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Jong-Goo Kang and Marc van Iersel

Fertilizer recommendations for fertilizing bedding plants are normally based on nitrogen content of the fertilizer solution. However, nutrient availability is more closely related to the concentration of nutrients in the growing medium than the concentration in the fertilizer solution. Environmental conditions can affect the accumulation of nutrients in the growing medium and optimal fertilizer concentrations are likely to depend on environmental conditions. To test this hypothesis, we grew petunias and geraniums under three temperature regimes (35 °C/27C, 25 °C/17C, and 15 °C/7 °C) and with five concentrations of fertilizers [electrical conductivity (EC) of 0.15, 1, 2, 3, and 4 dS·m–1]. Temperature and fertilizer EC affected the plant growth. Optimal fertilizer EC decreased as temperature increased. Growth was better correlated with EC of the growing medium than with EC of the fertilizer solution. Irrespective of growing temperature, plant growth was best when EC of the growing medium was between 3 and 4 dS·m–1. A lower growing medium EC slowed down growth, presumably because of mild nutrient deficiencies. Higher fertilizer concentrations in the growing medium (>4 dS·m–1) decreased growth because of salt stress. The EC of the growing medium increased with increasing EC of the fertilizer solution and with increasing temperature. Because of the interactive effect of fertilizer concentration and temperature on the EC of the growing medium, plants should be grown with more dilute fertilizer solutions at higher temperatures. Fertilization guidelines for growers should be based on maintaining the EC of the growing medium within an optimal range instead of the more traditional recommendations based on the concentration of the fertilizer solution.

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Valerie M. Jonas and Kimberly A. Williams

A series of experiments were conducted to determine the ranges of irrigation frequency and N and P fertilization regimes that produce ivy geranium (Pelargonium peltatum L.) plants of optimum commercial quality. Two cultivars, `Sybil Holmes' and `Amethyst', were grown. Data collected included fresh and dry weights, ratings, leaf area, height, width, ratings, and nutrient tissue content. Individual pots were weighed daily and irrigated when weight of pots dropped by 15%, 30%, 45%, or 60% of container capacity (CC). Leaf water potential was measured using a pressure chamber. At both mid and end of crop, plants irrigated when pot weight dropped by 30% of CC were under least water stress (e.g., water potential of –7.0 to –4.7 MPa). Irrigation frequencies at 15%, 45%, or 60% of CC had similar water potentials (e.g., –9.9 to –9.1 MPa). At 15%, a plausible explanation of the stress is that oxygen was limiting in the root zone due to water-logging; at 45% and 60%, water was the limiting factor. Single factor experiments with N at five concentrations ranging from 2 to 32 mm and P at five concentrations ranging from 0.08 to 2.56 mm were conducted. Quadratic equations were fit to curves of growth responses plotted against concentration of N or P applied. As an example of results, N fertilizer rates of 16 and 32 mm for `Amethyst' resulted in similar, commercially acceptable dry weights (37g), but different N tissue concentrations of 3.4% and 3.9% respectively. For `Sybil Holmes', N fertilizer rates of 10 and 26 mm resulted in similar dry weights (21g) but different tissue concentrations of 2.8% and 3.4%, respectively.

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S.A. Carver, H.K. Tayama, T.L. Prince and L.S. Campbell

Results from a preliminary study (growth parameters and foliar analyses) comparing a new specialty Osmocote formulation (12N-5.5P-12.4K) designed specifically for poinsettias with a standard Osmocote formulation (19N-2.6P-9.9K) revealed that the new formulation provided inadequate levels of nutrients at 1.0× and 1.5× the recommended rate. Average plant height (cm) for plants produced with 1.0× 12N-5.5P-12.4K, 1.5× 12N-5.5P-12.4K, 1.0× 19N-2.6P-9.9K was 33, 34, 37. Average plant diameter (cm) and foliar N content (%) was 42, 46, 53, and 2.8, 3.5, 4.1, respectively. Follow up studies (growth parameters and foliar analyses) comparing replacement shipments of three specialty Osmocote formulations (12N-5.5P-12.4K for poinsettias, 12N-4.4P-14.1K for potted chrysanthemums, and 13N-5.5P-9.1K for zonal geraniums) with Osmocote 19N-2.6P-9.9K and Peter's 20N-4.4P-16.6K injected at 200 mg N per liter of water at every irrigation showed all specialty formulations to be adequate sources of plant nutrients-comparable to the standard Osmocote. Average chrysanthemum height (cm) for plants produced with 1.0× 12N-5.5P-12.4K, 1.5× 12N-5.5P-12.4K, 1.0× 19N-2.6P-9.9K, Peter's 20N-4.4P-16.6K was 30, 30, 30, 29. Average chrysanthemum diameter (cm) and foliar N content (%) was 51, 50, 49, 50, and 4.5, 4.8, 4.4, 5.2, respectively.

