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  • Author or Editor: Nina Bassuk x
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In the development of a street tree planting medium for use as a sidewalk base, we have been testing a series of limestone gravel and soil media with varied amounts of clay loam suspended within the matrix voids. Tilia cordata and Quercus alba seedling roots quickly penetrated and grew in these systems when compacted to densities in excess of 2000 kg·m–3, while they were severely impeded in clay loam soil compacted to 1300 kg·m–3. Limestone mixes of the same design had variable, but consistently acceptable, California Bearing Ratios (>40) when compacted to similar densities; demonstrating their strength as a pavement base. Tilia root growth, based on the volume collected from total root excavations after two growing seasons, increased a minimum of 300% in the limestone mixes over the compacted clay loam control when the treatments were compacted to ≈80% Standard Proctor Optimum Density. Root penetration of Quercus increased >400% in the limestone mixes over compacted loam in a 6-month trial compacted to 95% Standard Proctor Optimum Density.

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CU soil is a material primarily composed of clay loam soil and crushed stone designed for use under pavement to promote street tree root growth in a durable pavement section, such as sidewalks or parking lots. One concern is the low total soil fraction from which tree roots can meet nutritive demands. At issue is the long-term nutrient management of street trees once the root zone has been rendered inaccessible due to the pavement wearing surface, although in 3-year field tests, there were no differences found between a CU soil material and an agricultural field control. CU soil treatments were produced in a factorial design with a patent applied for processed humate additive, and a nursery production fertilization treatment. Bare-root seedlings of Salix nigra Marsh, Platanus × acerifolia Willd., Ginkgo biloba L., and cell plugs of Ficus benjamina L. were grown in treatment containers for 5 months. A Minolta SPAD-502 was used to evaluate relative chlorophyll content as an indication of leaf tissue nutrient levels. Plant growth as a function of new growth dry weight was calculated. Soil samples were collected at the end of the study and were analyzed to evaluate the impact of humate admixes in nutrient availability. The fertilization treatments positively influenced leaf color and growth for all species. The CU soil control plants displayed significantly lower chlorophyll levels, but overall growth differences were less dramatic—insignificant in some cases. The humate additive did not consistently affect leaf color. The humate additive alone did not affect plant growth, but a significant positive interaction with the fertilizer treatment was evident for Platanus and Ficus. The positive interaction was insignificant in Salix and non-existent in Ginkgo.

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CU soil is a material primarily composed of clay loam soil and crushed stone designed for use under pavement to promote street tree root growth in a durable pavement section, such as sidewalks or parking lots. One concern is the low total soil fraction from which tree roots can meet nutritive demands. At issue is the long-term nutrient management of street trees once the root zone has been rendered inaccessible due to the pavement wearing surface, although in 3-year field tests, there were no differences found between a CU soil material and an agricultural field control. CU soil treatments were produced in a fractional factorial design with a patent applied for, processed humate additive, a nursery production fertilization treatment, and a mycorrhizae inoculation package of Pt and various VAM species. The mycorrhizae/fertilizer treatment was eliminated for plant availability restrictions. Bare-root seedlings of Salix nigra Marsh. were grown in treatment containers for 5 months. A Minolta SPAD-502 was used to evaluate relative chlorophyll content as an indication of leaf tissue nutrient levels. Plant growth as a function of root dry weight, shoot dry weight, and shoot: root ratio was analyzed. Soil analyses were conducted on media samples collected at the end of the study to evaluate the impact of humate admixes in nutrient availability. The fertilization treatments positively influenced leaf color, shoot weight, root weight, and shoot: root ratio. There was no impact from the mycorrhizae inoculation on leaf color or growth. There was no impact from the humate additive on leaf color or growth. There were no additive effects found in the treatment levels.

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Two experiments were conducted to determine the effect of severe stock plant cutback on rooting in two oak species Quercus bicolor and Quercus macrocarpa using two propagation systems, layering and cuttings. In experiment 1, field grown plants were either cutback leaving a 0.04 m (1.6 in.) stump above soil level or left intact (not cutback) ≈1.7 m (66.9 inches) tall. Shoots arising from cutback treatments and intact plants were layered using a field layering technique and air layering respectively. Results showed significantly higher (p < 0.01) rooting percentages in layered propagules arising from severely cutback plants in both species [≈77% in Quercus bicolor and ≈70% inQuercus macrocarpa] compared with air layered shoots arising from intact plants [1% in Quercus bicolor and 0% in Quercus macrocarpa]. In experiment 2, shoots arising from three stock plant heights (severely cutback 0.04 m, cutback 1 m and intact ≈1.7 m plants) were either etiolated or grown in full light and cuttings rooted in a perlite medium under mist. Of the two species studied, propagule position was found to have no significant effect on rooting in Quercus macrocarpa cuttings, but significantly (p < 0.0001) influenced rooting in Quercus bicolor. Rooting was highest 59.3% in cuttings taken from cutback-etiolated stock plants. Comparing just the three cutback levels, rooting was highest (45.2%) in cuttings arising from 0.04 m stumps followed by those from 1 m stumps 7.5% and lastly intact plants 3.8%. The best rooting results were observed in shoots arising from severely cutback stock plants (0.04 m) using the field layering technique.

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Abstract

The discovery and use of auxins in rooting and the development of mist propagation are unequivocal milestones in the history of propagation due to their broad applicability and effectiveness. Stock plant etiolation may prove to be in a similar class with these techniques. The practical use of stock plant etiolation to improve rooting in cuttings has largely been spurred on in the past 10 years by the successes achieved by Howard and others at the East Mailing Research Station, United Kingdom (9). For all the renewed interest, however, the practice of withholding light to improve propagation is probably an ancient one, having been employed every time a stool bed or layer was made or even a cutting inserted into opaque media.

