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  • Author or Editor: Donald A. Horneck x
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An experiment was conducted to determine how pH and nutrient availability in douglas fir bark (DFB) substrates respond to lime and sulfur (S) rates. The treatment design was a two-by-nine factorial arrangement with two substrate types and nine pH-altering amendments. The two substrates were 100% DFB or 75 DFB:15 sphagnum peatmoss:10 pumice (by volume). Substrate pH-altering amendments included elemental S amended at either 0.6 or 2.4 kg·m−3; calcium carbonate amended at 0.6, 1.5, and 5.9 kg·m−3; calcium hydroxide amended at 4.4, 8.9, or 23.7 kg·m−3; and a nonamended control. All substrates were amended by incorporating 0.9 kg·m−3 Micromax micronutrients before potting and topdressing 8 g/pot of 14N–4.2P–11.6K Osmocote controlled-release fertilizer after potting. A group of controls was also maintained for each substrate that received no fertilizer amendment (no S, lime, Micromax, or Osmocote). Four containers of each treatment were randomly selected and harvested 4 and 8 weeks after potting. Amendment with S decreased pH with increasing rate, whereas both lime types increased pH with increasing rate. The two substrates in general responded similarly to S and lime amendments, although there were some significant effects and interactions caused by substrate type. Ammonium-N and NO3-N both decreased exponentially with increasing substrate pH, whereas water-extractable phosphorus decreased linearly with increasing pH. Water-extractable potassium, calcium, magnesium, and sodium responded quadratically to increasing pH by initially decreasing and then increasing. The micronutrients boron and iron decreased with increasing pH, whereas DTPA extractions of manganese, zinc, and copper initially increased and then decreased over the range of observed pH.

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Annual vinca [Catharanthus roseus (L.) G. Don ‘Peppermint Cooler’] plugs were transplanted to containers filled with Douglas fir [Pseudotsuga menziesii (Mirbel) Franco] bark (DFB) in May and June 2005 (Expts. 1 and 2, respectively). Treatments were arranged in a 2 × 3 factorial with two DFB ages (fresh and aged) and three micronutrient sources (DFB alone, 10% by volume yard debris compost, or 0.9 kg·m−3 Micromax fertilizer). Plants were measured for shoot dry weight and foliar color. Substrate and foliar samples of each plant were analyzed for 13 essential macro- and micronutrients plus substrate pH and EC. Douglas fir bark alone appears to provide sufficient micronutrients for annual vinca grown at pH 4.7 to 5.7 over a 2-month period. In Expt. 1 there were no differences in shoot dry weight or foliar color regardless of DFB age or micronutrient source. At the end of Expt. 2, plants in aged DFB were larger than those in fresh DFB, but differences were primarily the result of nitrogen availability. None of the treatments developed color symptoms that could be associated with micronutrient deficiency. Micronutrient availability in DFB should be considered in container fertilizer management plans.

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A 1-year survey on the chemical and physical properties of Douglas fir [Pseudotsuga menziesii (Mirbel) Franco] bark was conducted with the following objectives: 1) to document baseline chemical and physical properties of Douglas fir bark (DFB) that have relevance to production of container plants; 2) to determine the effect of DFB age on its chemical and physical properties; and 3) to document the consistency of those properties throughout the year. In June, August, October, and Dec. 2005, and February and May 2006, fresh and aged DFB samples were collected from two primary DFB suppliers (bark sources) for Oregon nurseries: source A offers a bark screened to 0.95 cm or less (fine) and source B screened to 2.2 cm or less (coarse). Samples were analyzed for pH, electrical conductivity (EC), essential plant macro- and micronutrients, bulk density, particle size distribution, and substrate moisture characteristic curves. Air space (AS), container capacity (CC), and solids were determined as a percent of container volume. Nonamended fresh and aged DFB contains appreciable extractable amounts of all measured plant macro- and micronutrients, except N. In general, the aging process reduced pH; and increased EC, and extractability of phosphorous, calcium, magnesium, boron, iron, and aluminum. Uniformity of DFB chemical properties throughout the year was affected by bark source and less so by age. In terms of physical properties, aged DFB had lower AS and higher CC compared with fresh DFB. Average differences in AS and CC between fresh and aged DFB within a source were 8% or less. Similar to chemical properties, uniformity of DFB physical properties was more affected by bark source than age.

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The objective of this study was to determine if there are growth differences in geranium (Pelargonium ×hortorum ‘Maverick Red’) produced in fresh or aged douglas fir (Pseudotsuga menziesii) bark (DFB). A second objective was to document nitrogen (N) immobilization and decomposition rates of fresh and aged DFB to better understand the cause of growth differences. A series of experiments to measure plant response, N draw-down index (NDI), and percentage of cumulative carbon (C) loss were conducted on fresh and aged DFB. Geranium plugs were transplanted to containers filled with fresh or aged DFB. Treatments were arranged in a 2 × 3 factorial with two DFB ages (fresh and aged) and three N fertilizer rates (200, 300, and 400 mg·L−1). Plant growth was affected by DFB age in that geraniums were smaller when grown in fresh DFB. N draw-down analysis demonstrated that a large fraction of N in solution was immobilized in fresh and aged DFB. Carbon loss, measured as a gauge of bark decomposition, was not affected by N rate or bark type. Similarities in C loss between fresh and aged DFB agree with the similar N immobilization potential (NDI) in the two materials.

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