In order to simulate the usage of brackish irrigation water in greenhouse tomato (Lycopersicum esculentum Mill. cv. Daniela) culture in perlite, plants were supplied with nutrient solutions containing 0, 20, 40, and 60 mm NaCl. The three highest salinity treatments were applied at three different plant growth stages, during early vegetative growth [16 days after transplanting, (DAT)], beginning of flowering (36 DAT), and starting fruit development (66 DAT). Salt tolerance of tomato plants increased when the application of salinity was delayed. Salinity significantly decreased size and number of marketable fruits, but increased fruit quality by increasing total soluble solids and sugar content. Leaf and fruit calcium and potassium concentrations were decreased significantly by increasing salinity levels. This was compensated for the accumulation of sodium. Anion accumulation was increased by increasing chloride concentration. These results indicate that it is feasible to use brackish water for growing tomato with minimum yield losses if salt concentration and duration of exposure are carefully monitored.
In a completely closed hydroponic system, Na and Cl commonly accumulate in the root zone, at rates depending on the concentration of NaCl in the irrigation water (rate of Na and Cl inlet) and the Na to water and Cl to water ratios at which they are taken up by the plants (rates of Na and Cl outlet). However, while the concentration of NaCl in the irrigation water is commonly a constant, the Na to water and Cl to water uptake ratios are variables depending on the concentrations of Na and Cl in the root zone and, hence, on the rates of their accumulation. To quantify this feed-back relationship, a differential equation was established, relating the rate of Na (or Cl) accumulation to the rate of water uptake. This equation was solved according to the classical Runge-Kutta numerical method using data originating from a cucumber experiment, which was conducted in a fully automated, closed-loop hydroponic installation. Four different NaCl concentrations in the irrigation water, 0.8, 5, 10 and 15 mm, were applied as experimental treatments. The theoretically calculated curves followed a convex pattern, with an initially rapid increase of the Na and Cl concentrations in the root zone and a gradual leveling out as the cumulative water consumption was rising. This was ascribed to the gradual approaching of the Na to water and Cl to water outlet ratios via plant uptake, which were increasing as NaCl was accumulating in the root zone, to the constant NaCl to water inlet ratio (NaCl concentration in irrigation water). The model could predict the measured Na and Cl concentrations in the drainage water more accurately at 10 and 15 mm NaCl than at 0.8 and 5 mm NaCl in the irrigation water. Possible explanations for these differences are discussed. Plant growth and water uptake were restricted as salinity was increasing, following a reverse pattern to that of Na and Cl accumulation in the root zone. The leaf K, Mg and P concentrations were markedly restricted by the increasing salinity, while that of Ca was less severely affected.
The present study was conducted to determine the critical optimum and toxic concentrations of potassium (K) using segmented analysis and its relationship with some physiological, anatomical, and nutritional responses to increasing K in hydroponically grown Lilium sp. L. cv. Arcachon. Plants were fertigated with nutrient solutions containing K (Kext) at 0, 2.5, 5.0, 7.5, 12.5, 17.5, 22.5, and 30 mmol·L−1. Maximum flower diameter occurred when, on a dry mass basis, shoot K (Kint) ranged from 504 to 892 mmol·kg−1; however, a lower Kint was required to obtain maximum biomass accumulation and shoot length (384 and 303 mmol·kg−1, respectively). Potassium increased in all plant organs as K in the nutrient solution increased. Nitrogen increased in young leaves and magnesium (Mg) decreased as Kext increased. Concentrations of Kext from 5 to 17.5 mmol·L−1 increased the size of chlorenchyma and occlusive cells; however, metaxylem vessels were unaffected. Net photosynthetic rate was higher in young leaves, whereas water potential increased in both young and mature leaves when Kext was greater than 22.5 mmol·L−1. Critical concentrations varied according to the growth parameter. Optimum Kint ranged from 303 to 384 mmol·kg−1 for vegetative parts, whereas parameters related with flower growth ranged from 427 to 504 mmol·kg−1. Concentration of 504 mmol·kg−1 Kint was associated with optimum growth for all the parameters assessed, whereas a Kint greater than 864 mmol·kg−1 was associated with a decline in growth; thus, these concentrations were considered as the critical optimum and critical toxicity levels, respectively. The optimum and toxicity critical Kint were estimated when Kext in the nutrient solutions was 5.6 and 13.6 mmol·L−1, respectively.
