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Brian E. Jackson, Amy N. Wright, and Jeff L. Sibley

In the southeastern United States, inconsistent pine bark (PB) supplies and overabundance of cotton gin by-products warrant investigation about the feasibility of replacing PB with cotton gin compost (CGC) for container horticultural plant production. Most research on the use of composted organic substrates for horticultural plant production has focused on shoot growth responses, so there is a need to document the effect of these substrates on root growth. In 2004, `Blitz' tomato (Lycopersicon esculentum), `Hot Country' lantana (Lantana camara `Hot Country'), and weeping fig (Ficus benjamina) were placed in Horhizotrons to evaluate root growth in 100% PB and three PB:CGC substrates containing, by volume, 60:40 PB:CGC, 40:60 PB:CGC, and 0:100 PB:CGC. Horhizotrons were placed in a greenhouse, and root growth in all substrates was measured for each cultivar. Physical properties (total porosity, water holding capacity, air space, and bulk density) and chemical properties (electrical conductivity and pH) were determined for all substrates. Physical properties of 100% PB were within recommended guidelines and were either within or above recommended ranges for all PB:CGC substrate blends. Chemical properties of all substrates were within or above recommended guidelines. Root growth of all species in substrates containing CGC was similar to or more enhanced than root growth in 100% PB.

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Brian E. Jackson, Joe M. Kemble, Amy N. Wright, and Jeff L. Sibley

Tomatoes are the most abundantly produced greenhouse vegetable crop in the United States. The use of compost substrates has increased in recent years for the greenhouse production of many vegetables, bedding plants, and nursery crops. `Blitz' tomatoes were grown during the spring and fall growing seasons in 2004 in six substrate blends of pine bark (PB), a traditional production substrate in the Southeastern U.S., and cotton gin compost (CGC), an agricultural by-product, to assess the potential use of CGC as a viable replacement for PB for the production of greenhouse tomatoes. Treatments ranged from 100% PB to 100% CGC. During both growing seasons, plants grown in substrates containing CGC produced similar total, marketable, and cull yields compared to plants grown in 100% PB. Substrates containing 40% or more CGC had significantly higher EC levels both initially and throughout both growing seasons than did 20% CGC and 100% PB blends. Initial and final pH of all substrates was similar during both studies and remained within recommended ranges for greenhouse tomato production. Water-holding capacity increased as the percent CGC increased in each substrate blend, indicating the need for less irrigation volume for substrates containing CGC compared to the 100% PB control. Results indicate that CGC can be used as an amendment to or replacement for PB in greenhouse tomato production.

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Brian E. Jackson, Robert D. Wright, and Jake F. Browder

Many industrial and agricultural wastes have been evaluated for use as alternative container substrate components. Recently, a new material produced from ground pine logs (Pinus taeda L.) has been utilized as a substitute for peat moss and pine bark (PB). On 17 Aug. 2005, japanese holly (Ilex crenata `Compacta' Thunb.) plants were potted in milled PB (Pinus taeda L.) and debarked ground pine chips (PC). Pine chips were ground with a hammermill to pass through a 6.35-mm screen. Osmocote Plus 15–9–12 (15N–4P–10K) was incorporated in both PB and PC substrates at the rates of 3.5, 5.9, 8.3, and 10.6 kg·m-3. Plants were greenhouse grown until 22 Nov. 2005. Substrate solution nutrient content and pH were determined for all treatments in each substrate. Shoots were dried, weighted, and tissue analyzed for N, P, K, Ca, Mg, S, Fe, Cu, Mn, and Zn. Shoot weights were higher in plants grown in PB than PC at the 3.5 and 5.9 kg·m-3 fertilizer rates. At the 8.3 kg·m-3 rate, shoot dry weight was about the same for each substrate, but at the 10.6 kg·m-3 rate, growth was higher for plants grown in PC than in PB. Substrate EC increased with increasing fertilizer rates and with the exception of Cu, was higher in PB substrates at all fertilizer rates. Plant tissue levels generally increased as fertilizer rate increased in both substrates but were higher in plants grown in PB than PC with the exception of Cu. Therefore, higher rates of fertilizer are required to produce optimal plant growth in PC compared to PB.

