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Youbin Zheng*, Thomas Graham, Stefan Richard, and Mike Dixon

Pot gerbera (Gerbera jamesonii Var. `Shogun') plants were subirrigated with one of four nutrient solutions (10, 25, 50, and 100% of full strength) in order to determine whether currently used commercial nutrient solution concentrations can be reduced without negative impact on crop production. Nutrient concentration levels did not affect leaf area, flower number and appearance, and plant total dry weight. There were no significant differences in leaf chlorophyll content between the plants that received the 50 and 100% strength nutrient solutions. It is concluded that nutrient solution concentrations typically used in commercial greenhouse, for pot gerbera production, can be safely reduced by at least 50% without adversely affecting crop production. Nutrients accumulated in the top section of the growth substrate under all treatment levels; however, no phytotoxic effect was observed. Fertilizer inputs were reduced in the 50%, 25%, and 10% treatments by 54%, 75%, and 90% respectively. After 4 weeks recirculating, the quality of the nutrient solutions was still within acceptable limits.

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X. Fontanet, V. Estaún, A. Camprubí, and C. Calvet

Prior to the commercial use of arbuscular mycorrhiza (AM) in the nursery, the effects of commonly used pesticides on symbiosis must be evaluated. Metalaxyl and propamocarb are two fungicides added to potting substrates to prevent diseases caused by phycomycetes. Both fungicides were incorporated into the potting substrate before the inoculation and planting of the peach-almond hybrid rootstock GF677 (Prunus persica L. × Prunus dulcis Mill. D.A. Webb). The AM fungus used were Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe and Glomus intraradices Schenck & Smith. Glomus intraradices was not affected by either fungicide; however, metalaxyl adversely affected root colonization by G. mosseae and decreased rhizosphere activity as measured by esterase activity. Chemical names used: N-(2-methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate) (metalaxyl); propyl 3(dimethylamino)propylcarbamate (propamocarb).

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Robert R. Tripepi and Mary W. George

De-inked paper sludge from a newsprint mill was evaluated as a substitute for sofwood bark in container media. Rooted cuttings of `Youngstown' juniper (Juniperus horizonatlis), Fraser photinia (Photinia × fraseri), and `PJM' rhododendron (Rhododendron) were planted in 3-L plastic pots that contained potting media amended with 0%, 20%, 40%, 60%, 80%, or 90% paper sludge and 80%, 60%, 40%, 20%, or 0%, respectively, bark (by volume). All mixes contained 10% sand and 10% peatmoss except for the 90% mix, which lacked peatmoss. After 19 weeks, plant heights were measured for photinia and rhododendron, but average plant width was measured for juniper. Shoot dry weights were also determined for all species. Juniper and photinia seemed to be the most tolerant of media amended with up to 40% paper sludge, whereas rhododendron was the most intolerant species. Shoot dry weights of juniper or photinia were similar for plants grown in media containing 40% or less paper sludge. Shoot dry weights of rhododendron plants grown in 40% sludge were 23% lower than those grown in 0% or 20% paper sludge, which were similar to each other. Plant heights followed similar trends to those of the shoot dry weights. With the exception of juniper, shoot dry weights and heights were drastically reduced if the potting mixes contained more than 40% paper sludge. These results demonstrated that de-inked paper sludge could be substituted for up to 40% of the bark in a container medium for two of the three species tested.

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Alicia Sanchez-Escarcega and George C. Elliott

The potential for N mineralization or immobilization in potting media containing compost was investigated in experiments using sunflower (Helianthus annuus `Sunrich Yellow') as a test crop with potting media formulated from 3 aged pine bark: 2 sphagnum peat or compost: 1 vermiculite (by volume). Cropped and uncropped media in 350-mL pots were fertilized by subirrigation with complete nutrient solutions containing N at 2, 4, 6, 8 or 12 mmol·L–1 as ammonium nitrate. In control medium without compost, sunflower fresh mass increased linearly with increasing N. In one compost medium (C), growth was stimulated and with N at 6 mmol·L–1 was equal to growth with N at 12 mmol·L–1 in the control medium. With another compost medium (A), growth was inhibited and did not respond to increasing N. In medium C, saturated media extracts (SME) obtained before and up to 12 days after transplanting had higher concentrations of NH4 and NO3 than the control medium. In medium A, NH4 concentrations were similar to controls, but NO3 concentrations were lower. Nitrite concentrations were less than 0.2 mmol·L–1 and were highest in medium C. Nitrogen derived from compost in medium C substantially reduced the soluble fertilizer N requirement for sunflowers, while N immobilization by compost in medium A was not overcome by increasing fertilizer N.

