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In commercial greenhouses, fan flower ‘Whirlwind Blue’ (Scaevola aemula R. Br.) plants are sensitive to phosphorus applications in the range typically applied to other floricultural crops. To quantify this response, fan flower plants were grown in Hoagland solutions containing 0, 20, 40, 60, or 80 mg·L−1 P. Plants fertilized with either the highest (80 mg·L−1) or lowest (0 mg·L−1) P concentrations had significantly shorter stems and smaller shoot dry weights and leaf areas than plants fertilized with 20 to 60 mg·L−1 P. Low or high P concentrations negatively impacted flower number; fan flower fertilized with 0, 60, or 80 mg·L−1 P had fewer flowering branches and flowers compared with plants fertilized with 20 to 40 mg·L−1 P. Plants receiving no P had longer roots than those receiving any P and had greater root dry weights than plants receiving all other P concentrations except 20 mg·L−1. Foliar nutrient analysis indicated that although P treatments significantly impacted foliar concentrations of at least some essential macro- and micronutrients, all essential elements were within or near recommended ranges except P. Foliar P concentrations exceeded 1 mg·g−1 in fan flower that received even the lowest concentration of supplemental P, but leaf chlorosis was only observed in plants grown in 60 to 80 mg·L−1 P. As a result of rapid accumulation of P in fan flower foliage and subsequent reductions in flower number and shoot elongation, fan flower should be fertilized with no more than 20 mg·L−1 P.

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Due to uncertainties of future supplies of pine bark (PB) and peatmoss, ground Pinus taeda logs [pine chips (PC)] were compared to ground PB as a potential container substrate for japanese holly (Ilex crenata Thunb. `Chesapeake'), azalea (Rhododendron obtusum Planch. `Karen'), and marigold (Tagetes erecta Big. `Inca Gold'). Plants were potted in 2.8-L plastic containers 8 Apr. 2004 with either 100% PC, 100% PB, or 75% PC:25%PB (v/v), and glasshouse grown 8 weeks for marigold and 13 weeks for holly and azalea. Plant dry weights were higher for marigold grown in 100% PB compared to 100% PC but not different from plants grown in 75% PC:25% PB. Plant dry weights of azalea were higher in 100% pine bark than both substrates containing chips. There was no difference in shoot dry weight for japanese holly between the three substrates. Root dry weight was higher for 75% PC:25% PB than for 100% PB, but root weight of 100% PB and 100% PC was the same. The percent air space for the PC was higher than the PB substrate but container capacity and available water was not different for the three substrates. Substrate solution electrical conductivity (EC) for PC, was lower than that of PB, possibly due to greater leaching with the more porous PC and nutrient retention by the PC. These factors could account for the cases where larger plants developed with the PB substrate. Nutrient analysis of the substrate solution indicated that there are no toxic nutrient levels associated with PC. The pH of PC is also acceptable for plant culture. As well, there was no apparent shrinkage due to decomposition during the course of this short-term experiment. Pine chips, therefore, offer potential as a container substrate for greenhouse and nursery crops.

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Abstract

The relative P dependency obtained for 3 citrus rootstock cultivars was rough lemon [Citrus limon (L)] > Carrizo citrange [Poncirus trifoliate × C. sinensis (L.)] > trifoliate orange [P. trifoliate (L.)]. After only 12 weeks of P deprivation, the youngest, fully expanded leaves of rough lemon (about 21 days old) had amounts of total N, nitrate, and NH3 that exceeded the levels in +P leaves of the same age by 8.4 mg total N, 2.6 mg nitrate, and 0.6 mg NH3 per gram of dry weight. It took 7 months for similar levels of these compounds to accumulate in the youngest, fully expanded leaves of Carrizo citrange (a less P-dependent rootstock) when grown under low P conditions. After 12 weeks of P deficiency, the incorporation of NaH14CO3 into arginine plus urea was 13-, 7.4-, and 4.7-fold greater in P-deficient leaves than P-sufficient leaves for rough lemon, Carrizo citrange, and trifoliate orange, respectively. Concomitantly, arginine accumulated in — P leaves to a concentration 4.2-, 2.1-, and 1.4-fold greater than in +P leaves, respectively, for the same 3 rootstocks. The data clearly demonstrate that relative P dependency of citrus rootstocks influences their N metabolism and support the hypothesis that a more P-dependent rootstock will accumulate total N, nitrate, and NH3 sooner or to a greater extent, exhibit a greater rate of de novo arginine biosynthesis, and accumulate a higher level of arginine than a less P-dependent rootstock. Thus, calculation of the N:P ratio during leaf nutrient analysis may be useful in evaluating the nutritional status of citrus trees. Whenever N:P ratios were >20, de novo arginine biosynthesis and arginine accumulation increased significantly, indicative of ammonia detoxification. The N:P ratio of P-sufficient plants was always <15 when arginine metabolism was normal.

