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  • Author or Editor: Charles H. Gilliam x
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Over the past three decades, one issue that has received significant attention from the scientific community is climate change and the possible impacts on the global environment. Increased atmospheric carbon dioxide (CO2) concentration along with other trace gases [i.e., methane (CH4) and nitrous oxide (N2O)] are widely believed to be the driving factors behind global warming. Much of the work on reducing greenhouse gas emissions and carbon (C) sequestration has been conducted in row crop and forest systems; however, virtually no work has focused on contributions from sectors of the specialty crop industry such as ornamental horticulture. Ornamental horticulture is an industry that impacts rural, suburban, and urban landscapes. Although this industry may have some negative impacts on the global environment (e.g., CO2 and trace gas efflux), it also has potential to reduce greenhouse gas emissions and increase C sequestration. The work described here outlines the causes and environmental impacts of climate change, the role of agriculture in reducing emissions and sequestering C, and potential areas in ornamental horticulture container-grown plant production in which practices could be altered to increase C sequestration and mitigate greenhouse gas emissions.

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Residual chipping material, also called clean chip residual (CCR), has potential use as a growth substrate in the nursery and greenhouse horticultural industries. A survey was conducted in the southeastern United States among companies conducting harvesting operations on pine (Pinus sp.) plantations for the production of pulpwood in the forest industry. Fourteen operators in four states (Alabama, Mississippi, Georgia, Florida) were visited to evaluate the on-site status of residual material. Sample analysis of CCR revealed that it was composed of ≈37.7% wood (range, 14.2% to 50.5%), 36.6% bark (range, 16.1% to 68.5%), 8.8% needles (range, 0.1% to 19.2%), and 16.9% indistinguishable (fine) particles (range, 7.5% to 31%). pH ranged from 4.3 to 5.5 for all locations and electrical conductivity (EC) averaged 0.24 mmho/cm. Most nutrients were in acceptable ranges for plant growth with the exception of three sites above recommended levels for iron and four sites for manganese. Survey participants estimated that ≈27.5% of the harvest site biomass was composed of CCR. Some harvesters were able to sell CCR as fuelwood to pulp mills, while others did not recover the residual material and left it on the forest floor (44.3% total site biomass). Operations in this survey included typical pine plantation chipping and grinding operations (harvesters), woodyards (lumber, fuelwood, etc.), and operations processing mixed material (salvage from trees damaged in hurricanes or mixed tree species cleared from a site that was not under management as a plantation). Residual material varied depending on the plantation age, species composition, site quality, and natural actions such as fire. Average tree age was 11.5 years (range, 8 to 15 years), while average tree stand height was 37.0 ft (range, 25 to 50 ft) and average diameter at breast height (DBH) was 5.9 inches (range, 4 to 7 inches). Residual material on site was either sold immediately (28.6%), left on site for 1 to 3 months (28.6%), left on site for up to 2 years (7.1%), or not collected/sold (35.7%). Several loggers were interested in making CCR available to horticultural industries. Adequate resources are available to horticultural industries, rendering the use of CCR in ornamental plant production a viable option.

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Effects of combining labeled rates of halosulfuron (Sandea) and s-metolachlor (Dual Magnum) were evaluated as a preemergence (PRE) application in a randomized complete block designed experiment at the Wiregrass Experiment Station in southeastern Alabama. Treatments were assigned in a factorial arrangement of four levels of halosulfuron (0.0, 0.009, 0.018, and 0.036 lbs. a.i./acre) and six levels of s-metolachlor (0.0, 0.25, 0.50, 0.75, 1.0, and 1.25 lbs. a.i/acre). The purpose of the study was to ascertain possible synergistic effects from combining these two herbicides to control nutsedge at a possible lower cost. Two repetitions were completed in 2005 with data pooled in analysis. Results found no interaction between the halosulfuron and the s-metolachlor and therefore no synergistic affects. Analysis of the main effects revealed that the highest labeled rate of either herbicide gave the highest percent control relative to the nontreated control. Soil activity of halosulfuron in controlling nutsedge has been shown to be less effective than foliar applications. Our own LD90 greenhouse studies confirmed this to be true. We examined four application techniques of halosulfuron (POST both soil and foliar, POST foliar only, POST soil only, and PRE soil only) to determine the LD90. Results revealed that halosulfuron had the lowest LD90 from the treatments with a foliar application. However, some soil activity was observed. Results from field studies indicated that PRE applications of halosulfuron must be at the highest labeled rate to provide effective control. S-metolachlor was equal to halosulfuron on percent control and is lower in cost on a per acre basis.

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Twelve red maple selections in an existing field trial were evaluated for leaf chlorophyll content with a SPAD-502 chlorophyll meter, total foliar N concentration with a LECO CHN analyzer, and total foliar chlorophyll content (CHL) by N,N-dimethylformamide extraction. Selections included Acer rubrum L. `Autumn Flame', `Fairview Flame', `Franksred' (Red Sunset™), `Karpick', `Northwood', `October Glory', `Redskin', `Schlesingeri', and `Tilford', and A. ×freemanii E. Murray `AutumnBlaze' (`Jeffersred'), `Morgan' (`Indian Summer'), and `Scarsen' (Scarlet Sentinel™). `Franksred' and `Northwood' had the highest monthly SPAD-502 values in 1993 and 1994. Lowest SPAD-502 values were on `Redskin' and `Autumn Blaze' each year. Foliar N concentration ranged from 2.62% for `Autumn Flame' to 2.01% for Redskin. CHL levels on a fresh-weight basis ranged from 5.38 mg·g–1 for `Fairview Flame' to 3.94 mg·g–1 for `October Glory'. SPAD-502 and extractable CHL values were correlated (r = 0.45; P ≤ 0.001); however, the correlation (r = 0.15; P ≤ 0.38) between SPAD-502 values and total foliar N concentration was nonsignificant.

