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Ronald W. Garton and Irvin E. Widders

Seedlings of processing tomato `H 2653' (Lycopersicon esculentum Mill.) were cultured in 288-cell (< 6 cm3 volume) plug trays in a soilless growing medium. Pretransplant fertilization with nutrient solutions containing 10 or 20 mm N and 2 or 5 mm P for 10 days altered the total ammoniacal-N and P, and the soluble NO3-N and PO4-P concentrations in the shoot tissue at transplanting. Post-transplanting shoot and root growth were more rapid in late May plantings than in earlier plantings. The 20-mm N and 2-mm P pretransplant treatment caused the most rapid shoot growth following early season plantings in the field. Rapid seedling establishment after transplanting was generally not a good indicator of potential fruit yield. The 5-mm P pretransplant treatment produced higher marketable fruit yields in early plantings but not in later. Culture of seedlings under a low fertilization regime (5.4 mm N, 1.0 mm P, and 1.6 mm K) before pretransplant treatment produced as high or higher fruit yields than did seedlings from a higher regimen. Withholding fertilizer temporarily before transplanting resulted in a depletion in tissue N and P concentrations, slow post-transplanting shoot growth, and lower yields.

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Yoshiaki Kitaya, Genhua Niu, Toyoki Kozai, and Maki Ohashi

Lettuce (Lactuca sativa L. cv. Summer-green) plug transplants were grown for 3 weeks under 16 combinations of four levels (100, 150, 200, and 300 μmol·m-2·s-1) of photosynthetic photon flux (PPF), two photoperiods (16 and 24 h), and two levels of CO2 (400 and 800 μmol·mol-1) in growth chambers maintained at an air temperature of 20 ±2 °C. As PPF increased, dry mass (DM), percent DM, and leaf number increased, while ratio of shoot to root dry mass (S/R), ratio of leaf length to leaf width (LL/LW), specific leaf area, and hypocotyl length decreased. At the same PPF, DM was increased by 25% to 100% and 10% to 100% with extended photoperiod and elevated CO2 concentration, respectively. Dry mass, percent DM, and leaf number increased linearly with daily light integral (DLI, the product of PPF and photoperiod), while S/R, specific leaf area, LL/LW and hypocotyl length decreased as DLI increased under each CO2 concentration. Hypocotyl length was influenced by PPF and photoperiod, but not by CO2 concentration. Leaf morphology, which can be reflected by LL/LW, was substantially influenced by PPF at 100 to 200 μmol·m-2·s-1, but not at 200 to 300 μmol·m-2·s-1. At the same DLI, the longer photoperiod promoted growth under the low CO2 concentration, but not under the high CO2 concentration. Longer photoperiod and/or higher CO2 concentration compensated for a low PPF.

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Jin-Sheng Huang and Paul V. Nelson

Salinity guidelines for seed germination substrates are extremely low and difficult to attain given the salinity contributions of components such as peatmoss, vermiculite, limestone, wetting agent, and nutrients. This study was conducted to determine the value of N, P, K, and S as pre-plant nutrients with the anticipation that some could be eliminated. Seed were sown in two similar experiments on 23 Mar. and 6 June 1995 in 288-cell plug trays containing a substrate of 3 sphagnum peat: 1 perlite (v/v) amended with 6 g dolomitic limestone and 1.5 g Esmigran micronutrient mix per liter. Test plants included impatiens `Accent Rose' (Impatiens wallerana L.) and gomphrena `Buddy' (Gomphrena globosa. L.) Six preplant treatments including none, all, or all minus one of the nutrients N, P, K, and S were applied, each at a rate of 100 mg·L–1, substrate, in a randomized complete-block design with three blocks. Post-plant fertilization with 13–0.9–10.8 at 50 mg N/L began 1 week after sowing and was increased to 100 mg N/L when the fourth true leaf appeared. Omission of pre-plant K and S did not result in any reduction in final plant size in impatiens and only a minor reduction in one of the two gomphrena crops. Omission of N and P consistently reduced final size of plants by a commercially significant amount. While K and S are not necessary, N and P should be considered in a pre-plant fertilizer for these crops. In each situation where shoot size was smaller the root/shoot ratio was unchanged.