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Amy N. Wright, Alex X. Niemiera, J. Roger Harris, and Robert D. Wright

The objective of this study was to determine the effects of lime and micronutrient amendments on growth of seedlings of nine container-grown landscape tree species in two pine bark substrates with different pHs. Acer palmatum Thunb. (Japanese maple), Acer saccharum Marsh. (sugar maple), Cercis canadensis L. (redbud), Cornus florida L. (flowering dogwood), Cornus kousa Hance. (kousa dogwood), Koelreuteria paniculata Laxm. (golden-rain tree), Magnolia ×soulangiana Soul.-Bod. `Lennei' (magnolia), Nyssa sylvatica Marsh. (blackgum), and Quercus palustris Müenchh. (pin oak) were grown from seed in two pine bark substrates with different pHs (pH 4.7 and 5.1) (Expt. 1). Preplant amendment treatments for each of two pine (Pinus taeda L.) bark sources were: with and without dolomitic limestone (3.6 kg·m–3) and with and without micronutrients (0.9 kg·m–3), and with and without micronutrients (0.9 kg·m–3), supplied as Micromax. Seedlings were harvested 12 and 19 weeks after seeds were planted, and shoot dry weight and tree height were determined. The same experiment was repeated using two of the nine species from Expt. 1 and pine bark substrates at pH 5.1 and 5.8 (Expt. 2). Seedling shoot dry weight and height were measured 11 weeks after planting. For both experiments, pine bark solutions were extracted using the pour-through method and analyzed for Ca, Mg, Fe, Mn, Cu, and Zn. Growth of all species in both experiments was greater in micronutrient-amended than in lime-amended bark. In general, adding micronutrients increased nutrient concentrations in the pine bark solution, while adding lime decreased them. Effect of bark type on growth in Expt. 1 was variable; however, in Expt. 2, growth was greater in the low pH bark than in the high pH bark. In general, nutrient concentrations in bark solutions were higher in low pH bark than in high pH bark for both experiments. Under the pH conditions of this experiment, micronutrient additions stimulated growth whereas a lime amendment did not.

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Helen H. Tyler and Stuart L. Warren

An experiment with a factorial treatment combination in a split plot design with five single plant replications was conducted to evaluate the effects of five rates of fertilizer addition and two irrigation volumes on plant growth in a composted turkey-litter-amended pine bark substrate. Main plots were daily applications of 600 or 900 ml/3.8-L container. Subplots were either 0, 1.0, 2.0, 3.0, or 4.0 g N additions (Osmocote High H 24N–1.7P–5.8K) per container topdressed on a substrate composed of pine bark amended with 8% (by volume) composted turkey litter. No additional amendments were made to the compost amended substrates. An additional “industry control” treatment consisted of an 8 pine bark: 1 sand (by volume) substrate amended with 3.0 kg/m3 dolomitic limestone and 0.9 kg/m3 Micromax and topdressed with 3.5 g N (Osmocote High N) per container. After 134 days, Cotoneaster dammeri `Skogholm' and Rudbeckia fulgida `Goldsturm' plants were harvested and shoot and root (cotoneaster only) dry weights were determined. Cotoneaster shoot and root dry weights and rudbeckia shoot dry weight increased linearly as N rate increased from 0 to 4.0 g N. Irrigation volume did not affect cotoneaster shoot or root dry weights. Rudbeckia shoot dry weight was 18% greater with 900 ml than with 600 ml of irrigation. Rudbeckia growth in compost amended substrate was greater than in the industry control when topdressed with ≥1.0 g N. Shoot growth of cotoneaster in the industry control substrate and compost amended substrate with ≥ 3.0 g N applied was similar.

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Carleton B Wood, Timothy J. Smalley, and Mark Rieger

Container-grown Viburnum plicatum var. tomentosum `Mariesii' were planted in tilled beds and tilled beds amended with aged pine bark. After transplanting, plants were fertilized at three different rates: no fertilizer, 18.4 g of N m-2, and 36.8 g of N m-2. A 31 day drought was begun 73 days after planting. Fertilization of tilled plots induced ammonium toxicity, which caused a linear reduction in leaf area, shoot dry weight, and root dry weight. Fertilization of amended plots had no effect on shoot growth but reduced mot growth by 54%; thus, amendments ameliorated ammonium toxicity. Between 10 and 28 days after beginning the drought, plants in unfertilized-amended plots maintained higher relative leaf water contents (RLWC) and relative leaf expansion rates (RLER) than plants in unfertilized-tilled plots. Amendment induced nitrogen deficiencies contributed to the increased drought tolerance of plants from unfertilized-amended plots. Since fertilized plants developed symptoms of ammonium toxicity, we were unable to determine if increasing fertility would counteract the drought tolerance conferred by pine bark soil amendments.

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Steven E. Newman and Jesse R. Quarrels

The objective of this study was to determine the influences of 8 commercial media, 4 peat-based and 4 pine bark-based, on the effects of uniconazole applied as a media drench to `Gutbier V-14 Glory' poinsettias. The peat-based media were Baccto Grower's Mix, Baccto High Porosity Professional, Baccto High Porosity Professional with Bacctite, and Baccto Rockwool Mix. The pine bark-based media were Metro 300, 360, 500, and 700. Uniconazole was applied to plants grown in each media at 5 rates (0, 2, 4, 6, and 8 mg · 15 cm por1).