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The objective of this study was to evaluate the potential use of container substrates composed of whole pine trees. Three species [loblolly pine (Pinus taeda), slash pine (Pinus elliottii) and longleaf pine (Pinus palustris)] of 8–10 year old pine trees were harvested at ground level and the entire tree was chipped with a tree chipper. The chips from each tree species were then further processed with a hammer mill to pass a ½-inch screen. On 29 June 2005 these three substrates along with 100% pinebark were mixed with the addition per cubic yard of 9.49 kg·m–3 Polyon 18–6–12 (18N–2.6P–10K), 2.97 kg·m–3 dolomitic lime and 0.89 kg·m–3 Micromax. One gallon (3.8 L) containers were then filled and placed into full sun under overhead irrigation. Into these containers were planted 72 cell plugs of Catharanthus roseus`Little Blanche'. Data collected were pre-plant chemical and physical properties of substrates, as well as plant growth index (GI), plant top dry weight, root ratings, and plant tissue (leaves) nutrient analysis at 60 days after planting (DAP). The test was repeated on 27 Aug. 2005 with C. roseus Raspberry Red Cooler. Top dry weights were on average 15% greater for the 100% pinebark substrate over all others at 60 DAP. However there were non differences in plant GI for any substrate at 60 DAP. There were no differences in plant tissue macro nutrient content for any substrate. Tissue micronutrient content was similar and within ranges reported by Mills and Jones (1996, Plant Analysis Handbook II) with the exception of Manganese. Manganese was highest for slash and loblolly pine and well over reported ranges. There were no differences in root ratings. There were no differences in substrate physical properties between the three whole tree substrates. However the 100% pinebark substrate had on average 50% less air space and 25% greater water holding capacity than the other substrates. Physical properties of all substrates were within recommended ranges. Based on the results of this study substrates composed of whole pine trees have potential as an alternative sustainable source for a substrate used in producing short term nursery crops.

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In current horticultural practice, potential acidity or basicity of fertilizers is estimated using Pierre's method (PM) expressed in calcium carbonate equivalents (CCE) per unit weight of fertilizer. PM was developed using mineral field soil systems and may be inaccurate for quantifying fertilizer acidity in containerized plant production given the widespread use of soilless substrates and fertigation. The PM-predicted acidity of an ammonium-based fertilizer was compared against experimental data obtained when ‘Ringo’ geraniums [Pelargonium ×hortorum (Bailey. L.H.)] and ‘Super Elfin’ impatiens [Impatiens wallerana (Hook. F.)] were grown in 70% peat:30% perlite (v:v) limed with either hydrated limestone only (HL) or a combination of carbonate and hydrated limestone (CHL). Plants in 10-cm-diameter (0.35 L) containers were top-irrigated with a total of 2.0 L over 6 weeks using a 15.2N–1.9P–12.6K fertilizer [100% of nitrogen (N) as NH4-N] applied with each irrigation at 100 mg N/L without leaching. According to PM, 61.8 meq of fertilizer acidity was applied per liter of substrate. During the experiment, the pH of the substrate decreased from 7.05 to 4.41 for the HL substrate and from 7.14 to 5.13 for the CHL substrate. A corresponding drop in substrate-pH was observed when 37.1 (HL) or 43.3 (CHL) meq of CCE from 0.5 N HCl was applied per liter of substrate in a laboratory titration of the same substrates without plants. Gasometric analysis of residual carbonate at Day 0 and at the end of the experiment quantified change in CHL substrate alkalinity with time, resulting in an estimated 30.7 meq of neutralized alkalinity. Using an electroneutrality approach that assumed anion uptake (NO3 , P2O5 ) was basic, and cations (NH4 +, K+) were potentially acidic, nutrient analysis of the substrate at the beginning and end of the experiment estimated that an average 48.5 meq of acidity was contributed by the fertilizer. Experimentally measured acidity values were 13.1 to 31.1 meq·L−1 of substrate lower for HL and CHL than those expected from PM, suggesting PM overestimated the amount of fertilizer acidity applied to the substrate. These results support the need for an alternative method to predict fertilizer acidity for plant production in soilless substrates.

