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  • Author or Editor: William R. Graves x
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Carolina buckthorn [Rhamnus caroliniana Walt. or Frangula caroliniana (Walt.) Gray] is an attractive and water-stress-resistant shrub or small tree distributed extensively in the southeastern United States that merits use in managed landscapes. Due to substantial climatic differences within its distribution (30-year normal midwinter minima range from 13 to -8 °C), selection among provenances based on differences in cold hardiness is warranted. Before selections are marketed, the potential of carolina buckthorn to be invasive also merits investigation. Ecological problems resulting from the introduction of Rhamnus L. species in the United States, most notably the dominance of R. cathartica L. (common buckthorn) over neighboring taxa, are due in part to early budbreak. Consequently, we investigated depth of cold hardiness and vernal budbreak of carolina buckthorn and common buckthorn. Stem samples of carolina buckthorn and common buckthorn collected in midwinter survived temperatures as low as -21 and -24 °C, respectively. Although the cold hardiness of carolina buckthorns from Missouri was greater than that of carolina buckthorns from Ohio and Texas on 2 Apr. 2003, there were no differences in cold hardiness of stems from Missouri and Texas on all three assessment dates in the second experiment. All plants survived at both field locations except for the carolina buckthorns from southern Texas planted in Iowa, which showed 0% and 17% survival in 2003 and 2004, respectively. Budbreak of both species with and without mulch in Ames, Iowa, was recorded from 9 Apr. to 10 May 2002. Mean budbreak of common buckthorn was 5.7 days earlier than budbreak of carolina buckthorn, and buds of mulched carolina buckthorns broke 4.2 days earlier than did buds of unmulched carolina buckthorns. We conclude that the cold hardiness of carolina buckthorn is sufficient to permit the species to be planted outside of its natural distribution. Populations of carolina buckthorn in Ohio and Missouri should be the focus of efforts to select genotypes for use in regions with harsh winters. Phenology of its budbreak suggests carolina buckthorn will not be as invasive as common buckthorn, but evaluation of additional determinants of invasiveness is warranted.

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High temperatures are reported to promote day-neutral strawberry (Fragaria ×ananassa) vegetative growth and development and inhibit floral and fruit development, thereby imposing geographic and temporal limitations on fruit production. Day-neutral strawberry response to air temperature has been researched, but specific responses to temperature in the root zone have not. In a 1998 greenhouse experiment, 60 `Tristar' plants were grown hydroponically in a system of individual, temperature-controlled pots. A randomized complete-block design with constant root-zone treatments of 11, 17, 23, 29, and 35 °C and 12 replications were used. Stomatal conductance and transpiration rate were significantly lower for plants at 35 °C, compared with plants at all other temperatures. Leaf area and leaf dry mass of plants at 35 °C were five and four times smaller, respectively, than the combined mean for plants in all other treatments. Leaf area of runner tips was 450 and 44.5 cm2 at 11 and 35 °C, respectively, compared with that of plants at all other temperatures, 1552.1 cm2. Fruit dry mass was 14.5, 21.6, 25.5, 29.0, and 3.96 g per plant at 11, 17, 23, 29, and 35 °C, respectively. Root dry mass was highest at 11 and 17 °C and lowest for plants at 35 °C. The number of flowers, fruit, and inflorescences per plant was reduced at 35 °C, as were individual berry fresh mass and diameter. Overall, `Tristar' growth and development were near optimal at 17, 23, and 29 °C.

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Temperature, as a potential environmental stressor, interacts with photoperiod in floral initiation of June-bearing strawberries (Fragaria ×ananassa), such that high-temperature exposure can result in poor floral initiation. Our objectives were to examine the effects of various durations of high root-zone temperature on floral initiation and development and on vegetative growth and development. In a 1998 greenhouse experiment, hydroponically grown `Allstar' June-bearing strawberry plants were subjected day/night temperatures of 31/21 °C in the root zone for one, two, or three continuous periods (of ≈7 days), followed by exposure to 17 °C for the duration of the experiment. Control plants were raised at 17 °C in the root zone throughout the experiment. An additional temperature treatment was exposure to 31/21 °C in the root zone for two periods, each followed by a period at 17 °C. Plants were arranged in a randomized complete-block design with factorial treatments of duration of high root-zone temperature and harvest time. At the end of each period, plants were harvested and the apical meristems dissected for microscopic evaluation of vegetative and floral meristems and the stage of development of the primary flower. We observed floral initiation in all treatments after photoperiodic induction. However, exposure to 31/21 °C in the root zone during key periods of floral initiation in June-bearing strawberry may alter floral development.