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Impressive ornamental features including exfoliating bark and golden fall color are among the reasons why hickories [Carya (Nutt.)] are sought after by horticulturists. Their potential for application in the green industry continues to grow as producers and consumers in the United States become more interested in adopting native plants; however, an absence of knowledge that defines which species are tolerant of abiotic stresses in the landscape limits their use. If production of stress-tolerant hickories increases, they could be used to diversify urban forests and may bolster the resiliency of managed landscapes. We examined the predicted leaf water potential at the turgor loss point to estimate drought tolerance among several species of hickories and pecans adapted to growing in northern climates in the United States. Our hypotheses were that because some bottomland habitats experience seasonal drought in addition to flooding, taxa adapted to these sites may be more drought tolerant than previously assumed, and that the degree of drought tolerance would be variable within species and populations. Predicted mean leaf turgor loss measured in summer across species was −3.38 MPa. Kingnut hickory [Carya laciniosa (F. Michx.) Loud.] exhibited the lowest mean summer leaf turgor loss point −3.64 MPa), whereas pignut hickory [Carya glabra (Mill.) Sweet.] exhibited the highest (−3.20 MPa). Provenance of trees studied influenced estimated drought tolerance of C. laciniosa. Variability between individual trees within each species was observed, suggesting clonal selections of each taxon can be made for drought-prone landscapes. The results of this work imply that all the species studied are at least moderately drought tolerant and should be considered for planting in managed landscapes. Further, species often associated with riparian habitats may exhibit substantial tolerance to drought and should not be excluded from use on drought-prone sites.

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Effects of stockplant etiolation, stem banding, exogenous auxin, and catechol on the rooting response of softwood cuttings of paperbark maple (Acer griseum Pax.) were studied. Etiolated cuttings rooted better than light-grown cuttings, while stem banding did not affect rooting percentage (light-grown, 10%; light-grown + banding, 18%; etiolated, 41%; etiolated + banding, 37%). IBA did not promote, but catechol inhibited rooting (control, 31%; IBA, 37%; catechol, 17%; IBA + catechol, 21%). Root number was increased by IBA and unaffected by catechol. The distance from the cutting base to the first emerged root was measured as an indication of auxin toxicity. IBA interacted with etiolation and stem banding to increase this distance, which was greater in catechol-treated cuttings. Chemical names used: 1,2-benzenedio1 (catechol); 1H-indole-3-butanoic acid (IBA).

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The effects of silver thiosulfate (STS) on stored and freshly made cuttings of `Royalty' rose (Rosa hybrids) were examined in relation to rooting and subsequent budbreak. STS pretreatment at 0.5 mm during storage stimulated budbreak but decreased the percentage of cuttings that rooted and the number of roots. IBA at 4.9 to 9.8 mm inhibited budbreak but this effect was partially reversed by STS. Spraying the cuttings with 1.0 mm STS once daily during the first 5 days of the rooting period also reduced rooting but prevented IBA-induced leaf senescence. Ethephon and spermine, each applied at 0.5 mm before rooting, had no effect on rooting or budbreak. Chemical names used: (2-chloroethyl)-phosphonic acid (ethephon); indole butyric acid (IBA); N,N'-bis(3-aminopropyl) -l,4-buanediamine (spermine).

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Softwood shoots of apple (Malus domestica Borkh.) rootstocks M.9 and MM.106 were banded with Velcro for up to 20 days before cuttings were propagated. Percent rooting and the number of roots per cutting were significantly improved by banding for 10 to 20 days, with and without IBA application. As the duration of stem banding increased from 0 to 20 days, percent rooting and the number of roots of both M.9 and MM.106 cuttings increased linearly or curvilinearly. Stem banding also stimulated budbreak of cuttings. In M.9, banding resulted in a higher survival rate and increased new shoot growth of transplanted cuttings after 4 months. Percent budbreak and new shoot growth were highly correlated with the number of roots per cutting in both cultivars. The effects of stem banding on budbreak and subsequent growth of the cuttings were largely due to the enhanced rooting of cuttings. Chemical names used: 1H-indole3-butyric acid (IBA).

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The Minolta SPAD meter has been used to evaluate chlorophyll concentration in plant material to provide an inexpensive method to collect rapid, nondestructive data. Correlations of SPAD data and chlorophyll concentrations in corn have been very accurate r 2 = 0.95), and can be used to monitor plant nutrient status as a function of chlorophyll concentration. There has been evidence that the calibrated accuracy of the SPAD meter is diminished at low and high concentrations of chlorophyll. Our study attempted to build the same type of background information for two tree species for use in evaluating plant response in experimental media experiments. Ficus benjamina L. and Populus deltoides Marsh were grown in containers of varied media. Leaf tissue was measured with a Minolta SPAD-502, and the tissue was then removed and processed with N,N-dimenthylformamide for analysis in a spectrophotometer. The remainder of the leaf sample was analyzed in an ICAP for tissue nutrient levels. Data were analyzed to evaluate the usefulness of the SPAD meter for woody plant leaf tissue evaluation and to develop calibration curves for use in future studies. There was a positive correlation (r 2 = 0.943 in Ficus) between SPAD data and combined concentrations of chlorophyll a and b. Accuracy of the SPAD data was diminished when chlorophyll concentrations were low (SPAD <20, chorophyll <450 μg·mL-1) and high (SPAD >45, chorophyll >1350 μg·mL-1)..

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