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For optimum plant growth in containers, adequate plant nutrition is essential. Objectives of this research were to determine the optimum fertilization of tomatoes (Lycopersicon esculentum Mill.) in a peatbased medium and to assess plant nutrition by plant and media analysis. Tomato seedlings ('Heinz 1437') were transplanted (one plant per pot) into 2-L pots filled with a peat-based medium. The medium was fertilized with a progressive array of soluble fertilizers to supply N at 0, 50, 100, 150, or 200 mg·L-1 of solution with concomitant proportional increases of other macronutrients with each increase in N (P at 0, 10, 20, 30, or 40; K at 0, 40, 80, 120, or 160; Ca at 0, 50, 100, 150, or 200; and Mg at 0, 12, 24, 36, or 48 mg·L-1). The plants were irrigated starting with 100 mL fertilizer solution per day and increasing to 200 mL per day as plant growth progressed. The tomatoes were harvested at three stages of growth (five-leaf stage, flower initiation, and fruit initiation) for analysis of growth and composition. Samples of media for nutrient analysis were taken at each growth stage. Plant biomass increased linearly as fertilizer level increased or as time progressed. Generally, concentrations of nutrients in the medium increased linearly with increases in nutrients in the solutions. With time, N concentrations in media rose, but P, K, Ca, and Mg in the media fell. Concentrations of N, P, or K in leaves increased as nutrition increased, but Mg or Ca in leaves had no significant changes with increased nutrient supply. The N, P, Ca, and Mg in tissues fell, but K rose with time. Assessment of plant nutrition was best at flower initiation, with assessments at the other stages of development being judged as untimely or excessively variable. For optimum growth, critical concentrations of nutrients in the media (mg·kg-1) at flower initiation were judged to be 30 NO3-N, 30 P, 300 K, 2600 Ca, and 800 Mg and in leaves (g·kg-1) to be 35 N, 10 P, 70 K, 35 Ca, and 20 Mg. Optimum fertilization to reach these critical concentrations was reached with the third level (the regime with 100 mg N/L) or higher levels of nutrition.

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calyx of the uppermost flower. The number of flowers per plant included senesced flowers and buds displaying flower color. A tissue nutrient analysis was performed for the entire aboveground shoot, including the leaf, stem, and flowers, of plants

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fruitlets ( N = 5), dried, and then ground using a mortar and pestle for nutrient analysis. Calcium chloride preparation, isotope application. The 44 CaCl 2 (calcium chloride) solution was prepared by weighing 200 mg of 97 atom% CaCO 3 (Cambridge Isotope

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plant into the leaf, stem, and root at the end of experiment (day 30). Plant biomass was not measured on day 0 because biomass measurement would have required destruction of the trees. Growing media and mineral nutrient analysis. The pH of the

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were repeated with the same procedures described above with only anise and muhly grass, and with the omission of leaf tissue nutrient analysis. Sweetspire was omitted based on its lack of tolerance to NaCl concentrations applied in the first run; the

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