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Raul I. Cabrera*

The azalea hybrids `Delaware Valley White' (`DVW') and `Hershey Red' (`HR') were grown in 7-L containers filled with a 4 sphagnum peat: 2 pine bark: 1 sand medium (v/v) and fertigated for 15 weeks with a complete nutrient solution supplemented with 0, 6 and 12 mm NaCl-CaCl2 (2:1 molar ratio). Regardless of salinity stress, `DVW' plants had dry weights and leaf areas significantly higher (by 24.7% and 10.2%, respectively) than in `HR' plants. Salinity, however, caused differential growth and quality responses between the hybrids. Growth in `DVW' plants decreased with salinity increases, with 22.6% and 32.4% reductions in total dry weight and leaf area, respectively, observed at 12 mm salt compared to controls. Conversely, `HR' plants exposed to 12 mm salt showed no differences in yield parameters with respect to the controls, whereas plants receiving 6 mm salt showed increases of 14.0% and 7.1% in total dry weight and leaf area, respectively, with respect to the controls. Plant quality, as assessed by visual symptoms of salt injury (“salt burn”), was significantly reduced by salinity increases in `DVW' plants, but was not affected in `HR' plants. While unaffected by salinity, leaf K status in `HR' plants was significantly lower than in `DVW', which showed increases in K concentration with salinity increases. Leaf Ca, Cl and Na concentrations increased with added salinity in both hybrids. The `DVW' plants, however, accumulated exceedingly higher Cl and Na concentrations (up to 3.33% and 5,650 mg·L-1 respectively) than in `HR' plants (up to 1.31% and 463 mg·L-1, respectively). Only the yield and quality of `DVW' plants were negatively and significantly correlated to increases in leaf Cl and Na concentrations.

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Raul I. Cabrera

Yield, quality, and nutrient status of `Bridal Pink' (on R. manetti rootstock) roses were evaluated under increasing NaCl salinity and mixed NO3 /NH4 + nutrition. Container-grown plants were irrigated over eight flushes of growth and flowering with nutrient solutions having 100 NO3 - : 0 NH4 +, 75 NO3 : 25 NH4 +, and 50 NO3 : 50 NH4 + ratios in combination with three NaCl concentrations. During the first four flowering flushes, NaCl was supplemented at 0, 5, and 10 mm, but these concentrations were increased to 0, 15, and 30 mm during the last four flushes. Interestingly, NO3 : NH4 + ratios and NaCl concentration had no main effects over any flower yield or quality component evaluated over the 13-month experimental period. Furthermore, visual symptoms of apparent salt injury were just observed during the last three flowering cycles, and mostly on the oldest foliage of plants receiving the highest salt concentrations (30 mm). Leaf N and Na concentrations were not significantly affected by the treatments over the course of the experiment, averaging 3.34% and 45 mg·kg–1, respectively. Leaf Cl concentrations were significantly increased by salt additions, ranging from 1000 to 15,000 mg·kg–1 [0.1% to 1.5% dry weight (DW)]. Correlation analyses revealed that relative dry weight yields increased with leaf Cl concentrations up to 3000 mg·kg–1 (0.3% DW) but were significantly depressed at higher concentrations. These results confirm recent reports suggesting that roses are more tolerant to salinity than their typical classification of sensitive. Furthermore, this is the first known study to report an apparent positive effect of moderate leaf Cl concentrations on rose biomass yields.

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Raul I. Cabrera

Seven nursery grade (8- to 9-month duration), polymer-coated, controlled-release fertilizers (CRF) were topdressed or incorporated to a peat: sand: vermiculite medium to yield the same amount of N per container. The pots were uniformly irrigated with DI water every week. Leachates were collected and analyzed for N (ammonium plus nitrate) concentration. Two distinct N release (NR) patterns were observed over the 180-day experiment. Osmocote 18–6–12FS, Prokote-P 20–3–10, Osmocote 24–4–8HN, and Polyon 25–4–12 exhibited a NR pattern that closely followed changes in average daily ambient temperatures (AT) over the season. This relationship was curvilinear in nature, with NR being highly responsive to AT up to 25°C. Conversely, Osmocote 18–6–12, Nutricote 18–6–8 (270), and Woodace 20–4–12 showed a stable NR pattern over a wider range of AT, with NR rates 30% to 60% lower than those in the temperature-responsive CRF. Incorporation produced significantly higher cumulative N releases than topdressing but without effect on the actual pattern of NR over the season. Regardless of the N formulation in the CRF, >80% of the N recovered in the leachates was in the nitrate form.

