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Common ice plant (Mesembryanthemum crystallinum L.) is a novel edible succulent plant with savory flavor. It has epidermal bladder cells (EBCs) that store water and sodium chloride (NaCl) located on the epidermis of the leaves and stems. Ice plant is an obligatory halophyte that requires NaCl for optimum growth. The objective of this study was to determine the impact of NaCl on growth of ice plant for hydroponic production as an edible leafy green and to quantify the ability of ice plant to take up NaCl from the environment. Four-week-old seedlings of ice plant were transplanted into hydroponic systems, established for 1 week, and given five NaCl treatments [0 M (control), 0.05 M, 0.10 M, 0.20 M, 0.40 M NaCl]. Sequential destructive harvests to determine plant growth occurred at day 7, 14, and 21 after NaCl treatment. The 0.05 M NaCl had the greatest stimulating effect on biomass, increasing total fresh weight (FW) by 173% and shoot FW by 193% compared with the control plants. The 0.10 M NaCl also had stimulating effect as compared with 0 M, but plants were not as large as those receiving 0.05 M NaCl. The 0.20 M NaCl had little effect on plant growth compared with the control. The 0.40 M NaCl had a strong stunting effect on plant growth. All plants treated with NaCl had less root weight than the control, and higher NaCl concentration resulted in greater reduction in root weight. However, for the 0.05 and 0.10 M treatment, the gain in shoot weight exceeded the loss in root weight. Plants gained or lost water in a faster rate than dry mass, which resulted in larger differences among treatments in FW than in dry weight (DW). Plants treated with higher NaCl concentrations developed fewer, smaller, and thicker leaves but contained more EBCs per unit leaf surface area. There was high Na and Cl accumulation in leaf tissues of all salt-treated plants (e.g., 180,507 mg·kg⁻¹ Na and 125,084 mg·kg⁻¹ Cl in the 0.05 M treatment vs. 13,558 mg·kg⁻¹ Na and 12,991 mg·kg⁻¹ Cl in the 0 M treatment). This indicated potential for bioremediation of saline soil or hydroponic water. Concentrations of macronutrients such as nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), and sulfur (S) were reduced when plants received increasing NaCl treatments. In general, this study showed that growth of ice plant benefited from 0.05 and 0.10 M NaCl additions to the hydroponic nutrient solution. Ice plant deserves further work on its ability to reduce Na and Cl from accumulating in recirculating hydroponic nutrient solution.

Plant internal nutrient status is known to influence the kinetics of nutrient absorption, but little on this relationship has been reported for roses (Rosa spp. L.). The objectives of this experiment were to determine the influence of NO₃, PO₄, and K deprivation on plant tissue concentrations and relative growth rates and to quantify the influence of nutrient deprivation on absorption kinetic parameters. Rose plants growing in solution culture were deprived of N, P, or K for 0 to 20 days to establish differing tissue concentrations. Absorption kinetics were then determined based on the rate of NO₃, PO₄, or K depletion from solution over a range of concentrations. The data were fit to a modified Michaelis-Menten equation to account for the influence of internal nutrient status on absorption kinetics. Plants deprived of the nutrients for up to 20 d did not show significantly reduced root or plant fresh weight as compared with control plants. Plant tissue concentrations differed significantly by deprivation treatment and varied from 1.4% to 2.3% for N, 0.22% to 0.35% for P, and from 1.0% to 2.0% for K. Plants deprived of NO₃, PO₄, and K subsequently showed increased absorption rates. This was primarily expressed as an increased maximum absorption rate for NO₃ and PO₄. In contrast, K-deprived plants primarily exhibited an increased affinity (decreased K_m) for K. The results demonstrate the plasticity of rose plants to grow and absorb nutrients under varying internal nutrient concentrations. This work quantifies the influence of rose plant nutritional status on the kinetics of NO₃, PO₄, and K absorption. The knowledge would be useful to improve models for providing decision support for fertilization based on plant growth rates and internal nutrient status.

