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Title:   Author  item
                                            Altland, Jamesitem
                                            OWEN, JIM - OREGON STATE UNIVERSITY
  Submitted to: HortScience
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/8/2007
                                    Publication  Date: 4/1/2008
                                    Citation: Altland, J.E., Owen, J. 2008. Container Height and Douglas Fir Bark Texture Affect Substrate Physical Properties. HortScience. 43:505-508.Interpretive Summary: Physical properties of container nursery substrates are measured to assess their porosity, drainage, and general suitability for growing commercial nursery crops.  Physical properties are measured routinely using a device known as a porometer.  While this device provides useful information on substrate physical properties, it does not provide a complete picture of how air and water are held within a substrate from the bottom to the top of a container.
Our research documented the changes in air and water from the container bottom to the top.  This has important implications in how substrate physical properties are determine and interpreted.  This research primarily reminds other scientists and university extension agents involved in measuring physical properties, that the height of the vessel in which measurements are made will have a profound impact on final measurements.  It also sheds light on the fact that container substrates are not uniformly subjected to equal water, temperature, and biological activity within a container.  Due to strata in available water from the container bottom to the surface, differences in the biology and chemistry of nursery substrates is also likely.  This research suggests that studies on container substrate chemistry and biology might be more accurate if assessed in strata instead of assuming that substrate throughout the entire container is uniform.
                                Technical Abstract: A study was conducted to quantify the effect of substrate texture on water holding capacity of douglas fir [Pseudotsuga menziesii (Mirb.) Franco] bark (DFB) in containers of varying height.  Increasing container height resulted in a linear decrease in CC and a linear increase in AS.  Fine texture DFB bulk density (Db) increased 18% with increasing container height, whereas Db of medium texture DFB was unaffected.  Water holding capacity decreased 20% and 42% in medium and fine textured DFB, respectively, with increasing container height from 0 to 15.2 cm.  A second study was conducted to investigate water distribution in a 15.2 cm tall container for a given substrate texture.  Medium (< 2.2 cm) and fine (< 0.9 cm) DFB were packed into 7.6 cm i.d. aluminum cores 3.8, 7.6, and 15.2 cm tall to determine container capacity (CC) and air space (AS) at varying container heights.  In addition, polyvinyl chloride (PVC) cores (15.2 cm tall by 7.6 cm i.d.) were packed with the same substrates, drained to CC, frozen, and sawed into 2.5 cm sections to determine water holding capacity at each height.  Substrate texture increased the amount of water  throughout the container profile, but percent of total water for each strata remained similar.  Container height and plant size (i.e. transplant or salable), in relation to substrate texture, should be considerations when producing containerized crops. In addition, bark texture alters water holding capacity and water distribution within the container, ultimately affecting water management practices.


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