Chemical and physical properties of Douglas fir bark relevant to the production of container plants

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.