Strawberry (`Chandler') plants were grown in a greenhouse hydroponic culture system from 28 Apr. to 20 July to produce runners (stolons) with several daughter plants. By mid-July, each `Chandler' plant had developed about 30 daughter plants on 12 runners with 1 to 6 daughter plants on each runner. Daughter plants varied in weight from <0.9 to >10 g. Daughter plant weight and position on the runner affected new root development on plug plants during the first 7 days under mist irrigation. At 3 weeks, 87% of daughter plants that weighed <0.9 g and at least 96% of daughter plants that weighed >1.0 g were rated acceptable for field transplanting, respectively. The percentage of daughter plants from second to tenth node position that were rated acceptable for field planting ranged from 98% to 88%, respectively. Runner production in the fall was not affected by either position on the runner or weight at the time of daughter plant harvest. But, larger daughter plants produced more branch crowns than did smaller daughter plants in the fall. Transplant survival in the field was 100%. In the spring, `Chandler' plants produced a 10% greater yield from daughter plants that weighed 9.9 g compared to those that weighed only 0.9 g.
The objective of this study was to discriminate among Na, Cl, and Ca salinity effects on cucumber (Cucumis sativus L.). Cucumber plants grown in perlite were exposed for 134 days to low and moderate levels of salinity induced by the addition of either NaCl or CaCl2 at equal rates (on a chemical equivalent basis) to a standard nutrient solution for cucumber up to two target electrical conductivity (EC) levels (3.0 and 5.0 dS·m–1). The experimental treatments included also a control, which was irrigated with the standard nutrient solution without additional salt. The mean EC values in the drainage solution were 2.35, 3.94, 4.2, 6.31, and 6.35 dS·m–1 for the control, low NaCl, low CaCl2, high NaCl, and high CaCl2 treatments, respectively. The fresh and dry weights of stems and leaves were reduced only under conditions of high NaCl salinity, whereas root mass was not affected. Fruit yield decreased in proportion to the increase in NaCl salinity, while CaCl2 salinity reduced yield only at the high EC, to a level that corresponded to the low NaCl salinity. The suppression of yield with increasing salinity resulted mainly from a decrease in fruit size, while the number of fruit per plant was reduced to a lesser extent. These changes caused a reduction in the number of Class I fruit and an increase in nonmarketable produce. Both salinity sources enhanced the total soluble solids and the fruit chlorophyll concentration. NaCl salinity appreciably raised the concentrations of Na and Cl in young and old leaves, and suppressed the K concentration. CaCl2 salinity increased leaf Cl and Ca levels and diminished Mg and K. It is concluded that cucumber is more susceptible to NaCl salinity than to equal EC levels of CaCl2 salinity.
The evolution of plastic uses (excluding glazing) in the production of greenhouse vegetables is presented. Plastics are used in almost every aspect of crop production, including providing a barrier to the soil, lining crop production troughs, holding soil and soilless media, and providing a nutrient film channel. Irrigation systems have become very elaborate, with various plastic products used to transport water and nutrients and to provide a means of emitting nutrient solution to the crop. The greenhouse environment is managed from several plastic components, including air distribution tubes, shade materials, and energy curtains. Plastics are now common in greenhouse vegetable crop training, insect monitoring, postharvest handling, storage, and marketing.
A 2-year study (2012–13 and 2013–14) was conducted to evaluate the effect of plant growth regulator’s (PGRs) on plant growth, yield, and quality of hydroponically grown sweet peppers. In 2012–13, sweet pepper plants were subjected to two levels of gibberellic acid (GA3) (10 and 15 mg·L−1), two levels of naphthalene acetic acid (NAA) (15 and 30 mg·L−1), and four combinations of NAA and GA3 (10 mg·L−1 GA3 + 15 mg·L−1 NAA, 10 mg·L−1 GA3 + 30 mg·L−1 NAA, 15 mg·L−1 GA3 + 15 mg·L−1 NAA, and 15 mg·L−1 GA3 + 30 mg·L−1 NAA) applied to plants at flower initiation in a non-temperature-controlled tunnel. This PGR application was repeated 60 days after transplanting (DAT). In 2013–14, in addition to previously mentioned treatments, two levels of 4-chlorophenoxyacetic acid (4-CPA), at 30 and 45 mg·L−1, were applied at flower initiation followed by three additional applications of the latter treatments at 20-day intervals in a temperature-controlled tunnel. Marketable and total yield were markedly reduced by application of 4-CPA at 30 and 45 mg·L−1. Plant height was increased by application of GA3, and GA3 in combination with NAA, compared with application of 4-CPA, 30 mg·L−1 NAA, and the control. Results also showed that application of GA3 at 10 and 15 mg·L−1 or in combination with NAA increased plant fresh and dry mass as well; however, this had no beneficial effect on the yield of sweet pepper fruit. The application methods and concentrations of various PGRs needs further investigation under different growing conditions on sweet pepper cultivars.