Silicon (Si) is a beneficial nutrient that improves biotic and abiotic stress tolerance of several crop species. Previous Si research with container-grown floriculture crops has either focused on a limited number of species or has been conducted in hydroponics using purified water, but little research has been conducted with plants grown in soilless substrates. The objective of this experiment was to examine whether weekly potassium silicate drenches would alter leaf Si concentration or affect morphological traits of several floriculture species grown in soilless substrate. Rooted liners of 21 cultivars were transplanted into a peat-based substrate. Control plants received no Si supplementation, whereas treated plants were given weekly drenches of 100 mg·L⁻¹ Si from potassium silicate for 10 weeks. Leaf Si concentration of control plants ranged from 211 mg·L⁻¹ for petunia (Petunia ×hybrida Vilm. ‘Cascadias Cherry Spark’) to 2606 mg·L⁻¹ for argyranthemum [Argyranthemum frutescens (L.) Sch. Bip. ‘Sunlight’]. Si supplementation increased leaf Si concentration of 11 cultivars; leaf Si concentrations for these supplemented plants were 13% to 145% greater than control plants. Among the taxa studied, Si supplementation response was variable; Si either increased or decreased height, diameter, fresh weight, dry weight, flower diameter, and leaf thickness. For three cultivars, these morphological traits were apparently unaffected by Si supplementation despite accumulating Si. Similarly, significant morphological differences were observed in four cultivars that did not accumulate Si. Eight cultivars both accumulated Si and showed significant morphological differences. Our results demonstrate that many common floriculture species grown in a peat-based substrate do take up Si and that SI may have an effect on plant development. Consequently, more work is needed to determine the appropriate rate of Si supplementation and to examine additional species.

Fertility management of seedlings and transplants is considered a key challenge in organic greenhouse production. This study was conducted to determine response of greenhouse-grown cucumber (Cucumis sativus) and nutrient release profile to two organic fertilizers and their combinations applied at three different concentrations in organic substrate. The organic fertilizers used were a turkey litter–based compost (TC) and a dairy manure vermicompost (VC). In addition, two control treatments [no fertilization (CK), conventional liquid fertilizer (CF)] were included. For TC, substrate leachate pH decreased for the first 17 days after addition and then increased, whereas electrical conductivity (EC), and calcium (Ca) and nitrate-nitrogen (NO₃ ⁻-N) concentrations increased and then declined. For VC, EC decreased continuously over time from days 0 to 52, whereas pH increased. The Ca and NO₃ ⁻-N concentrations decreased over time to 24 days and then did not change further. For TC/VC combinations, EC was stable for the first 17 days and then declined. For all organic fertilizer applications, potassium concentration was stable for the first 17 days and then decreased, whereas most of the sodium, ammonium-nitrogen, and chloride were no longer leached by 24 days. The VC and TC/VC combinations did not affect cucumber seed germination rate, seedling survival rate, seedling height, and leaf greenness (SPAD) as compared with CF. The stem length, leaf number, dry weight (DW), root index, and SPAD readings of cucumber transplants increased with increasing TC and VC fertilizer applications. The TC/VC combinations increased the biomass of cucumber transplants compared with CK, and did not differ from CF. The results of this study indicated that the 28.32 lb/yard³ of VC (high rate) or the 9.44 lb/yard³ of VC combined with 4 lb/yard³ of TC (medium rate) can be substituted for CF for the cultivation of cucumber seedlings. Based on DW, the 12 lb/yard³ of TC (high rate) or the 4 lb/yard³ of TC combined with 9.44 lb/yard³ of VC (medium rate) fertilizers were suitable replacements for CF for the cultivation of cucumber transplants.