Uniconazole effectively reduced plant height and width, bract dry weight, and bract number in all media. Plants grown in the Metro products, however, tended to be larger than those grown in the Baccto products. Bract size and number, plant weight, width and height were greatest in Metro 360. The rockwool mix produced the smallest plants. Plants grown in the peat-based media were more sensitive to uniconazole drenches. Plants grown in Metro 360 were the least sensitive to uniconazole drenches.

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James S. Owen Jr., Stuart L. Warren, Ted E. Bilderback, and Joseph P. Albano

The physical and chemical properties of pine bark yield low water and nutrient efficiency; consequently, an engineered substrate altering the substrate properties may allow greater water and nutrient retention. Past research has focused on controlling the quantity and rate of water and nutrient inputs. In this study, pine bark was amended at 8% (by volume) with a Georgiana palygorksite-bentonite blended industrial mineral aggregate with a particle size of 850 μm-4.75 mm or 300 μm-710 μm to improve water and nutrient efficiency. Each particle size was pretreated at temperatures of ≈140 °C (pasteurized) or ≈390 °C (calcined). The study was a 2 (particle size) × 2 (heat pretreatment) factorial in a randomized complete-block design with four replications. The control was a pine bark substrate amended with 11% sand (by volume). Containers (14 L) were topdressed with 17–5–12 controlled release fertilizer. A 0.2 leaching fraction was maintained by biweekly monitoring container influent from spray stakes and effluent volume measured daily. An aliquot of the daily collected effluent was analyzed for phosphorus (P). After 112 days, tops and roots were harvested, dried, and weighed for dry weight comparisons. Compared to pine bark amended with sand the 300 μm-710 μm particle size mineral decreased mean daily water application by ≈0.4 L/day per container. The calcined mineral reduced P leaching by ≈10 mg of P per container or 60% over the course of the study compared to pine bark: sand. Top and root dry weights were unaffected. These results suggest 300 μm–710 μm calcined mineral provided the most significant decreases in water use and P leaching while growing an equivalent plant.

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John D. Lea-Cox and I.E. Smith

Pine bark and peat-based substrates have been shown to have low-phosphorus (P) fixation capacity and high leach-potential, similar to that occurring in high-organic soils lacking in inorganic colloids. A long-term greenhouse experiment was conducted where three rootstock species of varying growth rate, Citrus jambhiri Lush.(RL), Citrus reshni Hort. ex Tan. (CM), and Poncirus trifoliata L. × Citrus sinensis L. (Osbeck) (CC), were grown in 3-L containers in composted pine bark, amended with three forms of P. Two slowly soluble forms (Calmafos and MagAmp) and soluble single superphosphate were incorporated at 0 (control), 200, 400, and 800 g P/m3, in a completely randomized block design (n = six plants). A split fertigation treatment of P at 50 mg·L–1 vs. No P was superimposed on the design (n = 3). Despite significant (P > 0.01) differences in P availability in the substrate after 380 days, particularly between liquid P (μ = 65 mg·L–1) vs. no liquid P (μ = 15 mg·L–1), differences in leaf analysis of seedlings after 235 days showed little significance (2.2 vs. 2.7 mg·g–1). To avoid excessive leaching of P from pine bark substrates, it therefore appears that slow-release forms of P are adequate to maintain relatively high growth rates of citrus stock without supplemental P fertigation.

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Jesse R Quarrels and Steven E. Newman

A study was conducted to determine the effects of pine bark grind size and pine bark levels on the activity of two growth regulators on poinsettia Two bark grinds (≤ 6 mm and >10 mm) were used with four media combinations within each grind: vermiculite:bark:peat moss at 2:0:3, 2:1:2, 2:2:1, and 2:3:0 (by volume). Two growth regulators, paclobutrazol and uniconazole, were applied at 0, 0.125, and 0.250 mg/15 cm container in 250 ml water. Two poinsettia cultivars, `Freedom' and `Gutbier V-14 Glory', were planted September 2, 1993, pinched September 16, and growth regulators applied September 30. There were five single plant replications for each treatment. Stem length and bract area were effected by bark grind, bark level, growth regulator, and growth regulator rate. Plants treated with uniconazole had the shortest stems and the least bract area. Plants grown in the smaller grind and at higher bark levels were less effected. Plants treated with paclobutrazol had longer stems than those treated with uniconazole.