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Raul I. Cabrera

Seven nursery grade (8-9 month duration), polymer-coated, controlled-release fertilizers (CRF) were topdressed or incorporated into a 2 peat: 1 vermiculite: 1 sand (by volume) medium to yield the same amount of N per container. The pots (0.5 L) were uniformly irrigated with DI water every week to produce a target leaching fraction of 25%. Leachate N contents (ammonium plus nitrate), employed as indicators of N release, allowed for comparison of CRF performance as a function of temperature changes over a season. Two distinct N leaching (i.e., release) patterns were observed over the 180-day experimental period. The fertilizers Osmocote 18-6-12FS (Fast Start: OSM-FS), Prokote Plus 20-3-10 (PROK), Osmocote 24-4-8HN (High N: OSM-HN) and Polyon 25-4-12 (POLY) exhibited a N leaching pattern that closely followed changes in average daily ambient temperatures (Tavg) over the season. This relationship was curvilinear, with N leaching rates per pot (NLR) being highly responsive to Tavg changes between 20 and 25 °C. Temperatures above 25 °C produced an average maximum NLR of 1.27 mg·d-1 for these fertilizers. OSM-FS, PROK, and OSM-HN had the highest cumulative N losses over the experimental period. In contrast, the CRF group formed by Nutricote 18-6-8 (270: NUTR), Woodace 20-4-12 (WDC), and Osmocote 18-6-12 (OSM) showed a more stable N leaching pattern over a wider range of temperatures, with rates about 30% to 40% lower than those in the temperature-responsive CRF, and averaging a maximum NLR of 0.79 mg·d-1 for Tavg >25 °C. NUTR and WDC had the lowest cumulative N losses over the season. Soluble salt readings paralleled N leaching for each CRF, indicating similar leaching patterns for other nutrients. Incorporation produced significantly higher cumulative N losses than topdressing, but without effect on the actual N leaching pattern over the season. Regardless of the N formulation in the CRF, over 85% of the N recovered in the leachates was in the nitrate form.

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Raul I. Cabrera

The establishment of critical tissue N levels 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. Container-grown `Royalty' rose plants were irrigated for 13 months with complete nutrient solutions containing N concentrations of 30, 60, 90, 120, 150 and 220 mg·L–1. Optimum flower and dry biomass yields, stem length, and stem weights were obtained in plants irrigated with 90 mg·L–1 N. Leaf N concentrations increased asymptotically with N applications, stabilizing at N concentrations >90 mg·L–1. Time of the year had an effect on overall leaf N concentrations, with higher values observed in the winter, and lower values in the summer. Leaf N concentrations were linearly, and significantly, correlated with leaf chlorophyll content and leaf color attributes (hue, chroma, and value). Quadratic relationships between leaf N concentration and rose plant yields were observed only for the second half of the experimental period, and depicted an apparent, and striking, plant control over tissue N status. In addition, these relationships indicated that optimum plant yields were possible during spring and summer with leaf N concentrations below the recommended critical level of 3% (as low as 2.4% to 2.5%). These results suggest that leaf N concentration per se is not a dependable indicator of rose productivity.