Mini or “baby” vegetables have become increasingly popular items for restaurant chefs and retail sales. Squash (Cucurbita pepo) are generally open-field cultivated where climate, insect, and disease pressures create challenging conditions for growers and shippers who produce and market this delicate, immature fruit. In order to overcome these challenges, in Spring 2003 and 2004, 18 squash cultivars, including zucchini, yellow-summer, patty pan/scallop, and cousa types, were grown hydroponically in a passively ventilated greenhouse and compared for yield of “baby”-size fruit. Squash were graded as “baby” when they were less than 4 inches in length for zucchini, yellow-summer, and cousa types and less than 1.5 inches diameter for round and patty pan/scallop types. In both seasons, `Sunburst' (patty pan) produced the greatest number of baby-size fruit per plant, while `Bareket' (green zucchini) produced the least. The zucchini-types produced between 16 and 25 baby-size fruit per plant in 2003. The yellow summer squash-types produced on average 45 baby fruit per plant. The production of the patty pan/scallop types ranged from 50 to 67 baby-size fruit per plant depending on cultivar. The cousa types produced approximately 30 baby-size fruit. Total yields were lower in 2004 due to a shortened season. Squash plants will produce numerous high quality baby-sized fruit when grown hydroponically in a reduced pesticide environment of a greenhouse where they can be harvested, packaged, and distributed to buyers daily. The cultivars Hurricane, Raven, Gold Rush, Goldy, Sunray, Seneca Supreme, Supersett, Butter Scallop, Sunburst, Patty Green Tint, Starship, Magda, and HA-187 could be used for hydroponic baby squash production.
Hydroponic systems have become increasingly popular for growers in recent years for year-round local production. Whereas optimal air temperature for plant growth has been considered, optimal root zone temperatures have not been examined as thoroughly. The objective of this research was to determine the optimal water temperature for growing different types of basil hydroponically. Research was conducted at the greenhouses in Stillwater, OK. Seventeen cultivars were selected from six main types of basil and transplanted into Nutrient Film Technique hydroponic systems, and three water temperature treatments were applied: 23, 27.5, and 31 °C. Height, width, average leaf area, leaf number, chlorophyll concentration (chlorophyll readings obtained with the Minolta-502 SPAD meter), shoot fresh weight, shoot dry weight, and root dry weight were evaluated. In general, the 27.5 and 31 °C treatments were not greater than each other in terms of leaf number and root dry weight but were greater than the 23 °C treatment. The 31 °C treatment had the greatest height, whereas width, average leaf area, shoot fresh weight, and shoot dry weight were not different from the 27.5 °C treatment. The 23 °C treatment had the greatest chlorophyll concentration (SPAD) value. Cultivar differences were significant in average leaf area and SPAD, with ‘Spicy Bush’ having the smallest leaf area and purple basil having the greatest SPAD value. For all cultivars except purple basil and ‘Large Leaf Italian’, a 27.5 °C water temperature would be recommended for greater plant growth.
Plants can synthesize some antioxidants, including L-ascorbic acid (AsA) and polyphenol, in response to environmental stresses. Antioxidants detoxify reactive oxygen species in plants and also aid in human health. In this study, we demonstrate that a novel hydroponic treatment can increase leafy vegetable nutritional quality without retarding growth. Leaf lettuce (Lactuca sativa) was grown hydroponically and subjected to rhizosphere drought stress by lowering the water level in the solution tub before harvesting. Appropriate drought stress using this method could increase AsA, polyphenol, and sugar content by 24%, 50%, and 17%, respectively, and decrease nitrate nitrogen content by 18% without reducing yield. Similar effects of drought stress on AsA content were observed in four other plant species. This hydroponic method has a universal potential to increase leafy vegetable quality without reducing yield in controlled environments such as plant factories.