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Regalia®, a commercial extract of giant knotweed [Fallopia sachalinensis F. Schmidt (synonyms: Reynoutria sachalinensis (F. Schmidt) Nakai, Polygonum sachalinense F. Schmidt, Tiniaria sachalinesis (F. Schmidt) Janch.)], was evaluated for its potential to enhance drought tolerance of container-grown impatiens (Impatiens walleriana Hook. f. ‘Super Elfin XP White’). In two separate experiments, Regalia® was foliar-applied once a week for 4 weeks at four different rates (0, 5, 10, or 15 mL·L−1). In Expt. 1, Regalia® was applied to impatiens grown under three target substrate volumetric water contents (TVWCs): 85%, 55%, or 25%. In Expt. 2, Regalia® was applied to impatiens watered with 1, 3, or 6 days between waterings (DBW). In Expt. 1, root dry weight (RDW) of impatiens receiving applications of Regalia® at the 0.5× rate was greater compared with the 0.0× rate across all TVWCs. Additionally, soluble protein content was greater after Regalia® application at the 0.5×, 1.0×, or 1.5× rates compared with the 0.0× rate for plants grown at 55% TVWC. In Expt. 2, leaf greenness (SPAD) and leaf net photosynthetic rate (Pn) were greater with Regalia® applied at the 0.5× and 1.0× rates compared with the 0.0× rate, respectively. Soluble protein content was greater in impatiens treated with Regalia® at the 1.5× rate and 1 DBW and the 0.5× rate with 3 DBW compared with the 0.0× rate with 1 or 3 DBW. However, there was no indication that impatiens grown under different moisture levels had increased drought tolerance after application of Regalia®.

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Adsorption, mobility, and filtration ability of organic media toward metolachlor were evaluated in a series of laboratory experiments. Experimental variables included media type, metolachlor concentration, and equilibration time. Adsorption isotherms were determined by applying the log form of the Freundlich equation. Mobility was evaluated using glass columns filled with media, which were then surface spiked with metolachlor and then leached daily for 10 consecutive days. Peat, pine bark, combinations of these two media and a mixture of pine bark and sand adsorbed >90% of the 14C metolachlor. Freundlich sorption coefficients were 10.9, 18.2, 13.4, 14.2, and 11.0 for pine bark, peat, 5 pine bark: 1 peat, 3 pine bark: 1 peat, and 5 pine bark: 1 sand, respectively. In a timed exposure experiment using bark, minimum metolachlor adsorption (57%) was at 90 seconds and maximum adsorption (82%) required at least 1440 minutes. In column leaching studies, data for all media indicate that metolachlor is relatively immobile through these substrates. An initial pulse of metolachlor (<1.0 μg·liter-1) was detected with each medium up to the third wetting event with a subsequent decline (>0.5 μg·liter-1 for each medium) in the metolachlor recovered. Filtration efficiency of commercially formulated metolachlor from water passed through different lengths of pine bark filled filters was 0%, 17%, 20%, 22%, 23%, and 29% for filters 4, 20, 12, 8, 16, and 24 cm in length, respectively. These results support the contention that such filtration would be effective provided the residence time of water within the filter was sufficient for adsorption of the contaminant by the media to occur.

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Two commonly used management practices for weed control in container plant production are hand pulling and herbicide applications. There are problems associated with these methods including crop phytotoxicity and environmental concerns associated with off-target movement of herbicides. Other nonchemical weed control methods could reduce herbicide-based environmental concerns, mitigate herbicide-resistance development, and improve the overall level of weed control in container nursery production. Readily available tree-mulch species, eastern red cedar (Juniperus virginiana), ground whole loblolly pine (Pinus taeda), chinese privet (Ligustrum sinense), and sweetgum (Liquidambar styraciflua) were harvested, chipped, and evaluated at multiple depths with and without the herbicide dimethenamid-p. Pine bark mini-nuggets were also evaluated. Mulches were applied at depths of 1, 2, and 4 inches and evaluated over three 30-day periods for their effectiveness in suppressing spotted spurge (Chamaesyce maculata), long-stalked phyllanthus (Phyllanthus tenellus), and eclipta (Eclipta prostrata). After 30 days, herbicide/mulch combinations, as well as mulch treatments alone, had reduced weed fresh weight 82% to 100% with 1 inch of mulch. By 168 days after treatment, dimethenamid-p had lost all efficacy, and mulch depth was the only factor that still had significant effects, reducing spotted spurge fresh weight by 90%, 99.5%, and 100% with depths of 1, 2, and 4 inches, respectively. The economics of mulch weed control will depend on variables such as available time, nursery layout, location, and availability of resources, equipment, among others. Regardless of variable economic parameters, data from this study reveals that any of these potential mulch species applied at a depth of at least 2 inches will provide long-term weed control in nursery container production.

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