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Raul I. Cabrera and Diana Devereaux

Ilex opaca and Lagerstroemia indica plants were grown over 9 months using complete nutrient solutions differing in N concentration [(N)A: 15, 30, 60, 120, 210 and 300 mg·L–1]. Biomass production increased as (N)A were raised from 15 to 60 mg·L–1, but was depressed by higher concentrations. Increases in (N)A produced higher shoot: root ratios. Maximum leaf N concentration was observed at 60 mg·L–1, with similar values at higher (N)A. Plant survival, establishment and performance was evaluated over 15 weeks following transplant (15 WAT) to a landscape with minimum management conditions. Despite the initial significant differences in growth, shoot: root ratios and plant N status, plant establishment was not affected following transplant. Plant characteristics changed significantly over time, and by 15 WAT, all of the measured variables were statistically the same across all treatments. Flowering was, however, delayed over several weeks for Lagerstroemia indica plants grown at the higher (N)A. Analysis of these results indicate that plant production under relatively low N levels in the nursery maximizes N fertilizer use efficiency without affecting landscape establishment and performance.

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Raul I. Cabrera and Pedro Perdomo

Herbaceous perennials are the hottest item in the ornamental industry, yet relatively little is known about the most appropriate management and cultural practices for many of these species. The response of selected perennials to controlled-release fertilizer (CRF) rates was evaluated in this study. Liners of Coreopsis `Early Sunrise' and `Zagreb', Astilbe `Bridal veil', Hemerocallis `Stelladoro', Phlox `Franz Shubert', and Rudbeckia `Goldstrum' were transplanted to 5.7-L pots filled with a 2 peat: 1 perlite (v/v) medium amended with dolomite and Micromax (2 and 0.6 kg·m-3, respectively). Plants were topdressed with Osmocote 18N-2.7P-10K at rates of 0, 1.8, 3.6, 5.3, 7.1 (industry standard) and 8.9 kg·m-3, and grown over a 3-month period. Plant biomass and quality ratings (including chlorophyll levels) followed an asymptotic behavior with CRF applications for Coreosis `Early Sunrise' and Astilbe `Bridal veil', leveling at ≈1.8 kg·m-3. The rest of the species showed increases in plant growth and quality with CRF rates of 1.8-3.6 kg·m-3, followed by sharp, and significant, reductions at higher CRF rates. Observations of optimum growth and quality at CRF rates 1/2 to 3/4 below commercial recommendations were partially attributed to the use a peat medium, with relatively higher nutrient holding characteristics in relation to the more common pine bark mixes. This observation was confirmed the following season, where plants grown in a 4 pine bark: 1 sand medium (v/v) required higher CRF rates to have similar growth and quality responses to those grown in a 4 peat: 1 bark: 1 sand medium (v/v).

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Raul I. Cabrera and Diana R. Devereaux

Containerized crape myrtle (Lagerstroemia indica L. × Lagerstroemia fauriei Koehne `Tonto') plants were grown for 9 months under various nitrogen fertility regimes, and then transplanted to a sandy loam soil with minimal management to evaluate their landscape establishment and growth performance. During the nursery phase plants were irrigated, except over an overwintering period, with complete nutrient solutions differing in applied N concentration, ranging from 15 to 300 mg·L-1. By 16 weeks after transplanting (WAT) into the landscape soil, plant biomass was significantly higher in the plants that had been grown with higher N supplies and had been among the smallest at transplant. Such plant growth response was linearly and positively correlated to plant N status at transplant. Plant shoot to root ratio and tissue N, Ca, S, and Fe concentrations, which had been significantly affected by the N fertilization regime in the nursery, equalized over time after transplant, with no significant differences observed among treatments by 16 WAT. Flowering response in the landscape was delayed in plants originally grown with the higher N supplies. Plant survival and establishment per se were not affected by treatments; no plants were lost, and aside from the differences in size and flower timing, all plants were considered aesthetically similar.

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Alma R. Solis-Perez and Raul I. Cabrera

Greenhouse rose plants, `Bull's Eye', budded on the rootstocks Rosa manetti and R. × `Natal Briar', were grown in containers filled with a peat-based growing medium. The plants were irrigated with a 0.5× Hoagland solution salinized with a fixed 12-mM Na solution made up of seven ratios of NaCl, Na2SO4, and NaNO3 (100:0, 50:50:0, 0:100:0, 0:50:50, 0:0:100, 50:0:50, and 33:33:33). The results after four flushes of growth and flowering showed higher dry weight productivities in R. manetti plants. Salt composition (i.e., counter-anion ratios) significantly affected the dry weight yield of `Natal Briar' plants, with those irrigated with 100% Na2SO4 and NaNO3 having the highest and lowest values, respectively. While the plants budded on R. manetti did not show significant responses to salt composition, there was a strong tendency for higher dry weight yields in binary salt (anion) compositions. Leachates collected throughout the study showed similar pH (7.5) and electrical conductivities (4.7 dS/m) for all salt treatments. Leachate Cl- concentrations were linearly correlated with Cl- application, whereas leachate Na+ concentrations remained similar among treatments. Plants on R. manetti accumulated less leaf Na+ and Cl- than in R. × `Natal Briar' plants, with lower values observed, in general, in plants irrigated with solutions containing Na2SO4.

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Raul I. Cabrera and Richard Y. Evans

The establishment of critical tissue N (Ncrit) for greenhouse rose production has been primarily based on visual symptoms of N deficiency, with relatively less consideration to yield parameters. This work examined the relationship between rose leaf N concentration and flower yield and quality. Microlysimeter-grown `Royalty' rose plants were irrigated with complete nutrient solutions containing N concentrations of 30, 60, 90, 120, 150, and 220 mg·liter–1. Results after 1 year indicated no significant differences in total dry weight, number of flowers, and stem length for plants irrigated with 90 to 220 mg·liter–1 N. Tissue N concentrations were significantly lower for plants that received 30 or 60 mg N/liter. Estimated Ncrit for yield parameters were ≈2.7% of leaf dry weight. Chlorophyll content and color leaf attributes (hue, chroma, and value) were correlated with tissue N concentration. The results suggest that the rate of N application typically recommended for greenhouse roses is considerably higher than necessary.

