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  • Author or Editor: Jonathan M. Frantz x
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Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. ‘Designer Dark Red’ geraniums (Pelargonium ×hortorum Bailey) were grown in three experiments to assess possible effects of light on SPD and phosphorous (P) uptake. The first experiment tested the effect of four light intensities (105, 210, 575, and 1020 ± 25 μmol·m−2·s−1) on substrate acidification. At 63 days, substrate pH declined from 6.0 to 4.8 as light intensity increased. Tissue P of plants grown at the highest two light levels was extremely low (0.10%–0.14% of dry weight). P stress has been reported to cause acidification. Because plants in the two lowest light treatments had adequate P, it was not possible to determine if the drop in substrate pH was a direct light effect or a combination of light and P. The second experiment used a factorial combination of the three highest light levels from Expt. 1 and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L−1 substrate) to assess this question. When tissue P concentrations were deficient, pH decreased by 0.6 to 1.0 pH units within 2 weeks and deficiency occurred more often with high light intensity. These data indicated that P deficiency caused substrate acidification and indicated the possibility that P uptake was suppressed by high light intensity. The third experiment was conducted in hydroponics to determine the direct effect of high light intensity on P uptake. In this experiment, cumulative P uptake per gram root and the rate of P uptake per gram root per day both decreased 20% when light intensity increased from 500 to 1100 μmol·m−2·s−1. It is clear from this study that P deficiency causes geraniums to acidify the substrate and that high light suppresses P uptake.

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Unique growing containers and nontraditional types of plant presentation may lead to new production problems for growers. This study was conducted to evaluate the growth of a popular container plant, calibrachoa (Calibrachoa ×hybrida), produced in hanging flower pouches using different growing substrate compositions, polymer amendments, and the layering of substrate types of differing moisture holding capacity with the goal of achieving more uniform plant growth and improved after-sale maintenance. Plastic cylindrical hanging pouches were filled with one of nine hydrated substrate types or combinations. Rooted cuttings of ‘Colorburst Violet’ calibrachoa were planted as indicator plants to identify treatment effects because of their susceptibility to iron deficiency-induced chlorosis of new leaves. Daily measurements of substrate moisture were taken to determine the need for irrigation. Chlorophyll content was estimated nondestructively with a hand-held chlorophyll meter to determine the impact of moisture content. Light, porous substrates resulted in the most uniformly green plants and high numbers of flowers from top to bottom. A layered pouch with heavy, compost-amended substrate above a light, porous layer also produced high-quality, uniform plants. This enabled water to be distributed more uniformly throughout the container volume. This study provides fundamental information on how container geometry and soil moisture retention can influence water management decisions by the grower.

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Greenhouses are used in many climates for season extension or year-round production and can be expensive to heat. Greenhouse users and growers are often faced with management decisions that rely on an understanding of how temperature settings, heating systems, fuel types, and construction decisions influence overall heating costs. There are no easy-to-use programs to calculate heating costs associated with these factors over full cropping seasons. A computer program called Virtual Grower was created that helps calculate heating costs at many U.S. sites. The program uses a weather database of typical hourly temperature, light, and wind information of 230 sites from the National Renewable Energy Laboratory in the calculations. A user can define unique design characteristics such as building material and construction style. The user also defines the type of heating system and heating schedule, and then the program will predict heating costs based on typical weather at the selected location. Shorter-term predictions with weather forecasts of 2 days or less can be made with the software if there is an internet connection through integration with local weather forecasts. Virtual Grower can serve as a platform from which many other features can be added, such as plant growth and scheduling. Continued development will improve the software and allow users to perform baseline analysis of their heating costs, identify areas in their production to improve efficiency, and take some of the guesswork out of energy analysis in unique greenhouses.

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Traditional overhead lighting of dense crop stands in controlled environments favors development of upper leaf layers to maximize interception of light incident at the top of the foliar canopy. The resultant mutual shading of lower leaves in the understory of the canopy can severely limit productivity and yield of planophile crops. Intracanopy lighting alleviated the effects of mutual shading in dense, vegetative stands of cowpea [Vigna unguiculata (L.) Walp ssp. unguiculata] growing in a controlled environment by sustaining irradiance within the understory throughout development of this edible-foliage crop. For an overhead lighting system, photosynthetic photon flux (PPF) in the understory was reduced to 1% of its initial value by 35 days of growth. PPF in an intracanopy-lighted stand remained within 30 μmol·m-2·s-1 of initial values throughout the 50-day cropping period. Spectral distribution of radiation within the intracanopy-lighted stand also remained relatively constant throughout canopy development. In the overhead-lighted stand, violet and blue radiation in the understory decreased as much as 60% from initial values. Stability of the radiation environment within the intracanopy-lighted stand delayed leaf senescence 27 days beyond when interior leaves of the overhead-lighted canopy began to turn yellow on day 16. The intracanopy-lighted stand produced twice as much edible biomass per unit electrical energy consumed by lamps as for the overhead-lighted system. The treatment differences were due to the continuous presence of understory irradiation when using intracanopy lighting but not when using overhead lighting, and they underscore the importance of the entire foliar canopy in realizing the full productivity potential of dense crop stands in controlled environments.

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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.

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An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add significantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca2+ and Mg2+). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported beneficial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species [pansy (Viola ×wittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)] was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain reflectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, flower number, flower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed significant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was significantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total flower numbers and flower longevity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefits from hydrogels confirms the potential benefit early in production with little to no benefit later in production and in post-production. These data will assist growers in determining if the benefits derived from the use of PAM justify the added cost of medium.