The use of saline irrigation water may be inevitable in the future since the freshwater supply is decreasing over time. In some regions of the United States, producers of both ornamental and agronomic crops are already facing a limited supply of high-quality water. Therefore, it is necessary to determine the salt tolerance of commonly used greenhouse bedding plants to minimize potential salt damage before use of nonpotable water sources is mandated. Research screening several bedding plants has not taken place for more than two decades. Therefore, we undertook experiments to screen popular bedding plants for salt tolerance during greenhouse production. Transplants were exposed to 0 (control), 20, 40, 60, or 80 mm sodium chloride (NaCl) in the irrigation water for 5 weeks resulting in average substrate pour-thru electrical conductivity (EC) values of 4.0 (control), 7.0, 9.8, 12.1, or 14.2 dS·m⁻¹, respectively. Pansy (Viola tricolor) and zinnia (Zinnia angustifolia), the most sensitive species examined, exhibited 100% mortality when exposed to an EC of 14.2 dS·m⁻¹. The least affected species for dry weight (DW) was snapdragon (Antirrhinum majus) with a 54% reduction as EC increased from 4.0 to 14.2 dS·m⁻¹. Only fuchsia (Fuchsia hybrida) and snapdragon were unaffected by an EC of 7.0 dS·m⁻¹, whereas at 9.8 dS·m⁻¹ all of the species had a significantly reduced DW as compared with control plants. Verbena (Verbena ×hybrida), petunia (Petunia ×hybrida), coleus (Solenostemon scutellarioides), and begonia (Begonia hiemalis) were the only species that did not undergo a significant height reduction in comparing 9.8 dS·m⁻¹ to control. A classification of the 14 species is created here on the basis of plant DW to provide guidance as to which species could be irrigated with more saline water while not compromising plant growth and quality.

Seaweed extracts are widely used as plant growth regulators in agriculture and horticulture for improvement of plant growth and development. This study investigated the effects of rockweed (Ascophyllum nodosum) extract application method (foliar spray or substrate drench) and rate on growth and postharvest drought tolerance of petunia (Petunia hybrida) and tomato (Solanum lycopersicum) transplants grown in a commercial peat/perlite substrate. Foliar sprays significantly affected growth of petunia and tomato, but did not improve drought tolerance of petunia and tomato. Whereas, substrate drenches significantly improved drought tolerance of petunia and tomato compared with the control. Shoot fresh weight (FW), shoot dry weight (DW), root index (RI), and chlorophyll index (SPAD) of petunia and tomato increased significantly with increasing concentration of foliar spray rate up to 5 mL·L⁻¹, but did not change significantly with further higher foliar spray rates. Weekly substrate drenches at 20 mL·L⁻¹ significantly decreased FW, DW, RI, and SPAD values of petunia and tomato. In this study, substrate drench at 5–10 mL·L⁻¹ significantly increased flower number of petunia and tomato. The results of this study suggested that substrate drenches at 5–10 mL·L⁻¹ are appropriate for the improvement of postharvest life of petunia and tomato transplants, and that foliar applications can increase plant growth.

The objective of this study was to evaluate the growth and flowering of petunia (Petunia ×hybrida) transplants in response to seven commercial substrates with two water sources (fertigation and clear water irrigation). Seven commercial substrates used were Sunshine #1 Natural & Organic (SS), Metro-Mix 360 (MM), AgriTech (AT), Cornell Peat-Lite Mix B (CB), Jeff’s Organic (JO), LM-18, and LM-111. The experiment was a completely randomized 2 × 7 factorial design with six single-pot replications per treatment. With fertigation, substrate electrical conductivity (EC) decreased over time to 38 days after transplanting (DAT), and then did not further change. The AT substrate EC value was greater than others during the first 38 DAT. With clear water irrigation, substrate EC decreased over time to 31 DAT, and then did not further change. The AT substrate EC value was greater than other substrates during the entire petunia growth period. With fertigation, all substrate pH values were between 6.5 and 7.5 except AT and CB. The AT substrate had the greatest pH ranging from 7.5 to 8.0 during the petunia growth period. The CB substrate exhibited the lowest pH, which was between 5.8 and 6.3. Clear water irrigation had greater substrate pH values than fertigation. There was a substrate and water interaction for calcium (Ca), potassium (K), ammonium-nitrogen (NH₄ ⁺-N), nitrate-nitrogen (NO₃ ⁻-N), and sodium (Na) concentrations in substrate leachate. At 52 DAT, the shoot dry weight (DW), root index (RI), and flower number of petunia grown in AT substrate were greatest among all the substrates, but chlorophyll index (SPAD) was the lowest under either the fertigation or clear water irrigation treatments. The DW and RI of petunia grown in AT substrate were greater when fertigation was used than clear water irrigation, but the water source had no effect on flower number. For SS, MM, CB, JO, LM-18, and LM-111 substrates, fertigation increased petunia DW, RI, and flower number as compared with clear water irrigation, but not SPAD readings.