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Eunhee Kim and Richard H. Mattson

Psychophysiological responses to geranium visual stimuli were analyzed on female college students with low attentiveness. Alpha and fast-beta brain wave activities, electrodermal activities, and skin temperature were measured continuously during a 5-min baseline, a 10-min induced stressor, and a 5-min treatment. Each of 75 female college students viewed a film of a stressful human situation—an induced stressor, then was exposed to a randomly assigned treatment: red-flowering geraniums, nonflowering geraniums, or no plants. Based on responses to the induced stressor, students were placed into non-, mild-, and high-induced stress groups. Regression models of psychophysiological responses to each treatment were developed for over-all stress levels. Non-induced stress female students exposed to red-flowering geraniums in contrast to nonflowering geraniums and no-plants showed greater fast-beta brain wave activity. Greater fast-beta of non-induced stress female students exposed red-flowering geraniums was associated with increased positive attention and not because of increased stressful tension. This conclusion was supported by more positive emotional states self-reported using the Zuckerman Inventory of Personal Reactions. Conclusive findings from over-all stress levels suggest that benefits of viewing red-flowering geraniums occur to both nonstress and high stress female college students; red-flowering geraniums improve positive attention of female students with no stress (low attentiveness) and enhance stress recovery of female students with high stress (tension).

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Wayne A. Mackay, Brent Pemberton, Joseph Maxim and Suresh D. Pillai

without the risk of introducing disease agents that currently are not present in the United States. Experiments were conducted to assess the feasibility of using E-beam irradiation doses of 1 kGy or less as a disinfestation tool for geranium cuttings

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Harry K. Tayama and Stephen A. Carver

A series of crop-specific, resin-coated, controlled-release fertilizer formulations, including: Sierra Geranium Mix 13-12-11 Plus Minors, Sierra Chrysanthemum Mix 12-10-17 Plus Minors, and Sierra Poinsettia Mix 12-12-15 Plus Minors were preplant-incorporated into Metro Mix 350 growing medium for the production of potted zonal geraniums, chrysanthemum, and poinsettia. Plant growth and foliar nutritional responses were compared to those obtained from plants produced with a standard resin-coated, controlled-release Osmocote formulation (19N-6P-12K), water-soluble Peters 20N-10P-20K, and a combination of water-soluble and resin-coated treatments. Crops produced with specialty resin-coated mixes (at recommended rate = l×) were equal in growth and flowering characteristics to those produced with Osmocote (1×), water-soluble (200 ppm nitrogen), or a combination of water-soluble (200 ppm nitrogen) and resin-coated (0.5×) fertilizer treatments. Foliar analyses revealed elemental concentrations in resin-coated fertilizer-treated plants were below those in water-soluble or combination treatments, but were within a range to support satisfactory quality crop production.

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Rajeev Arora, S.P. Dharmalingam and B.C. Bearce

Evidence is accumulating in favor of a linkage at the cellular level between various abiotic stresses. We conducted a study to evaluate the effect of water stress on the heat tolerance of zonal geraniums. Water-stress was imposed as previously described. Leaf water potential (LWP, MPa), relative water content (RWC, percent), and heat-stress tolerance (HST; LT50, defined as temperature causing half maximal percent injury based on electrolyte leakage) were measured in control, stressed, and recovered (watering restored as in controls) plants. Proteins were extracted from the leaves following the treatments. SDS-PAGE and immunoblotting were performed using standard procedures. Immunoblots were probed with antibodies to dehydrin (T. Close) and 70-kDa heat shock cognate (HSC 70 of spinach) proteins (C. Guy). Data indicate that 1) LXWP and RWC in control and stressed plants were –0.378 and –0.804 MPa and 92.31% and 78.69%, respectively; 2) stressed plants exhibited a significant increase in HST compared to control (LT50 of 55°C vs. 51°C), which was associated with the accumulation of several heat-stable, dehydrin proteins (26 to 50 kDa), and of cytosolic and ER luminal (BiP) HSC 70 proteins; 3) in recovered plants, LXWP, RWC, and HST reversed back to the levels of control concomitant with the disappearance or reduction of dehydrins and HSC 70 proteins. These results suggest that specific stress proteins may play a role in development of heat stress tolerance.