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Freeman maples (Acer ×freemanii E. Murray) are suspected to be more resistant to environmental stress than red maples (A. rubrum L.) because the lineage of Freeman maple includes silver maple (A. saccharinum L.). Little is known, however, about stress resistance of silver maple, and few data from direct comparisons of red and Freeman maples are available. Our objectives were to determine effects of root-zone heat on silver maples from northern and southern provenances, and to compare red and Freeman maple cultivars for resistance to rootzone heat stress and drought. There were no provenance-by-temperature interactions when silver maples from 33.3°N (Mississippi) and 44.4°N (Minnesota) latitude were grown with root zones at 29 and 35°C. Plants from 44.4°N latitude had 36% higher fresh mass, 43% more leaf surface area, and 35% and 59% higher, respectively, root and shoot dry masses than plants from 33.3°N latitude. Midday xylem water potential was 68% more negative for plants at 35°C than for plants at 29°C, and transpiration rate was 129% less for plants with root zones at 35°C than for those with root zones at 29°C. During preliminary work with Autumn Flame and Franksred red maple and Indian Summer and Jeffersred Freeman maples, rooted cuttings were grown in 25 and 37°C root zones under both drought and nondrought conditions. Reductions in growth at 37°C were similar for all cultivars. Results of this work could influence development, marketing, and use of Freeman maples.

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As part of a project to develop and assess bio-based, biodegradable plastics for their potential to replace petroleum-based plastics in specialty-crop containers, we evaluated prototype containers made of protein-based polymers from soybean [Glycine max (L.) Merr.] for their effectiveness during production of plants in greenhouses and subsequent establishment of those plants outdoors. Our objective was to assess the function and biodegradation of soy-based plastic containers with special attention to whether a fertilizer effect results from degrading containers before and after plants are moved outdoors. In our first experiment, plants of tomato (Solanum lycopersicum L.) and pepper (Capsicum annuum L.) were grown in soy-plastic containers and control containers of petroleum-based (polypropylene) plastic under greenhouse conditions for 4 weeks. Each plant then was transplanted and grown in an outdoor garden plot for 5 weeks with the container removed, broken into pieces less than 4 cm in diameter, and installed beneath the roots of the transplant. Three additional experiments were performed: a greenhouse trial to quantify the relative concentration and form of plant-available nitrogen (N) released from soy-plastic containers of three types [soy plastic, soy plastic coated with polylactic acid (PLA), and soy–PLA polymer blended 50:50 by weight] during production; a greenhouse trial to evaluate the same three container types under production conditions with five container-crop species; and a field trial to assess the effects of the 50:50 soy–PLA container on transplant establishment. Plant-available N was released from soy-based plastic containers during greenhouse production, and transplant establishment was enhanced when the soy-based container was removed, crushed, and installed in the soil near plant roots. During greenhouse production, containers of high-percentage soy plastic released N at an excessive rate (623 mg·L−1 in leachate) and predominantly in the form of NH4 + (99.4% at 3 weeks of culture). Containers made by blending soy plastic with PLA released N at a favorable rate during production. In both field trials, growth and health of plants cultured in soy containers were better than those of controls. Although the design and material formulation of soy-plastic containers need to be improved to optimize container integrity and plant health during production, our results illustrate the potential to use soy-based plastics in biodegradable containers that release N at rates that promote growth and health of plants during greenhouse production and establishment of transplants outdoors.

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Drawbacks of traditional synthetic fertilizer led us to explore a biologically based (bio-based) alternative. Our objective was to quantify the efficacy of wastewater-grown algae pellets and pastes harvested from rotating algal biofilm systems as fertilizers for three crops, ‘Honeycomb’ marigold (Tagetes patula L.), ‘Beefsteak’ tomato (Solanum lycopersicum L.), and ‘Ambrosia’ sweet corn (Zea mays L.). Factorial experiments were designed for each crop with fertilizer type (algae pellets, algae paste, a synthetic controlled-release fertilizer, or a commercially available bio-based fertilizer from wastewater treatment) and substrate (commercial or custom-made) as factors. Shoot growth, shoot nutrient concentration, and substrate pH and electrical conductivity (EC) were affected by fertilizer, substrate, or their interaction. Algae pellets and paste supplied nutrients to all three species effectively, increasing shoot size, dry weight, perceived health, and nutrient concentrations compared with unfertilized controls. Notwithstanding some variability among crops, performance of algal materials was similar to that of the synthetic fertilizer and better than that of the commercial bio-based fertilizer. As a bio-based fertilizer that supplies plants with recycled nutrients sequestered from wastewater, wastewater-grown algae can reduce the impacts of mineral nutrition management in container-crop production by partially supplanting synthetic fertilizer use.

