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Free access

Samuel J. Dunlop, Marta Camps Arbestain, Peter A. Bishop, and Jason J. Wargent

Greenhouse tomato (Lycopersicum esculentum Mill.) producers are urged to reduce their environmental footprint. Here, the suitability of biochar produced from tomato crop green waste as a substrate for soilless, hydroponic tomato production was evaluated. Substrates containing different combinations of biochar (BC) and pine (Pinus radiata D. Don) sawdust (SD) were produced (BC0-SD100, BC25-SD75, BC50-SD50, BC75-SD25, and BC100-SD0) and characterized. The effect of these substrates on tomato growth, yield, and fruit quality was studied. Most of the measured properties of substrates containing biochar were suited to use as a soilless substrate. The electrical conductivity (EC) of substrates containing biochar was initially high (>4.6 mS·cm−1), but was easily reduced to <0.5 mS·cm−1 by rinsing with water before use. The pH of substrates containing biochar was higher than is considered acceptable for tomato production (7.5–9.3) but did not significantly (P < 0.05) affect any plant growth, yield, and fruit quality indicators measured compared with those of plants grown in pine sawdust. The results support the concept of creating a closed loop system whereby biochar produced from tomato crop green waste is used as a substrate for soilless, hydroponic tomato production, providing a sustainable means to support the growth of high-value food crops.

Open access

Athanasios P. Papadopoulos and Herman Tiessen

Abstract

Cultivars of greenhouse tomato (Lycopersicon esculentum Mill.) were grown in the greenhouse and in growth chambers to study the effects of root and air temperature on flowering and yield. A low air temperature of 19° (day)/14°C (night), during the fall crop, caused no reduction in yield when compared with the commonly used 22°/17° air temperature. A 13°/8° air temperature during the spring crop drastically reduced yield compared with the 19°/14°C air temperature. Flowering of ‘Ohio MR-13’ in growth chambers was delayed significantly at air temperatures of 24°/8° compared to 24°/17°, but the flowering of ‘Vendor’ was unaffected by air temperature treatments. Marketable yield of ‘Vendor’ was significantly higher at 24°/8° compared to the 24°/17° treatment, while the marketable yield of ‘Ohio MR-13’ was unaffected. At a constant, day air temperature of 24°, the amount of small fruit decreased as night air temperature was lowered from 17° to 8° and maturity was delayed as night air temperature was lowered from 14° to 8°. The effect of low air temperature on flowering and yield of tomatoes was large and could not be offset by increasing root temperatures. At air temperatures of 24°/17°, 24°/14°, and 24°/8°, marketable yields were affected adversely by the absence of root thermoperiodicity (day to night root temperature variation).

Open access

Athanasios P. Papadopoulos and Herman Tiessen

Abstract

Four cultivars of greenhouse tomato (Lycopersicon esculentum Mill.) were grown in the greenhouse and two cultivars were grown in growth chambers in order to study the effects of root and air temperature on the elemental composition (N, P, K, Ca, and Mg) of leaf tissue. Most of the variation observed in the nutrient composition of leaves was due to air temperature and the cultivar used; only few root temperature effects were significant. Low air temperatures (24°/14°C, 24°/8°, 19°/14°; day/night) resulted in higher N concentrations in the leaf tissue, whereas root temperature had little effect on N. Response to air temperature was similar for P or for N. However, response to high root temperature (27° and 24° in the greenhouse and the growth chamber, respectively) was greater for P than for N. Air and root temperatures had little effect on K concentration in tomato leaves. Consistently high Ca and Mg levels resulted with low air temperatures (24°/8°, 19°/14°, 13°/8°), whereas root temperature had no effect on accumulation of these two nutrients. The incidence of blossom-end-rot in the fruit of all cultivars used in the study was associated with low Ca and Mg levels in the leaf tissue.

Open access

Sharon L. Knight and Cary A. Mitchell

Abstract

Several levels of photosynthetic photon flux density (PPFD) were tested for effects on growth of 4 cultivars of lettuce (Lactuca sativa L.) under controlled-environment conditions. Growth of ‘Salad Bowl’, ‘Bibb’, and ‘Ruby’ was greater at 932 µmol s -1m-2 than at ≤ 644 µmol s-1m-2 under a 16-hour photoperiod. Thirty mM NO3 - or 5 mM NH4 + + 25 mM NO3 - increased leaf dry weight while reducing leaf chlorosis in ‘Salad Bowl’ and ‘Grand Rapids’ relative to that with 15 mM NO3 -, and reduced leaf purpling in ‘Bibb’ and ‘Ruby’ with little or no effect on yield. Continuous illumination with 455 or 918 µmol s-1 m-2 stimulated yield of ‘Salad Bowl’ and ‘Bibb’ when 30 mM N as NH4 + + NO3 - was used relative to that with 15 mM NO3 -.

Open access

Mikal E. Saltveit Jr. and Eric Young

Abstract

A method is described for studying the 3-dimensional distribution of roots grown in a medium consisting of small pieces of glass. After growing to a desired size, the plant is sacrificed by evaporating all water from the media with flowing air. To visualize the undisturbed root system, an immersion oil with the same refractive index as the glass is added to the glass container in which the plant was grown.