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Marc van Iersel

Various growth stimulators have been reported to improve plant growth. Some of these are formulated to improve root growth, which would be particularly beneficial for reestablishing transplants. Three commercially available plant growth stimulators—PGR IV (MicroFlo, Lakeland, Fla.), Roots2 (Lisa Products Corp., Independence, Mo.), and Up-Start (The Solaris Group, San Ramon, Calif.)—were tested to quantify their effect on post-transplant growth of petunia (Petunia × hybrida Hort. Vilm.-Andr.) and impatiens (Impatiens wallerana Hook.f.) seedlings and to assess their value for the greenhouse industry. Seedlings were transplanted from plug flats into larger 5.6-fl oz (166-cm3) containers and treated with 1.1 fl oz (31 mL) of growth stimulator per plant (22 fl oz/ft2). Applications were made immediately after transplant. None of the treatments affected root mass at any time. Up-Start (2 fl oz/gal) increased final shoot dry mass by ≈20% compared to the control plants. The increase in shoot growth by Up-Start most likely is caused by the fertilizer it contains. Up-Start also increased flowering of petunia from 34 to 40 days after transplant. PGR IV (0.5 fl oz/gal) and Roots2 (1.28 fl oz/gal) did not affect dry mass of the plants. PGR IV increased the number of flowers of petunia and impatiens, but this effect occurred well after the plants were marketable. Roots2 caused a small delay in early flowering and an increase in late flowering of petunia but had no effect on flowering of impatiens. Since the effects of the growth stimulators was either due their fertilizer content (Up-Start) or occurred after the plants would have been sold (PGR IV, Roots2), none of the growth stimulators appears to be beneficial for bedding plant producers.

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Beth E. Engle, Arthur C. Cameron, Royal D. Heins, and William H. Carlson

Storage of perennial plugs at subfreezing temperatures could be a valuable production tool since plants could be removed over relatively long periods for forcing. Several species of seed-propagated perennial plugs were pretreated at 0 and 5C under continuous 50 μmol·s-1m-2 PPF for 0, 2, 4, or 8 weeks. After each pretreatment period, plugs were placed into 4-mil polyethylene bags that were then sealed and placed at -2.5C for 0, 2, or 6 weeks. Plugs were then removed from the bags and placed into a 24C greenhouse for two weeks under ambient light levels and daylength, after which time they were rated for percent survival and general regrowth quality. Regrowth was not influenced by pretreatment temperature. Regrowth of Limonium dumosumtatarica, and Campanula carpatica `Blue Clips' following -2.5C storage was excellent with or without a pretreatment. Regrowth of Achillea filipendulina `Cloth of Gold,' Gaillardia grandiflora `Goblin,' and Iberis sempervirens `Snowflake' was improved on plugs given the 0 or 5C pretreatment. Hibiscus × hybrida `Disco Belle Mixed' regrowth was poor, regardless of pretreatment.

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Thomas H. Boyle

Binomial probability distributions were used to determine the effects of percent seed germination and number of seeds sown per cell on expected numbers of seedlings in plug trays. Expected numbers of empty cells in five types of plug trays (128, 273, 338, 406, and 512 cells/tray) were calculated for cases where one to seven seeds were sown per cell and seed germination ranged from 50% to 95%. Generally, one additional seed was required per plug cell for each 10% decrease in the germination percentage in order to attain the same number of filled cells per plug tray. Expected frequencies were calculated for the number of seedlings in plug trays when one to five seeds were sown per cell and seed germination ranged from 50% to 95%. When the number of seeds sown per cell remained constant, uniformity in seedling number per cell increased as the germination percentage increased. When percent seed germination remained constant and the number of seeds sown per cell was increased, the percentage of cells with at least one seedling increased, whereas the uniformity in seedling number per cell decreased. Additional examples are presented in the article on the utility of binomial distributions in determining expected number of seedlings.

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Paul T. Karlovich and David S. Koranski

Fifteen lots of impatiens representing five cultivars were used to evaluate the potential of a soak test for predicting the performance of impatiens seeds in plug-production systems. This test would be valuable in breeding programs because it is non-destructive, seed-specific, inexpensive, fast, and does not require large numbers of seed. The soak test submerged individual seeds in one ml distilled water during germination. The results of this test were compared to standard blotter germination and to plug tray performance in the Iowa State University greenhouse and at two commercial greenhouses. Different responses to the soak test were found among lots and cultivars but the differences could not be correlated to the plug tray performance of the seeds. The responses to the soak test do not appear to be genetically related for these cultivars.