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Raul I. Cabrera*

Rooted liners of the crape myrtle cultivars `Pink Lace', `Natchez' and `Basham's Party Pink' (`BPP') were grown in 20-L containers filled with a 2 peat: 1 pine bark: 1 sand (v/v) medium and irrigated for 15 weeks with irrigation water containing 0, 3, 6, 12, and 24 mm NaCl. Cultivar selection and salinity significantly affected plant growth and quality. Regardless of salinity level, `Natchez' plants had higher leaf area, total and shoot (top) dry weights and growth indices, whereas `Pink Lace' had the lowest. `BPP' had the highest average root dry weights across salt treatments. The vigorous shoot (top) growth of `Natchez' was also evident with an average shoot to root ratio of 4.1, compared to 2.7 and 2.4 for `BPP' and Pink Lace', respectively. Salinity significantly decreased plant growth and quality in the three cultivars, but the rate at which these parameters were reduced with increases in salinity differed among the cultivars. The rate of reduction in plant growth parameters was lower in `Pink Lace' plants compared to `Natchez' and `BPP'. However, foliage burn symptoms due to salt stress increased at significantly higher rate for `Pink Lace' plants compared to the other two cultivars. `BPP' plants had in general the lowest salt burn ratings at each salinity level. Leaf concentrations of Na and Cl increased with salt stress in all cultivars, but significantly lower concentrations were found in `BPP' plants. `Pink Lace' plants had better correlations with the recorded salt burn symptoms as compared to the other two cultivars.

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Raul I. Cabrera and Pedro Perdomo

The performance of modern greenhouse-grown roses under intensive nutrient and water management practices questions their traditional classification as a salt-sensitive species, and emphasizes the need to reassess their salinity tolerance. Container-grown `Bridal Pink' roses (on R. manetti rootstock) in a peat moss-based growing medium were irrigated, using moderate leaching fractions (25% targeted, 37.5% actual), with complete nutrient solutions supplemented with NaCl at 0, 5, and 10 mm. These salt concentrations affected the electrical conductivity (EC) and Cl concentrations measured in the leachates, but had no significant effects on flower yield and quality over four growth and flowering flushes (§29 weeks). Cumulative yields over this period increased an average of §13% per leachate EC unit. Thereafter, the applied NaCl concentrations were increased 3-fold to 0, 15, and 30 mm and the plants continued to be evaluated for another four flowering flushes. No significant differences in cut-flower yield and quality were observed among salt treatments despite further increases in leachate EC and Na and Cl concentrations. Symptoms of salt injury were visually observed during the last three flowering cycles, and most heavily on the oldest foliage of plants receiving the highest salt concentration (30 mm), but not on the foliage of harvested shoots. The concentration of most nutrients in leaf tissue was not significantly affected by any of the treatments over the course of the experiment. Leaf Na concentrations were not affected by NaCl applications, averaging 42 mg·kg-1 across treatments. Conversely, leaf Cl concentrations increased significantly and cumulatively over time with salt additions, and ranged from 1.0 to 17.5 g·kg-1 (0.1 to 1.75%). Regression analyses revealed that average relative dry weight yields increased with leaf Cl concentrations up to 4.0 g·kg-1 (0.40%), but were depressed at higher concentrations.

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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 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

Hydrophilic polymer tubes (2.5 mm OD, 1.4 mm ID, 10-cm length, 0.1-mm pore diameter) attached to PVC hose were used to extract solution from soilless media at container capacity and analyzed for pH, EC, NO3-N and NH4-N. Media chemical properties were also analyzed by the Saturated Media Extract (SME) and Pour-Through (PT) methods. Extraction and analyses were conducted in peat: vermiculite (PV) and peat: perlite (PP) media irrigated for 1 week with Hoagland solution at 0.25, 0.5, 1, 2 and 4x. A 10-mL syringe was used as the vacuum source (48.1 ± 0.5 kPa) for the solution samplers (SS), yielding ≈2–5 mL of solution over a 3-min period. Simple correlation coefficients for EC, NO3-N and NH4-N between SS and SME and PT were high (>0.99). When measured by PT, these chemical properties were similar to SS (within 1% to 6%), whereas SME values were much lower than SS (12% to 15% and 35% to 38% in PV and PP media, respectively). Correlation coefficients for pH were lower than in other chemical properties, particularly in the PV medium. With an estimated life of ≈6 months in soil, SS are excellent monitoring tools for mineral nutrition research and horticultural crop production.