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Yin-Tung Wang and Lori L. Gregg

The levels of hydration of several hydrophilic polymers (hydrogels) varied greatly. Starch-based polymers had the fastest rate of hydration (<2 hours), followed by a propenoate-propenamide copolymer. Polyacrylamide materials required 4 to 8 hours to become fully hydrated. Maximum water retention in distilled water varied from 400 to 57 g of water per gram of dry material. All hydrogels retained less water in the presence of metal ions or fertilizers in the soaking solution, with substances releasing Fe+2 being the most detrimental. After exposure to fertilizers and ions, the water-holding capacity of a polyacrylamide with a high degree of cross linkage, but not that of hydrogels of the other structures, was fully recovered by subsequently soaking in distilled water. Pots amended with a polyacrylamide polymer but without Micromax (a micronutrient source) reached maximum water retention after six irrigations, while those with Micromax required 10 irrigations to reach peak water retention. The amounts of water being held in pots decreased after repeated fertilization. Medium volume increased with increasing levels of the polyacrylamide Supersorb C (0, 2, 4, or 6 g/pot). Micromax incorporated in medium amended with Supersorb C caused a depression in volume. Medium bulk density, total water retention, and water retention per unit volume of medium were increased by the incorporation of the hydrogel, regardless of the presence of Micromax. Noncapillary porosity measured at container capacity in medium amended with Micromax progressively decreased as the amount of hydrogel increased, but remained unchanged in medium without Micromax. Repeated drying and dehydration of the medium resulted in reduced water retention and increased noncapillary pore space.

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J.A.S. Grossi, H.B. Pemberton, and H.J. Lang

Plants of Rosa L. `RUIjef', `RUIdodo', and RUIrosora' were grown using a short-cycle production schedule. Rooted cuttings were established in 11.4-cm pots followed by pinching to start a final forcing period. Paclobutrazol was sprayed at 0, 25, 50, 100, or 200 mg·L-1 when shoots growing after the pinch were 2 to 3 cm long. Plants were harvested when at least two flowers were at stage 2 (showing color, calyx reflexing, no petals reflexed). At harvest, plants were moved to a simulated interior environment at 21 °C with 30 lower case μmol·m-2·s-1 fluorescent light. Plants of `RUIjef' had the most flowers per pot, whereas plants of `RUIdodo' were the shortest and the latest to flower. Plants of `RUIrosora' exhibited the longest shelf-life, but cultivars responded similarly to paclobutrazol treatments. Paclobutrazol treatment at 50 mg·L-1 and above resulted in shorter plants than the control while 25 mg·L-1 and above reduced peduncle length. Days to harvest was unaffected. Plant shelf-life was reduced 2.1 d by 100 or 200 mg·L-1 paclobutrazol treatment in comparison to the control. Longevity of selected individual flowers was reduced 1.4 d after 50 mg·L-1 treatment and by 2.2 d after 100 mg·L-1 treatment. Leaf abscission during the interior evaluation period was significantly reduced by paclobutrazol treatment of 50 mg·L-1 or higher, but leaf abscission overall was less than 10%. Considerations of height control, plant shelf-life and floral longevity should be balanced when using paclobutrazol in miniature pot rose production.

