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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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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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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.

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Abdulrhman I. Al-hemaid and David S. Koranski

Petunia `Red Flash', Vinca `Little Blanch', Pansy `Magestic Giant Purple', and Impatien `Super Elfin Red' plugs were held in the greenhouse after they reached the saleable size in 200, 406, 512, and 800 for 1 to 3 weeks Pansy plugs were held in coolers at 40, 50, or 60F under fluorescent light for 16 hrs photoperiod for 1 to 3 weeks in 200, 406, 512, or 800 plug trays. All plants ware transplanted weekly and were grown in the greenhouse until flowering and data were collected. For plants bald in the greenhouse, plants were affected by transplanting time. As the holding time increased the final height, diameter, flower number, and fresh and dry weight of plants decreased. The flowering time was delayed by increase the holding time, regardless of plant variety, As cell size decreased, plant height, diameter, flower number, and fresh and dry weight decreased. For plants held in the coolers, the flowering time was delayed by the transplant time, regardless of cooler temperatures Plant quality was not affected by the treatment. The height, diameter, flowers number, and fresh and dry weight of plants showed a little effects by temperatures, cell size, and transplanting time.

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Abdulrhman I. Al-hemaid and David S. Koranski

Petunia `Red Flash', Vinca `Little Blanch', Pansy `Magestic Giant Purple', and Impatien `Super Elfin Red' plugs were held in the greenhouse after they reached the saleable size in 200, 406, 512, and 800 for 1 to 3 weeks Pansy plugs were held in coolers at 40, 50, or 60F under fluorescent light for 16 hrs photoperiod for 1 to 3 weeks in 200, 406, 512, or 800 plug trays. All plants ware transplanted weekly and were grown in the greenhouse until flowering and data were collected. For plants bald in the greenhouse, plants were affected by transplanting time. As the holding time increased the final height, diameter, flower number, and fresh and dry weight of plants decreased. The flowering time was delayed by increase the holding time, regardless of plant variety, As cell size decreased, plant height, diameter, flower number, and fresh and dry weight decreased. For plants held in the coolers, the flowering time was delayed by the transplant time, regardless of cooler temperatures Plant quality was not affected by the treatment. The height, diameter, flowers number, and fresh and dry weight of plants showed a little effects by temperatures, cell size, and transplanting time.

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Sandra Menasha, Milton Tignor, and David Heleba

Transplanting sweet corn is commonly practiced in the northeast U.S. to improve stand establishment and promote early harvest. However, early spring storms and labor constraints can delay transplanting when establishment is most desirable. `Temptation' sugary enhanced (se) sweet corn transplants 0-, 2-, 4-, 6-, and 8-days-old beyond the “grower” 2-week growth period were field planted to explore the effects delayed planting combined with plug cell volume differences would have on transplant ear quality and early yields. The transplant treatments were evaluated in a two-way factorial (five delayed planting dates × three plug volumes) arranged in a split-plot design with five replications. Field sites were the whole plot treatment and the factorial treatments were the split-plots. All transplants were planted on 24 May 2004 at the two field sites. The final density was ≈22,000 plants/acre. Transplant cell volume (15, 19, and 29 mL) had no significant effect on ear quality and total marketable yield. Ear length was significantly affected by field site (P≤ 0.0001) and ear diameter was significantly affected by planting delay (P= 0.0145). Field site (P≤ 0.0001) and planting delay (P= 0.0090) both significantly affected the number of early marketable ears/acre. The results indicate that transplants can remain in the plug cells up to 20 days (2 weeks + 6 day delay) before the delay negatively impacts ear diameter, tip fill, and early marketable yield.

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K. Francis Salifu, Douglass F. Jacobs, Guillermo Pardillo, and Mary Schott

We examined growth and nitrogen (N), phosphorus (P), potassium (K), and microelement nutrition of grafted black walnut (Juglans nigra L.) seedlings exposed to increasing nutrient supply and grown in the greenhouse for 18 week. Plants were potted and grafted within the first 4 week, then fertigated once each week for a 7-week period with a varying nutrient solution of 20N–4.4P–16.6K that delivered 0, 1160, 2320, and 4620 mg N/plant. Plants were harvested at week 18. There was a positive mean growth response to increased fertilization, although trends were statistically similar across treatments. Leaf nutrient concentration ranged from 22 to 31 g · kg–1 N, 5 to 14 g · kg–1 P, and 19 to 25 g · kg–1 K. The 2320 mg N/plant treatment increased leaf nutrient content 18% to 86% for N, 33% to 303% for P, and 23% to 58% for K compared with the control. Nitrogen efficiency decreased with increased N supply. Increased nutrient retention in the growing medium at higher fertility suggests root plugs could serve as immediate critical nutrient sources for grafted black walnut seedlings after outplanting. Study results suggests nursery fertilization can be used to improve the nutritional quality of grafted black walnut as well as store nutrients in root plugs for later utilization to benefit early establishment success.