The 4R nutrient stewardship framework presents four concepts to consider when applying fertilizers in a responsible matter; the “right source” of nutrients should be applied at the “right rate” during the “right time” and supplied to the “right place” to ensure their uptake. In this article, we provide ideas to consider when attempting to provide nutrients at the right time. When nutrients are applied at a time when they are not required by the plant, the result can be economic and environmental losses. Oversupply relative to plant demand can result in losses of applied nutrients because of leaching or volatilization. Undersupply relative to demand, especially in the case of phloem-immobile nutrients, may limit plant growth and yield. Several factors interact to affect plant nutrient demand such as growth stage, life history (annual vs. perennial), environmental conditions, and plant health. Techniques such as soil and tissue testing, isotopic labeling, and spectral reflectance have been used with varying degrees of success and expense to measure plant nutrient demand and guide fertilizer decisions. Besides knowledge of plant nutrient demand, efficient nutrient supply also depends on systems that allow precise spatial and temporal delivery of nutrients. Future improvements to the timing of nutrient delivery will depend on improvement in knowledge of plant nutrient demands. For example, targeted gene expression chips show promise for use in rapidly assessing plant status for a broad suite of nutrients. Future developments that allow more precise nutrient delivery or more robust agroecosystems that scavenge available nutrients before they are lost to the environment will also help producers use nutrients more efficiently.

In the United States, overhead irrigation is common to apply water and dissolved nutrients to vegetable transplants during greenhouse production. Overhead irrigation allows for the control of salt accumulation in the growing medium because excess water can leach salts out of the container. Alternatively, subirrigation saves labor and improves water use efficiency, but soluble salts can accumulate in the upper profile of the containers. Consequently different sets of fertilizer and electrical conductivity (EC) guidelines are required for overhead and subirrigation systems. The objective of this project was to determine the influence of fertilizer concentration and irrigation method (subirrigation vs. overhead irrigation) on the growth of several vegetable transplant crops intended for retail sale. Seedlings of collards (Brassica oleracea var. acephala ‘Vates’), kale (B. oleracea var. acephala ‘Nagoya Mix’), lettuce (Lactuca sativa ‘Buttercrunch’), pepper (Capsicum annuum ‘Sweet Banana’), and tomato (Solanum lycopersicum ‘Sweet 100’) were transplanted into 4-inch-diameter containers and grown in a greenhouse for 4 weeks. Irrigation was provided via ebb and flow benches (subirrigation) or hand-watering (overhead irrigation). Plants received a complete fertilizer solution provided at a concentration of 50, 100, 200, 350, and 500 mg·L⁻¹ nitrogen (N). The treatments resulting in maximum shoot dry weight (DW) for overhead irrigated plants were 100 mg·L⁻¹ N for pepper, 200 mg· L⁻¹ N for tomato, and 350 mg·L⁻¹ N for collards, kale, and lettuce. Irrigation method and fertilizer treatment significantly affected fresh weight (FW) and DW for kale, lettuce, and pepper. For kale and lettuce, regression analysis indicated that maximum DW was reached at a lower fertilizer concentration with overhead irrigation than subirrigation. The treatments resulting in maximum DW for subirrigated plants were 200 mg·L⁻¹ N for kale, lettuce, pepper, and tomato and 350 mg·L⁻¹ N for collards. Reducing fertilizer concentration was an effective method for controlling plant height for all crops we examined except for ‘Sweet Banana’ pepper. However, in many cases height control via nutritional limitation comes at substantial expense to other growth parameters. Our results suggest that, in some cases, fertilizer concentration guidelines for overhead irrigation can be reduced when growing vegetable transplants with subirrigation due to reduced leaching of nutrients and greater potential for accumulation of fertilizer salts.