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 -.
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).
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.
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.
Growth and photosynthetic parameters were measured in Eustoma grandiflorum (Raf.) Shinn. ‘Umihonoka’ grown hydroponically under nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), or magnesium (Mg) deficiency in 1/2 strength of modified Johnson’s solution. Plant height, node number, and leaf area were all reduced under N, P, K, and Ca deficiencies but not under Mg deficiency as compared with plants grown in the complete nutrient solution. Shoot and root dry weight were reduced in the N-, P-, K-, and Ca-deficient treatments, whereas root but not shoot dry weight was lowered by Mg-deficient treatment. Shoot-to-root dry weight ratio decreased under N and P deficiencies, increased under K and Mg deficiency, but was not altered under Ca deficiency. Decreased net photosynthetic rate (Pn) of N-, P-, and K-deficient leaves was all related to lower stomatal conductance (g S), whereas N-deficient leaves also accompanied by a higher intercellular carbon dioxide concentration (Ci). The Mg-deficient treatment did not alter chlorophyll fluorescence Fv/Fm, maximal fluorescence (Fm), or minimal fluorescence (Fo). Decreased Fv/Fm of N-, P-, K-, and Ca-deficient leaves was all related to lower Fm, whereas N- and P-deficient leaves also accompanied by lower Fo. A key was developed for the identification of N, P, K, Ca, and Mg deficiency symptoms.
Greenhouse experiments were conducted in 2005 and 2006 near Live Oak, FL, to develop fertilization programs for fresh-cut ‘Nufar’ basil (Ocimum basilicum) and spearmint (Mentha spicata) in troughs with soilless media using inputs compliant with the U.S. Department of Agriculture's National Organic Program (NOP). Four NOP-compliant fertilizer treatments were evaluated in comparison with a conventional control. Treatments and their analyses in nitrogen (N), phosphorus (P), and potassium (K) contents are as follows: conventional hydroponic nutrient solution [HNS (150 ppm N, 50 ppm P, and 200 ppm K)], granular poultry (GP) litter (4N–0.9P–2.5K), granular composite [GC (4N–0.9P–3.3K)], granular meal [GM (8N–2.2P–4.1K)], and GM plus a sidedress application of 5N–0.9P–1.7K fish emulsion (GM + FE). Electrical conductivity (EC) of the media, fresh petiole sap nitrate (NO3-N) and K concentrations, dried whole leaf NO3-N, P, and K concentrations, and yield and postharvest quality of harvested herbs were evaluated in response to the treatments. Basil yield was similar with HNS (340 g/plant) and GP (325 g/plant) in 2005 and greatest with HNS (417 g/plant) in 2006. Spearmint yield was similar with all treatments in 2005. In 2006, spearmint yields were similar with the HNS and GP yields (172 and 189 g/plant, respectively) and greater than the yields with the remaining treatments. In both years and crops, media EC values were generally greater with the GC than with the GP, GM, and GM + FE treatments but not in all cases and ranged from 1.77 to 0.55 dS·m−1 during the experiments. Furthermore, HNS media EC values were consistently equal to or lower than the GP media EC values except with EC measurements on 106 days after transplanting in both crops in 2005. Petiole NO3-N and K results were variable among crops and years, but provided valuable insight into the EC and yield data. We expected EC, petiole NO3-N, and petiole K to be consistently higher with HNS than with organic treatments, but they were not, indicating a reasonable synchrony of nutrient availability and crop demand among the organic treatments. The postharvest quality of both basil and spearmint was excellent with all treatments with few exceptions.
Rockwool is an excellent growing medium for the hydroponic production of tomato; however, the standard size rockwool blocks [4 × 4 × 2.5 inches (10 × 10 × 6.3 cm) or 3 × 3 × 2.5 inches (7.5 × 7.5 × 6.3 cm)] are expensive. The following experiments were conducted with less expensive minirock wool blocks (MRBs), on rayon polyester material (RPM) as a bench top liner, to reduce the production cost of tomatoes (Lycopersicon esculentum) grown in a limited-cluster, ebb and flood hydroponic cultivation system. Fruit yield for single-cluster plants growing in MRBs [2 × 2 × 1.6 inches (5 × 5 × 4 cm) and 1.6 × 1.6 × 1.6 inches (4 × 4 × 4 cm)] was not significantly different from plants grown in larger sized blocks (3 × 3 × 2.5 inches). When the bench top was lined with RPM, roots penetrated the RPM, and an extensive root mat developed between the RPM and the bench top. The fruit yield from plants on RPM was significantly increased compared to plants without RPM due to increases in fruit size and fruit number. RPM also significantly reduced the incidence of blossom-end rot. In a second experiment, single- and double-cluster plants were grown on RPM. Fruit yield for double-cluster plants was 40% greater than for single-cluster plants due to an increase in fruit number, although the fruit were smaller in size. As in the first experiment, fruit yield for all plants grown in MRBs was not significantly different from plants grown in the larger sized blocks. MRBs and a RPM bench liner are an effective combination in the production of limited-cluster hydroponic tomatoes.