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D.G. Ranamukhaarachchi, R.J. Henny, C.L. Guy, and Q.B. Li

Randomly amplified polymorphic DNA (RAPD) markers were utilized to determine the genetic relationships of nine morphologically similar pot plant cultivars of Anthurium sp. by developing DNA fingerprints (DFP). Of 25 arbitrary primers screened, nine generated DFPs that were used in computing the genetic distance (d) and similarity coefficient (C) values. All cultivars tested exhibited a high degree of genetic similarity. `Lady Ann' and `Lady Beth' possessed the closest relationship with d and C values of 0.06 and 0.98, respectively. The next closest genetic relationship was between `Red Hot' and `Southern Blush' (d = 0.33, C = 0.89). These two cultivars exhibited a more distant relationship to the other seven cultivars as indicated by higher `d' values. However, this study showed that the nine Anthurium cultivars examined were genetically closely related. These cultivars share specific DNA bands with three possible parental species (A. andraeanum Linden ex Andre, A. antioquens L., and A. amnicola Dressler) included in this study, which may indicate similarities in their pedigree. This study shows that RAPDs can be a useful tool to distinguish Anthurium pot plant cultivars as well as identify their genetic relationships.

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Harvey J. Lang and George C. Elliott

Effects of medium, NH4: N03, ratio, and N fertilizer rate on the development of NH4 oxidation in soilless potting media were evaluated. In two separate experiments, NH4 oxidizing activity increased to a maximum (4 to 6 weeks of cropping) and then dropped off sharply. Ammonium oxidation activity varied significantly among types of soilless potting media. Media fertilized with 1 NH4-N: 3 N03-N had higher rates of NH4 oxidation than media fertilized with ratios of either 1:1 or 3:1. Nitrogen fertilization at 15 mm gave consistently higher oxidation rates than fertilization at 30 mm. In general, media samples that had been cropped with plants had higher nitrifying activity than unplanted samples. Ammonium oxidation rate over all observations was significantly correlated with medium pH (r = 0.50). pH values above 6.8 were necessary but not completely sufficient for relatively high rates of NH4 oxidation. Rates of oxidation were insignificant with pH values <5.6.

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Mark H. Brand

Potting of bare-root spring divisions is a simplified approach to ornamental grass production. Large and small divisions of eight common ornamental grasses were directly potted into 7-L nursery containers and grown outdoors for 20 weeks to determine an appropriate division size for each grass. Response to division size was dependent on the grass species. Large divisions of Calamagrostis ×cutiflora `Karl Foerster' (Schräd.) produced twice as many inflorescences as small divisions. At harvest, large divisions of Miscanthus oligostachyus `Purpurascens' (Stapf.) had twice as many inflorescences and 1.5 times as many tillers as small divisions. However, new tiller production in large divisions was only 50% of that in small division plants. Large divisions of Miscanthus sinensis (Anderss.) cultivars produced more tillers and greater fresh and dry weights than did small divisions, but again, the differences were not proportional to the size difference between the initial divisions. Large divisions of Panicum virgatum (L.) produced 50 more tillers per plant than did small divisions, but plant weight, size, and number of inflorescences were not affected by division size. Plants from large divisions of Pennisetum alopecuroides (L.) Spreng. were 7 cm shorter than small divisions and produced 24% more inflorescences and 27% more tillers, but appeared nutrient and/or water stressed. For most grasses, smaller division size is recommended for direct spring potting.

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R. Dudley Williams and Nancy A. Reichert

Two types of ground kenaf core (fresh and aged) were used in concentrations from 70% to 100% (v/v) in combination with peat for use as greenhouse potting media and were compared to two commercial mixes in completely randomized block designs. Greenhouse crops of Boston fern (Nephrolepis), impatiens, and pansies (Viola) were grown in the different mixes. Irrigation was conducted regularly, based primarily on the average need of all the plants. Kenaf-based media did not retain water as well as the commercial mixes. Consequently, impatiens and pansies displayed slower growth rates. However, no differences were noted for fern growth in 70% kenaf compared to commercial mixes. A second study on plants that were grouped by media type and watered as needed provided different results. Ferns grew equally well in all media, but impatiens grew best in 70% fresh kenaf. Kenaf-based media were less costly than the commercial mixes, and the cost decreased steadily as the kenaf proportion increased. The lower cost of kenaf coupled with the decreasing availability of peat should make kenaf-based media an attractive alternative to conventional greenhouse potting media.