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Biocontainers made of coconut coir, paper, peat, wood, or other natural fibers are considered sustainable alternatives to containers made of petroleum-based plastics, but growers’ acceptance and use of fiber containers have been limited by their comparatively high cost, low strength and durability, and poor water-use efficiency (WUE). We hypothesized that coating fiber containers with biopolymers would improve their strength, durability, and WUE during plant production. We compared the effectiveness of fiber containers of coir, paper, and wood that were either uncoated or coated with one of four biopolymers [polyamide (PA), polylactic acid (PLA), polyurethane (PU), or tung oil (TO)], peat-fiber containers that were uncoated, and injection-molded containers made of petroleum-based plastic. Ease of coating was assessed, along with the cost and strength of containers, their effectiveness during greenhouse production of ‘Honeycomb’ marigold (Tagetes patula), ‘Autumn Bell’ pepper (Capisicum annuum), ‘Madness Red’ petunia (Petunia ×hybrida), ‘St. John’s Fire’ salvia (Salvia splendens), and ‘Rutgers’ tomato (Solanum lycopersicum), and their WUE during production of salvia and tomato. Castor oil-based PU was the least expensive biopolymer coating and was easy to apply as a water-based dispersion. The other biopolymers required a hazardous and costly organic solvent (e.g., chloroform). Coatings of PA, PLA, and PU increased container strength and durability, and improved WUE during plant production. Coated paper-fiber containers resisted horizontal compression better than petroleum-plastic containers. Greenhouse-grown plants in containers coated with PA, PLA, or PU were larger and rated healthier and of better quality than plants grown in uncoated or TO-coated fiber containers. Plants grown in paper- and coir-fiber containers coated with PA, PLA, or PU were similar in health and size to plants grown in petroleum-plastic containers. Two coatings of PU on paper-fiber containers resulted in WUE similar to that of petroleum-plastic containers for both 4- to 5-inch and gallon sizes. Coating fiber containers with biopolymers slowed, but did not halt, their degradation in soil, indicating that decomposition in soil may be a suitable end-of-life option for biopolymer-coated fiber containers. Our results support the hypothesis that coating fiber containers with biopolymers can improve their effectiveness for crop production, while maintaining an improvement in sustainability over petroleum plastic. Paper-fiber containers coated with PU showed particular promise and were similar in material cost and performance to containers made of petroleum-based plastic.

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Bioplastics and bioplastic composites are a group of emerging sustainable materials that exhibit favorable characteristics for use in horticulture-production containers. Biocontainers made from composite materials of soy [Glycine max (L.) Merr.] bioplastic and poly(lactic) acid (PLA) have been shown to release nitrogen (N) at a rate suitable for supporting plant growth. We hypothesized that fertilizer applications can be reduced while maintaining adequate nutrition levels for plant production when using soy-based containers. To test this hypothesis and quantify potential reduction of fertilizer, we grew marigold ‘Honeycomb’ (Tagetes patula L.) in five prototypes of soy-composite biocontainers [soy bioplastic compounded with PLA or polyhydroxyalkanoates (PHA)] and a petroleum-plastic (polypropylene) control container with five fertilizer treatments supplying 1) 60N‒4P‒49K; 2) 75N‒5P‒61K; 3) 105N‒7P‒85K; 4) 150N‒10P‒122K; or 5) 300N‒20P‒244K mg. At harvest, plants grown in all soy‒PLA composite biocontainers and protein + PLA biocontainers had higher concentrations and contents of N and P compared with plants grown in petroleum-plastic containers across all fertilizer treatments. Shoot K concentrations were highest for plants grown in all soy‒PLA and soy‒PHA biocontainers compared with plants grown in petroleum-plastic containers across all fertilizer treatments, whereas shoot K concentrations in plants grown in protein + PLA biocontainers were equal to or lower than plants in petroleum-plastic containers. Total plant dry weight was greater for plants grown in biocontainers made of 50% soy‒50% PLA and protein + PLA than for plants grown in control containers across all fertilizer treatments except at the highest rate of fertilizer in which plants received 300N‒20P‒244K mg. Our results support the hypothesis that fertilizer inputs can be reduced when using soy-composite biocontainers. Biocontainers made with equal parts soy bioplastic and PLA showed strong potential for achieving adequate plant growth with reduced fertilizer input. Our results demonstrate that fertilizer can be reduced by as much as 80% when growing marigold in containers made of 50% soy‒50% PLA for 6 weeks.