Free access

Jonathan M. Frantz, Gregory E. Welbaum, Zhengxing Shen, and Ron Morse

“Float-bed” (FB) is a simple hydroponic system used by the tobacco industry for transplant production. “Ebb-and-flood” (EF) is a modified FB system with periodic draining of the bed to limit water availability and control plant growth. Field-bed cabbage (Brassica oleracea L. gp. Capitata) transplant production was compared with FB, EF, and overhead-irrigated plug-tray greenhouse systems. Plants were produced in May and June and transplanted in a field near Blacksburg, Va., in June and July of 1994 and 1995, respectively. Beds for FB and EF production consisted of galvanized metal troughs (3.3 × 0.8 × 0.3 m) lined with a double layer of 0.075-mm-thick black plastic film. In 1994, both EF and FB seedlings were not hardened before transplanting, were severely stressed after transplanting, and had higher seedling mortality compared with plants from other systems. Plug-tray transplants showed the greatest increase in leaf area following transplanting and matured earlier than seedlings produced in other systems. In 1995, EF- and FB-grown cabbage plants were hardened by withholding water before transplanting, and seedlings had greater fresh mass and leaf area than plug-tray or field-bed seedlings 3.5 weeks after transplanting. Less succulent cabbage transplants were grown in EF and FB systems containing 66 mg·L-1 N (40% by nitrate) and 83 mg·L-1 K. Compared with the FB system, the EF system allowed control of water availability, which slowed plant growth, and increased oxygen concentration in the root zone. Both EF and FB systems are suitable for cabbage transplant production.

Free access

Gregory E. Welbaum, Jonathan M. Frantz, Malkanthi K. Gunatilaka, and Zhengxing Shen

Sweet corn (Zea mays L.) cultivars containing the shrunken-2 (sh2) gene have superior kernel quality but often germinate poorly and display poor seedling vigor. The transplanting of sh2 sweet corn was investigated as a method to improve stand establishment and hasten maturity. Three-week-old plants (sh2 cv. Krispy King) were raised in 200-cell polystyrene trays in either plug-trays (PT), float beds (FB), or ebb-and-flood (EF) production systems and compared with direct-seeded (DS) controls for transplant quality, successful establishment, and early harvest. In 1994, when plants were established in early June, PT plants matured 1 week earlier than DS and FB plants, which had similar mean times to harvest. In 1995, when field planting occurred in July, all plants flowered prematurely when only 60 cm tall. In 1996, the experiment was begun in early May, and survival of all transplants was >85% vs. 54% for DS plants. In 1996, transplants matured 10 to 13 days earlier than DS plants, however, >90% of DS plants produced marketable ears vs. 63%, 49%, and 44% of EF, FB, and PT plants, respectively. The DS plants were also taller with better root development than transplants in all years. Transplants produced smaller, lower-quality ears than did DS plants, thus nullifying the benefits of greater plant populations and earlier maturity. The EF system produced high-quality seedlings because of the greater control of water availability during seedling development. In some areas, the increased value of early sh2 sweet corn may be worth the additional cost of transplanting and greater percentage of unmarketable ears.

Free access

T. Casey Barickman, Dean A. Kopsell, and Carl E. Sams

Plant growth regulators (PGRs) are chemicals used on a wide range of horticultural crops. These exogenous chemicals, similar to endogenous plant hormones, regulate plant development and stimulate a desired growth response, such as control of plant height. One such PGR is abscisic acid (ABA), which has been used effectively to improve fruit quality, specifically sugars and phytonutrients. The purpose of this study was to examine the effects of exogenous applications of ABA on tomato (Solanum lycopersicum) fruit quality, such as carotenoids, soluble sugars and organic acids, and ABA on tomato leaf chlorophylls and carotenoids. Furthermore, this study compared how ABA and calcium (Ca) treatments together affect fruit quality and whether there are added benefits to treating plants with both simultaneously. ABA treatments proved effective in increasing tomato fruit soluble sugars and decreasing organic acid concentrations. This study demonstrated that ABA is a viable PGR to significantly improve tomato fruit quality, specifically pertaining to carotenoids, soluble sugar, and organic acid concentrations.

Free access

Enoc Barrera-Aguilar, Luis A. Valdez-Aguilar, Ana M. Castillo-González, Andrew D. Cartmill, Donita L. Cartmill, Edilberto Avitia-García, and Luis Ibarra-Jímenez

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.

Free access

Youbin Zheng, Linping Wang, and Mike Dixon

Copper (electrolytically generated or from cupric sulfate) is increasingly used to control diseases and algae in the greenhouse industry. However, there is a shortage of information regarding appropriate management strategies for Cu2+ (Cu) in greenhouse hydroponic production. Three greenhouse studies were conducted to examine the growth and yield responses of sweet pepper (Capsicum annuum L., Triple 4, red) to the application of Cu in hydroponic production systems. In the first two experiments, plants were grown on rockwool and irrigated with nutrient solutions containing Cu at concentrations of 0.05, 0.55, 1.05, 1.55, and 2.05 mg·L–1. Copper treatments were started either when plants were 32 days old and continued for 4 weeks, or when plants were 11 weeks old and continued for 18 weeks, respectively. In the third experiment, roots of solution cultured pepper seedlings were exposed to Cu (1.0, 1.5, and 2.0 mg·L–1) containing nutrient solutions for 2 hours per day for 3 weeks. Higher Cu treatment initialized when plants were 32 days old significantly reduced plant leaf number, leaf area, leaf biomass, specific leaf area, stem length and shoot biomass. The calculated Cu toxicity threshold was 0.19 mg·L–1. However, when treatment initialized at plants were 11 weeks old, Cu did not have significant effects on leaf chlorophyll content, leaf area or specific leaf area. Copper started to show significant negative effects on leaf biomass and shoot biomass at 1.05 mg·L–1 or higher levels. Copper treatments did not have any significant effect on fruit number, fresh weight or dry weight. Under all the Cu levels, fresh fruit copper contents were lower than 0.95 mg·kg–1 which is below the drinking water standard of 1.3 mg·kg–1. Seedling growth was significantly reduced by exposing roots to Cu (≥1.0 mg·L–1) containing solutions even for only 2 h·d–1.