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Geranium (Pelargonium ×hortorum) typically follows the C3 metabolic pathway. However, it switches to CAM metabolism under certain abiotic stress environments. This switch may affect the nutritional requirement and appearance of visible deficiency symptoms of these plants. Because potassium (K) plays a key role in stomatal function, K-deficiency was studied in geranium. Plants were grown hydroponically in a glass greenhouse. The treatments consisted of a complete, modified Hoagland's solution with millimolar concentrations of macronutrients, 15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S and micromolar concentrations of micronutrients, 72 Fe, 9.0 Mn, 1.5 Cu, 1.5 Zn, 45.0 B, and 0.1 Mo, and an additional solution devoid of K. It took longer to develop the classic K deficiency symptoms than other bedding plant species commonly require. The K-stress plants' dry weight was 10% and 37% of control at incipient and advanced stage, respectively. When portions of geranium leaves were covered, symptomology on leaves with K stress developed rapidly (within 2 days) compared to the uncovered portion of the leaf blade. Control plants contained an abundance of marble-shaped K crystals in the adaxial surface of leaf mesophyll, but were lacking in the K-deficient plants. Geranium is more prone to K stress during short days than long days and an additional supply of K would be needed for normal growth in short days.

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Silica (Si) is not considered to be an essential plant nutrient because without it, most plants can be grown from seed to seed without its presence. However, many investigations have shown a positive growth effect if Si is present, including increased dry weight, increased yield, enhanced pollination, and most commonly, increased disease resistance, which leads to its official designation as a beneficial nutrient. Surprisingly, some effects, such as reduced incidence of micronutrient toxicity, appear to occur even if Si is not taken up in appreciable amounts. The literature results must be interpreted with care, however, because many of the benefits can be obtained with the counterion of the Si supplied to the plant. Determining a potential benefit from Si could be a large benefit to greenhouse plant producers because more production is using soilless media that are devoid of Si. Therefore, Si must be supplied either as a foliar spray or nutrient solution amendment. We investigated adding Si to New Guinea Impatiens (Impatiens hawkeri Bull), marigold (Tagetes erecta), pansy (Viola wittrockiana), spreading petunia (Petunia hybridia), geranium (Pelargonium spp.), and orchid (Phalaenopsis spp.). Using SEM, energy dispersive X-ray analysis, and ICP analysis, Si content and location was determined. This information and other growth characteristics will be used as a first step in determining the likelihood of using Si as a beneficial element in greenhouse fertilizer solutions for higher quality bedding plants with fewer agrochemical inputs.

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Controlled-release fertilizers (CRFs) have not been extensively used in floricultural production, perhaps due to lack of grower experience and research-based information with their use in herbaceous plant production. Any information about the correct use of CRF should increase growers’ confidence in using this type of fertilizer. The objective of this research was to compare the growth and quality of bedding impatiens (Impatiens wallerana XTREME™ ‘Scarlet’) when grown with typical water-soluble fertilizer (WSF) and with different combinations of longevity and rates of a single formulation of CRF. The CRF 16N–3.9P–10K consisted of different longevities (3–4, 5–6, 8–9, or 12–14 months) and application rates (1.4, 3.4, 6.8, 10.2, or 13.6 kg·m−3). Plants were grown in the greenhouse, and consumer evaluations were performed at market maturity. Plant canopy cover, flower cover (FC), and shoot dry weight (DW) were also determined. Commercially acceptable plant quality was achieved with CRF application rates between 3.4 and 6.8 kg·m−3. At low CRF application rates, the faster release rate (shorter longevities) CRFs produced larger plants [DW and leaf canopy cover (LCC)] with greater flowering potential (FC) than slower release rate CRFs. At higher application rates, slower release rates (longer longevities) outperformed the faster release CRFs for the same parameters. CRF-grown plants were smaller than WSF plants when CRFs were applied at the lowest rates. No differences in any of the three variables measured were found when plants were grown at a rate of 6.8 kg·m−3 CRF of any longevity or with WSF. Growers should adjust CRF application rates according to CRF longevity.

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The productivity of lettuce in a combination of high light, high temperature, and elevated CO2 has not been commonly studied because rapid growth usually causes a calcium deficiency in meristems called tipburn, which greatly reduces quality and marketability. We eliminated tipburn by blowing air directly onto the meristem, which allowed us to increase the photosynthetic photon flux (PPF) to 1000 μmol·m-2·s-1 (57.6 mol·m-2·d-1); two to three times higher than normally used for lettuce. Eliminating tipburn doubled edible yield at the highest PPF level. In addition to high PPF, CO2 was elevated to 1200 μmol·m-2·mol-1, which increased the temperature optimum from 25 to 30 °C. The higher temperature increased leaf expansion rate, which improved radiation capture and more than doubled yield. Photosynthetic efficiency, measured as canopy quantum yield in a whole-plant gas exchange system, steadily increased up to the highest temperature of 32 °C in high CO2. The highest productivity was 19 g·m-2·d-1 of dry biomass (380 g·d-1 fresh mass) averaged over the 23 days the plants received light. Without the limitation of tipburn, the combination of high PPF, high temperature, and elevated CO2 resulted in a 4-fold increase in growth rate over productivity in conventional environments.

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