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We evaluated emerging biopolymer horticultural products that provide fertilizer nutrients to plants (fertilizing biocontainers, pelletized biopolymer fertilizer, and biopolymer fertilizer spikes) for their effectiveness during greenhouse production and garden growth of floriculture crops, and during postproduction culture of container ornamentals. Greenhouse experiments (in 4.5-inch containers) and garden trials were performed with tomato (Solanum lycopersicum), pepper (Capsicum annuum), petunia (Petunia ×hybrida), and marigold (Tagetes patula). Postproduction experiments were performed with 12-inch hanging baskets containing lobelia (Lobelia erinus), trailing petunia (Calibrachoa ×hybrida), and petunia, and with 13-inch patio planters containing zonal geranium (Pelargonium ×hortorum), spikes (Cordyline indivisa), bidens (Bidens ferulifolia), and trailing petunia. Although slightly less effective than synthetic controlled-release fertilizer (CRF), all three nutrient-containing biopolymer horticultural products were sufficient and suitable for providing fertilizer nutrients to plants grown in containers and in garden soil. Results of the postproduction experiment provided proof-of-concept for the effectiveness and potential of biopolymer fertilizer spikes as a sustainable method for providing fertilizer nutrients to containerized plants. The current formulation of pelletized biopolymer fertilizer was somewhat more effective for vegetable crops (pepper and tomato) than for floriculture crops (marigold and petunia). For plants produced in 4.5-inch containers, the combination of the fertilizing biocontainer with no additional fertilizer in the greenhouse, then burying the fertilizing container beneath the plant to degrade and provide nutrients in the garden was very effective. Biopolymer horticultural products represent a promising alternative to petroleum-based plastic containers and synthetic fertilizers. Adoption of some or all of these technologies could improve the environmental sustainability of the horticulture industry without reducing productivity or efficiency, and without increasing labor intensity.

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We evaluated the effects of seven types of 4.5-inch top-diameter biocontainers and five rates of paclobutrazol drench on the growth and development of angelonia (Angelonia angustifolia ‘Serena White’) and petunia (Petunia ×hybrida ‘Wave® Purple Improved Prostrate’) during greenhouse production. The container types included were biopolyurethane-coated paper fiber; uncoated paper fiber; rice hull; coconut coir; peat; two types of bioplastic container, one made from 90% polylactic acid (PLA) and 10% lignin [PLA-lignin (90/10 by weight)] and another made from 60% PLA and 40% soy polymer with adipic anhydride {SP.A [PLA-SP.A]; (60/40 by weight)}; and a petroleum-based plastic control. All containers were filled with 590 mL of substrate composed of (by vol) 75% canadian sphagnum moss and 25% perlite. Ten days after transplanting seedlings, 2-fl oz aliquots of deionized water containing 0, 1, 2.5, 5, 10, or 20 mg·L−1 paclobutrazol were applied to the substrate surface as drenches. The date of anthesis was recorded for each plant, and growth data were collected 6 weeks after transplant. Shoots were harvested and dried and shoot dry weight (SDW) was recorded. Height (angelonia only) and diameter of angelonia and petunia and time to flower were calculated. Container type and paclobutrazol concentration interacted to affect size and SDW of angelonia and petunia. Growth index of angelonia treated with 0 mg·L−1 paclobutrazol and grown in coir and peat containers was 19% to 29% and 29% to 38% smaller than that of plants in other container types, respectively. Diameter of untreated petunia grown in peat containers was similar to that of those grown in coir and uncoated paper fiber containers, but was smaller (10.9 to 13.5 cm) than that of plants grown in other container types. As paclobutrazol concentrations increased from 0 to 20 mg·L−1 treatments, SDWs of petunia grown in coir containers were suppressed by 23%, whereas plants grown in rice hull containers were up to 45% less. Our results indicate that growth suppression of angelonia and petunia grown in biocontainers using paclobutrazol drenches varies by the type of biocontainer. Producers should reduce paclobutrazol drench concentrations to produce plants of appropriate size if substituting coir or peat biocontainers for traditional petroleum plastics, whereas no adjustment in plant growth retardant (PGR) drench concentrations is required for plants produced in the other biocontainer types we evaluated.

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