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Dawn M. Alleman and Thomas C. Weiler

Four experiments were conducted over 2 years focusing on water and fertilizer delivery methods with emphasis on minimal resource use. Poinsettia `Freedom', `Celebrate 2'. `Peppermint Pink', `Angelika White', `Lilo' and `Angelika Marble' and geranium `Kim', `Aurora', Ritz', and `Melody' cuttings were grown in 6 inch pots with peat-lite mix and were harvested at marketable size. Nitrogen efficiency was compared by replicating each irrigation treatment with soluble fertilizer (SF) and controlled release fertilizer (CRF). Crops grown with SF were started at 225ppm N for several weeks, then finished at 125ppm N after monitored EC had dropped below 1000μS. CRF treatments were potted up with 1.6 total grams of N available to the plant and irrigated throughout production with tap water. Irrigation treatments included: drip tube leaching, drip tube, ebb & flow, trough. trough lined with capillary mat, trough lined with plastic-covered capillary mat, flats of capillary mat, flats with plastic-covered capillary mat. Daily irrigation volumes were recorded. Weekly data collection included EC, pH, nitrate nitrogen. and ammonium nitrogen. Harvest data included plant dry weight, and total nutrient analyses of plants and substrate. Water efficiency was significantly improved in recirculating systems and with capillary mat systems. No significance was noticed in dry weight or final nutrient analyses across treatments. Significance existed in water quality throughout crop production.

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Peter M. Shaw and Rita Hummel

The effects of vesicular-arbuscular mycorrhizae (VAM) on the growth and flowering of Geranium `Sprinter Scarlet' in three greenhouse soilless media were investigated. All media proved to be well suited for geranium growth and VAM had no significant effect on most vegetative parameters. However, VAM significantly reduced the number of days to flowering of plants grown in Mycori-Mix and Sunshine Aggregate #4 by 6.4 and 6.6 days respectively. Plants grown in Mycori-Mix with VAM flowered 99.4 days after sowing, significantly sooner than those grown in the other media with VAM. Mycorrhizal plants in Mycori-Mix and Metro Mix had a greater number of lateral branches >5 cm in length than non-mycorrhizal in the same media. Regardless of VAM treatment, plants grown in Mycori-Mix had a greater number of visible inflorescences at harvest than the other two media.

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Timothy K. Broschat and Kimberly K. Moore

Zonal geraniums (Pelargonium ×hortorum) from seed and african marigolds (Tagetes erecta), which are known to be highly susceptible to Fe toxicity problems, were grown with I, 2, 4, or 6 mm Fe from ferrous sulfate, ferric citrate, FeEDTA, FeDTPA, FeEDDHA, ferric glucoheptonate, or ferrous ammonium sulfate in the subirrigation solution. FeEDTA and FeDTPA were highly toxic to both species, even at the 1 mm rate. Ferrous sulfate and ferrous ammonium sulfate caused no visible toxicity symptoms on marigolds, but did reduce dry weights with increasing Fe concentrations. Both materials were slightly to moderately toxic on zonal geraniums. FeEDDHA was only mildly toxic at the 1 mm concentration on both species, but was moderately toxic at the 2 and 4 mm concentrations. Substrate pH was generally negatively correlated with geranium dry weight and visible phytotoxicity ratings, with the least toxic materials, ferrous sulfate and ferrous ammonium sulfate, resulting in the lowest substrate pHs and the chelates FeEDTA, FeDTPA, and FeEDDHA the highest pH. The ionic Fe sources, ferrous sulfate and ferrous ammonium sulfate, suppressed P uptake in both species, whereas the Fe chelates did not. Fe EDDHA should be considered as an effective and less toxic alternative for the widely used FeEDTA and FeDTPA in the production of these crops.