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Timothy K. Broschat

Royal palms [Roystonea regia (HBK.) O.F. Cook], coconut palms (Cocos nucifera L. `Malayan Dwarf'), queen palms [Syagrus romanzoffiana (Chamisso) Glassman], and pygmy date palms (Phoenix roebelenii O'Brien) were grown in a rhizotron to determine the patterns of root and shoot growth over a 2-year period. Roots and shoots of all four species of palms grew throughout the year, but both root and shoot growth rates were positively correlated with air and soil temperature for all but the pygmy date palms. Growth of primary roots in all four species was finite for these juvenile palms and lasted for only 5 weeks in royal palms, but ≈7 weeks in the other three species. Elongation of secondary roots lasted for only 9 weeks for coconut palms and less than half of that time for the other three species. Primary root growth rate varied from 16 mm·week-1 for coconut and pygmy date palms to 31 mm·week-1 for royal palms, while secondary root growth rates were close to 10 mm·week-1 for all species. About 25% of the total number of primary roots in these palms grew in contact with the rhizotron window, allowing the prediction of the total root number and length from the sample of roots visible in the rhizotron. Results indicated that there is no obvious season when palms should not be transplanted in southern Florida because of root inactivity.

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Timothy K. Broschat

Mature pygmy date palms (Phoenix roebelenii O'Brien) having a minimum of 90 cm of clear trunk were transplanted into a field nursery at their original depth or with 15, 30, 60, or 90 cm of soil above the original rootball. Palms planted at the original level or with the visible portion of the root initiation zone buried had the largest canopies, highest survival rates, and lowest incidence of Mn deficiency 15 months after transplanting. Palms planted 90 cm deep had only a 40% survival rate, with small, Mn-deficient canopies on surviving palms. Palms whose original rootballs were planted 90 cm deep had very poor or no root growth at any level, but had elevated Fe levels in the foliage. None of the deeply planted palms produced any new adventitious roots higher than 15 cm above the visible portion of the root initiation zone.

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Timothy K. Broschat

Palms (Arecaceae) growing in containers have similar nutritional requirements as other tropical ornamental plants and grow well with fertilizers having an elemental ratio of 3N:0.4P:1.7K. However, palms growing in the landscape or field nurseries have very different nutritional requirements from dicotyledonous plants. Whereas nitrogen (N) is the primary limiting nutrient element in container production, potassium (K), manganese (Mn), magnesium (Mg), boron (B), and iron (Fe) deficiencies are more widespread than N deficiency in most landscape soils. Because palms have a single apical meristem, deficiencies of K, Mn, or B can be fatal. In addition to insufficient nutrients in the soil, palm nutrient deficiencies can be caused by high soil pH, certain types of organic matter, deep planting, poor soil aeration, cold soil temperatures, and nutrient imbalances. Correction of nutritional deficiencies in palms can take up to 2 years or longer and therefore prevention of deficiencies by proper fertilization is important. Research has shown that high N:K ratio fertilizers applied directly, or indirectly via application to adjacent turfgrass in a landscape, can exacerbate K and Mg deficiencies in palms, sometimes fatally. For sandy Atlantic coastal plain soils in the southeastern United States, an analysis of 8N–0.9P–10K–4Mg plus micronutrients has been recommended.

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Timothy K. Broschat

Release rates at 21 °C were determined in sand columns for 12 commercially available soluble and controlled-release Mg fertilizers. Lutz Mg spikes, K2SO4, MgSO4, MgSO4·H2O, and MgSO4·7H2O released their Mg within 2 to 3 weeks. Within the first 6 weeks, MgO·MgSO4 released its soluble Mg fraction, but little release occurred thereafter. Dolomite and MgO released <5% of their Mg over 2 years while MagAmp released <20% of its Mg. Florikan 1N-0P-26K-4Mg types 100 and 180 exhibited typical controlled-release fertilizer characteristics, with most of their Mg release occurring during the first 15 weeks.

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Timothy K. Broschat

`Petite Yellow' dwarf ixoras (Ixora spp.) were grown in an alkaline substrate (3 limestone gravel: 2 coir dust) or a poorly aerated composted seaweed substrate to induce iron (Fe) chlorosis. Chlorotic plants were fertilized every 2 months with soil applications of 0.1 g (0.0035 oz) Fe per 2.4-L (0.63-gal) pot using ferrous sulfate, ferric diethylenetriaminepentaacetic acid (FeDTPA), ferric ethylenediaminedi-o-hydroxyphenylacetic acid (FeEDDHA), Hampshire Iron (FeHEDTA plus FeEDTA), ferric citrate, iron glucoheptonate, or DisperSul Iron (sulfur plus ferrous sulfate). Additional chlorotic ixoras growing in a substrate of 3 sedge peat: 2 cypress sawdust: 1 sand were treated every 2 months with foliar sprays of Fe at 0.8 g·L-1 (0.11 oz/gal) from ferrous sulfate, FeDTPA, FeEDDHA, ferric citrate, or iron glucoheptonate. Only chelated Fe sources significantly improved ixora chlorosis when applied to the soil, regardless of whether the chlorosis was induced by an alkaline substrate or a poorly aerated one. As a foliar spray, only FeDTPA was effective in improving chlorosis in dwarf ixora. Leaf Fe content either showed no relationship to plant color or was negatively correlated with plant chlorosis ratings.

