improve the taste of tomato fruits grown in soilless systems. The aim of this study was to determine whether salinity and water stress affect the tomato fruit quality similarly. The research was conducted in Mola di Bari, Italy, during Autumn 2004, and compared the nutrient film technique (NFT) with the trough-bench technique [Subirrigation (SUB)] in terms of tomato (Lycopersicon esculentum Mill. cv. Kabiria) fruit quality. In the NFT, the plants were grown with two electrical conductivity (EC) levels (2–4 and 6–8 dS·m-1) of NS. The highest EC was obtained by increasing all the ions in the NS. In the SUB system, two water tensions (-4 and -8 kPa) of substrate (perlite) were examinated. At harvest, in each cluster (six/plant), fruit dry matter (DM) and total soluble solids (TSS) were determinated. In the fourth and sixth cluster, vitamin C content and titratable acidity were determined. Total yield was not influenced by either soilless system, while the average weight of the fruit was lower in the SUB. The DM and TTS were influenced by soilless system (on average, 6.6 vs 7.3 g/100 g of fresh matter and 5.3 vs. 5.9 °Brix, with NFT and SUB, respectively). Both of the stresses resulted in the increase of DM and TSS, principally in SUB (water stress) in respect to NFT (salinity stress), while vitamin C and titratable acidity were not influenced by soilless system or water/salinity stress (25.2 mg/100 g fresh matter and 0.45 g/100 mL of citric acid juice, respectively). Results of NFT with the highest EC of NS exceeded 9 dS·m-1, without any stress symptoms in the plants, while EC in the SUB system remained unchanged (about 2.5 dS·m-1).

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Stan C. Hokanson, Fumiomi Takeda, John M. Enns, and Brent L. Black

Tissue-culture derived mother plants were established in a greenhouse suspended-gutter, nutrient-film technique growing system to evaluate runner tip productivity in the system. Effects of cultivar (`Allstar', `Chandler', `Latestar', `Northeaster', and USDA selection B 27) and duration (0, 1, or 2 months) of cold storage at 1 °C on tip viability, rooting success, and performance in fruit production were determined. The average number and weight of runner tips produced in the gutter production system, the capacity of runner tips to form cohesively rooted plug plants, and the number and length of adventitious roots produced by runner tips varied significantly among the cultivars and the three storage durations (0, 1, or 2 months). In the field, plants produced from runner tips stored for 2 months produced more runners than plants produced from freshly harvested runner tips. Crown number differed among the cultivars, but was not affected by cold storage treatment. No treatment differences were noted for the fruit harvest parameters evaluated. The results suggest that the transplants derived from mother plants grown in a greenhouse-based soilless system can be useful for annual plasticulture strawberry production in colder climates. Although long periods of cold storage of runner tips resulted in lower tip-to-transplant conversion ratios, field performance of transplants was not adversely affected. Additional research is needed to improve greenhouse strawberry production practices for increasing runner output and storage conditions that maintain the integrity of cold-stored runner tips. Without these improvements it is unlikely that soilless runner tip production will become a widely accepted technique that would replace the field nursery tip production method currently used by commercial strawberry propagators.

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A.A. Trotman, C.E. Mortley, D.G. Mortley, P.P. David, and P.A. Loretan

Hydroponic growing systems have the potential to maximize phytomass production of peanut (Arachis hypogea) for Controlled Ecological Life Support Systems (CELSS). Two greenhouse experiments were conducted with plant nutrients supplied in a modified Evan's solutionusing a nutrient film technique. The objective of this research was to determine the effect of hydroponic growing systems on pod and foliage yield of `New Improved Spanish' and `Georgia Red' peanut. Sub-objectives were to evaluate (i) the impact of channel size and (ii) the impact of gradation in pore size on the separation of the rooting zone from the zone of gynophore development. The treatments consisted in the first experiment of a wide channel (122 by 15 by 46 cm) fitted with a perforated (3.0mm diam.) PVC grid; a narrow channel (122 by 15 by 15 cm) either fitted with a perforated grid or without a grid. For 'New Improved Spanish' peanut dry foliage yield tended to be higher in the wide channel treatment (0.33 kg/sq m). But the narrow channel yielded the highest mean pod dry weight (0.12 kg/sq m). Pore sizes of the screens ranged from infinity (no screen). perforated grid, square mesh. filtering screen (75u) and solid screen (no pores). For `Georgia Red' peanut, the impact of gradation in pore size of screens was variable: pod number was highest with the filtering (food) screen (216/sq m) but pod dry weight was highest for the square mesh treatment (0.09 kg/sq m). Foliage yield was significantly greater for the filtering (food) screen (1.12 kg/sq m) than in any of the other treatments. The findings of the research indicate that use of screens is feasible and will not retard pod development. The presence of a perforated grid tended to result in lower phytomass production for `New Improved Spanish' peanut.