Cucumbers (Cucumis sativus L. `Vetomil') were grown in rockwool or perlite to evaluate these media for efficient hydroponic cucumber production under Florida greenhouse conditions. Plants were grown using a double-stem training method, and the frequency of irrigations was controlled by a weighing lysimeter for each treatment. In Expt. 1, plants were grown in rockwool with 29% or 17% leaching fraction (LF) and in perlite with a 17% LF. Nitrogen, P, and K concentrations in the complete nutrient solution were 175, 50, and 180 mg·L−1, respectively. In Expt. 2, N, P, and K concentrations were increased to 225, 60, and 225 mg·L−1, respectively. Other nutrient concentrations and LFs remained as in Expt. 1. In Expt. 1, yields (fruit count and total fruit mass) were higher from plants grown in rockwool at 29% LF than from plants grown in rockwool or perlite at 17% LF. However, in Expt. 2, when nutrient concentrations were higher, total fruit mass was greater from plants grown at the lower LF, although there was no difference in fruit number. In both experiments, cucumber yield did not differ when grown at the same LF in either rockwool or perlite. Electrical conductivity (EC) and pH of the nutrient solution from the growing bags were not affected when LFs were decreased. In Expt. 1, the pH and EC ranged from 6.1 to 7.0 and from 0.9 to 1.6 mS·cm−1, respectively, across all treatments. In Expt. 2, pH and EC ranged from 5.3 to 6.9 and from 0.6 to 2.5 mS·cm−1, respectively, across all treatments.
Four experiments were conducted from 1992 to 1994 to determine the concentrations of N and P required to maximize yields of rockwool-grown cucumbers (Cucumis sativus `Vetomil') trained with a double-stem method. Concentrations of N and P in rockwool slabs were monitored throughout growth of greenhouse-grown cucumbers. The onset and duration of nutrient depletion in the slabs were related to cucumber yield. In Expt. 1, treatment-1 plants received a two-step solution containing N at 90 and 175 mg·L−1 during successive growth phases, while treatment-2 and -3 plants were grown with N at a constant 175 or 225 mg·L−1. Phosphorus was provided at 50 mg·L−1 in all treatments. Treatment 1 was excluded from Expt. 2. In Expts. 3 and 4, plants were grown with N at 225 or 275 mg·L−1 and P at 75 mg·L−1. Onset of N and P depletion (to <10 mg·L−1) in the growing slabs occurred during the early fruiting stage of cucumber, 1 to 8 days before first harvest. The duration of N and P depletion decreased, and cucumber yields increased with increasing N and P concentrations. When plants were grown with N and P at 275 and 75 mg·L1, respectively, N was depleted in the growing slabs during only one experiment and then for only 4 days, and slab P concentration remained >10 mg·L1. Therefore, under Florida conditions, when growing cucumbers in rockwool using a double-stem training technique, N and P should be provided at 275 and 75 mg·L−1, respectively, to minimize depletion of these nutrients from the growing medium.
Bahiagrass (Paspalum notatum) is widely used for slope protection and water and soil conservation in southern China. The plants develop an extensive root system that plays a crucial role in the protection of both soil and water. However, little is currently known about the factors that influence early root growth in bahiagrass. Here, the effects of boron (B), calcium (Ca), iron (Fe), lanthanum (La), cerium (Ce), salicylic acid (SA), and melatonin (MLT) on root growth characteristics were examined. Bahiagrass seedlings were grown in 1/25 strength modified Hoagland nutrient solution supplemented with boric acid, calcium chloride, ferric ethylenediaminetetraacetic acid (Fe-EDTA), lanthanum chloride, cerium chloride, SA, or MLT. Root lengths, root surface areas, and the number of root tips were analyzed using a root scanning system after 2, 4, and 6 days of treatment. We found significant effects on root growth after some treatments. Thus, 0.270 or 0.360 mm B for 2 days enhanced root tip number, whereas 0.15 mm Fe for 6 days increased root surface area. Although 3 or 5 mm Ca caused an increase in root tip numbers, the root length was reduced. The addition of La to the nutrient solution significantly increased root length and surface area, and addition of Ce increased root surface area and root tip numbers. Root growth characteristics were optimal after 0.3 μm La for 6 days or 1.0 μm La for 4 days. For Ce treatment, optimal root characteristics were observed at 0.5 μm Ce for 6 days. Root tip numbers increased after 0.1 or 1.0 μm MLT for 6 days, whereas SA treatment reduced the root length, surface area, and root tip numbers. Overall, the analyses indicate that treatment with B, Fe, La, Ce, and MLT benefited root growth in bahiagrass seedlings.