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Timothy K. Broschat

Four different organic mulches were applied to 1-m2 plots of Margate fine sand soil that were irrigated three times per week. A 8N–0.9P–10K–4Mg controlled-release fertilizer was applied above or below these mulches to determine the effects of fertilizer placement on weed growth and soil pH, nitrate–nitrogen, ammonium–nitrogen, potassium (K), and magnesium (Mg) concentrations. Unfertilized plots were used to determine mulch effects on soil pH and nutrient content. Fertilizer placement generally had no effect on any of these soil fertility parameters nor did it affect weed numbers. Cypress mulch increased soil K concentrations, and pine bark and eucalyptus mulch increased soil Mg over that of unmulched plots when no fertilizer was applied. The presence of any mulch type greatly reduced weed numbers over that of unmulched plots.

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Timothy K. Broschat

Five species of tropical ornamental plants—artillery fern (Pilea serpyllacea), pleomele (Dracaena reflexa), fishtail palm (Caryota mitis), areca palm (Dypsis lutescens), and sunshine palm (Veitchia mcdanielsii)—were grown in containers under full sun, 55% shade, or 73% shade. They were fertilized every 6 months with Osmocote Plus 15-9-12 (15N-4P-10K) at rates of 3, 6, 12, 18, 24, 30, and 36 g/pot (0.1, 0.2, 0.4, 0.6, 0.8, 1.1, and 1.3 oz/pot). For pleomele and the three palm species, optimum shoot dry weights and color ratings were similar among the three light intensities tested. However, artillery fern grown in full sun required fertilizer rates at least 50% higher for optimum shoot dry weight and color than under 55% or 73% shade. Light intensit × fertilizer rate interactions were highly significant for pilea and fishtail palm color and dry weight and sunshine palm and pleomele color.

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Timothy K. Broschat

Release rates for 13 commercially available soluble and controlled-release K fertilizers were determined in sand columns at 21C. Potassium chloride, KMgSO4, and K2CO3 were leached completely from the columns within 3 or 4 weeks. Osmocote 0N-0P-38.3K, Multicote 9N-0P-26.7K, the two S-coated K2SO4 products, and Nutricote 2N-0P-30.8K Ty 180 all had similar release curves, with fairly rapid release during the first 20 to 24 weeks, slower release for the next 10 to 12 weeks, and virtually no K release thereafter.

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Timothy K. Broschat

Coconut palms (Cocos nucifera) in a field planting that were fertilized with a 8N–0.9P–10K–4Mg fertilizer four times per year or were never fertilized experienced chilling injury (CI) temperatures in 2008, 2009, and 2010. Fertilized coconut palms had significantly less foliar necrosis in each year than unfertilized palms and also retained more of their fruits. The number of leaves supported by each palm, a measure of potassium (K) deficiency severity, was improved by fertilization and was negatively correlated with percentage of necrosis of the foliage caused by cold temperatures. Nitrogen and K concentrations in leaf 1 of coconut palms were also negatively correlated with CI severity.

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Timothy K. Broschat

Chinese hibiscus (Hibiscus rosa-chinensis), shooting star (Pseuderanthemum laxiflorum), downy jasmine (Jasminum multiflorum), areca palm (Dypsis lutescens), and `Jetty' spathiphyllum (Spathiphyllum) were grown in containers using Osmocote Plus 15-9-12 (15N-3.9P-10K), which provided phosphorus (two experiments), or resin-coated urea plus sulfur-coated potassium sulfate, which provided no phosphorus (one experiment). Plants were treated with water drenches (controls), drenches with metalaxyl fungicide only, drenches with phosphoric acid (PO4-P), drenches with metalaxyl plus phosphorus from phosphoric acid, drenches with PhytoFos 4-28-10 [4N-12.2P-8.3K, a fertilizer containing phosphorous acid (PO3-P), a known fungicidal compound], or a foliar spray with PhytoFos 4-28-10. Plants receiving soil drenches with equivalent amounts of P from PhytoFos 4-28-10, PO4-P, or PO4-P+metalaxyl generally had the greatest shoot and root dry weights and foliar PO4-P concentrations. There were no differences between the control and metalaxyl-treated plants, indicating that root rot diseases were not a factor. Therefore, responses from PhytoFos 4-28-10 were believed to be due to its nutrient content, rather than its fungicidal properties. Foliar-applied PhytoFos 4-29-10 produced plants that were generally similar in size to control plants or those receiving metalaxyl only drenches. Fertilizers containing PO3-P appear to be about as effective as PO4-P sources when applied to the soil, but are relatively ineffective as a P source when applied as a foliar spray. A distinct positive synergistic response for shoot and root dry weights and foliar PO4-P concentrations was observed for the PO4-P+metalaxyl treatment when no P was applied except as a treatment.