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Raul I. Cabrera, Richard Y. Evans, and J. L. Paul

N deprivation is known to increase the rate of N uptake by graminaceous plants, but such response has not been reported for mature woody plants. A recirculating nutrient solution system was utilized to study the effect of intermittent N-deprivation on N uptake by mature `Royalty' rose plants. Plants received a nutrient solution lacking N for 4, 8 or 16 days, after which one containing N was supplied for 4 days. N-deprivation resulted in a 2-3 fold increase in N uptake rate compared to control plants supplied continuously with N (e.g., 143 vs 62 mg N plant-1 day-t). The magnitude of this deprivation-enhanced N uptake was not affected by either the duration of N-deprivation or the plant developmental stage.

A characteristic diurnal pattern of N uptake was observed in both N-starved and control plants. Uptake oscillated between minimum rates in the morning and maximum rates in the evening, the latter occurring 4-6 hr after the maximum transpiration rates.

The ability to increase the rate of N uptake in roses by depriving them of N for several days may be of practical importance for increasing N fertilizer use efficiency and decreasing N losses to leaching.

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Raul I. Cabrera, James A. Reinert, and Cynthia B. McKenney

Field (choice) and laboratory (no choice) studies were conducted to evaluate the susceptibility of 12 crape myrtle (Lagerstroemia) cultivars, representing two species and their interspecific hybrids, to feeding damage by the flea beetle (Altica litigata Fall). The results indicate that as a group, the L. indica L. cultivars were more susceptible to attack and significant herbivory damage by Altica beetles, whereas all the L. fauriei Koehne cultivars and most of the interspecific L. indica × fauriei hybrids were resistant. Significant differences in feeding damage were observed between the new and older leaves in the susceptible hybrid ‘Biloxi’ and L. indica ‘Whit IV’, but not in the rest of the cultivars. Mineral nutrient content differences were observed between species with L. indica cultivars having a significantly contrasting nutrient status profile compared with the L. fauriei and interspecific hybrid cultivar groups. The results indicate that the factors influencing Altica flea beetle-feeding preferences and damage are inherited and therefore will allow the implementation of pest management practices that minimize damage and optimize chemical control strategies. In addition, opportunities may exist for breeding and selection efforts that could lead to superior cultivars with insect resistance.

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Raul I. Cabrera, James E. Altland, and Genhua Niu

Scarcity and competition for good quality and potable water resources are limiting their use for urban landscape irrigation, with several nontraditional sources being potentially available for these activities. Some of these alternative sources include rainwater, stormwater, brackish aquifer water, municipal reclaimed water (MRW), air-conditioning (A/C) condensates, and residential graywater. Knowledge on their inherent chemical profile and properties, and associated regional and temporal variability, is needed to assess their irrigation quality and potential short- and long-term effects on landscape plants and soils and to implement best management practices that successfully deal with their quality issues. The primary challenges with the use of these sources are largely associated with high concentrations of total salts and undesirable specific ions [sodium (Na), chloride (Cl), boron (B), and bicarbonate (HCO3 ) alkalinity]. Although the impact of these alternative water sources has been largely devoted to human health, plant growth and aesthetic quality, and soil physicochemical properties, there is emergent interest in evaluating their effects on soil biological properties and in natural ecosystems neighboring the urban areas where they are applied.

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Raul I. Cabrera, Richard Y. Evans, and J. L. Paul

Nitrogen leaching losses of 21, 40 and 49% were measured from container-grown `Royalty' roses irrigated for one year with nutrient solutions containing 77, 154 and 231 mg N/l. There were no significant differences in number of flowers per plant or dry matter per plant. The N present in the harvested flowers accounted for 43, 27 and 17% of the N applied for the 77, 154 and 231 mg N/l treatments, respectively.

Plants receiving 154 mg N/l at leaching fractions of 0.1, 0.25 and 0.5 had corresponding N leaching losses of 22, 38 and 56%. In this experiment, however, the 0.5 leaching fraction produced yields significantly higher than those of the 0.1 and 0.25 treatments. The N recovered in the harvested flowers accounted for 28, 25 and 19% of that applied to the 0.1, 0.25 and 0.5 treatments, respectively.

The results of these studies suggest that modifications in current irrigation and fertilization practices of greenhouse roses would result in a considerable reduction of N leaching losses and enhance N fertilizer use efficiency, without loss of cut flower yield and quality.

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Raul I. Cabrera, Richard Y. Evans, and J.L. Paul

N uptake by greenhouse roses is out of phase with flower shoot elongation, such that N uptake is highest when shoots are not growing and lowest when shoots are elongating rapidly. Isotopically labelled 15N fertilizer was supplied at different stages of one flowering cycle to `Royalty' rose plants growing in a static nutrient solution system to study the partitioning of recently-absorbed N and the dynamics of N partitioning. After a two-day exposure, whole plants were harvested, separated into old and new leaves, stems, and roots, and analyzed for total N and 15N enrichment. During rapid shoot elongation, N uptake by roots supplied 16 to 36% of shoot N demand. The remaining N came from other organs, particularly old stems and leaves. The increased N uptake later in the flowering cycle was sufficient to meet shoot N demand and replenish the N supply in old foliage and woody tissues. These organs continued to accumulate N until the subsequent bud break, when this N became available for the next cycle of flowering shoot growth.