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Efstratia Papanikou and Paul H. Jennings

Previous research has shown that low-temperature storage can be used to maintain bedding plants in plug trays when weather conditions in spring make scheduling of transplanting difficult. The objective of this study was to determine what physiological changes occur during the short-term, low-temperature storage of plug seedlings. Plants of two bedding plant species, Geranium and Vinca, were stored at 2, 6, or 10°C and under low light or dark conditions for 4 weeks. Data were collected at three sampling dates (0, 2, or 4 weeks after beginning of storage) and included dry and fresh mass, total leaf area, leaf chlorophyll content and chlorophyll fluorescence as well as electrolyte leakage and soluble sugar content of leaf and root tissue. The parameters will be discussed in relationship to plug seedling survivability, quality, and growth responses under the experimental storage treatments.

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Jin-Sheng Huang, Paul V. Nelson, Douglas A. Bailey, William C. Fonteno, and Nancy C. Mingis

Salinity guidelines for seed germination substrates call for low, difficult to attain levels. This study was conducted to determine the value of N, P, K, and S as preplant nutrients, with the anticipation that some could be eliminated to alleviate the high salinity problem in many substrates. Impatiens wallerana L. `Accent Rose' and Gomphrena globosa L. `Buddy' were tested in 288-cell plug trays containing a substrate of 3 sphagnum peat moss: 1 perlite (v/v) in two experiments. Seven preplant N, P, K, and S treatments, including none, all (each at 100 mg·L-1 of substrate), all minus one of each of the nutrients, and N at one additional rate of 50 mg·L-1, were tested. Postplant fertilization was applied to all treatments as 13 N-0.9P-10.8K at 50 mg·L-1 N beginning 1 week after sowing and was increased to 100 mg·L-1 N when the fourth true leaf appeared. The resultant seedlings were transplanted into 48-cell flats and grown into marketable stage for further evaluation. For maximum potential growth, N, P, K, and S were needed as preplant fertilizer. However, compact shoots, not maximum growth, are generally desired in commercial production. Thus, K and S can be omitted since their contribution to growth was only occasional and small. To further ensure a consistently desirable level of compactness, it was necessary to omit N or P or both in addition to K and S. Omission of N alone yielded the most desirable compact plant qualities, including suitable reduction in final seedling size. Omission of P alone yielded larger reductions in height and shoot dry weight of seedlings compared to N omission, and a delay of 2 to 4 days in flowering of bedding plants. Omission of the four nutrients, compared to -P, resulted in similar seedling growth reduction and bedding plant flower delay. Since N omission lowered the salt (electrical conductivity) level of substrate more than P omission and had no negative impact on subsequent bedding plant flowering compared to the other two treatments, N omission would be the more desirable of the three. However, N omission resulted in chlorotic seedlings, but these quickly turned green upon restoration of N. Omission of P or all four nutrients resulted in desirably deep green seedlings. Growth of gomphrena seedlings, a high-fertilizer requirement category of taxa, was suppressed when the preplant rate of N was 50 mg·L-1 compared to 100 mg·L-1, while growth of impatiens, a low-fertilizer requirement category of taxa, was essentially equivalent at these rates. Preplant additions of nutrients applied at 100 mg of nutrient element per liter of substrate lasted for the following numbers of days; NO3-N, 18-25 days; NH4-N, 12-20 days; K2O, 27 days; PO4-P, >35 days; and SO4-S, >35 days.

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Holly L. Scoggins, Douglas A. Bailey, and Paul V. Nelson

Methods for extracting growing substrate root-zone solution include the saturated media extract (SME) and the 2 water: 1 substrate (v/v) suspension, neither of which are particularly suited to bedding plant plug systems. We have developed the press extraction method (PEM) as a simple and quick alternative to these methods. The grower simply collects a representative sample of plug trays and presses the top of the plug, collecting the expelled solution. Solution pH and EC can be measured immediately and the sample then sent to an analytical laboratory for nutrient analysis. Initial experiments demonstrated that differing manual pressures did not affect solution chemical properties. The PEM then was compared to the SME and 2:1 methods over a range of fertilizer levels and with peat- and coir-based substrates. Within substrates, pH, EC, and macronutrients were similar between the PEM and the SME. The level of dilution inherent in the 2:1 method resulted in much lower EC and nutrient levels when compared to the other two methods. Further experiments compared the PEM to the SME and 2:1 on plug flats collected from several commercial greenhouses and also those grown in the research greenhouse. The wide range of bedding plant species and fertility levels tested introduced variation needed to develop regression equations and correlations to create quantitative interpretation ranges for the PEM based on previously published sufficiency ranges for the SME and 2:1.