Substituting pine wood for pine bark affects physical properties of nursery substrates

Authors: Altland, James; Krause, Charles

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2012
Publication Date: 10/1/2012
Citation: Altland, J.E., Krause, C.R. 2012. Substituting pine wood for pine bark affects physical properties of nursery substrates. HortScience. 47(10):1499-1503.

Interpretive Summary: Pine bark is the primary potting component used in container production throughout the eastern United States. Most pine bark is generated in the southeastern United States by lumber and paper mills that harvest pine trees for their wood and sell off the bark for horticulture and other industries. Nurseries in northern states must import the pine bark from long distances, which is negatively affected by rising fuel prices. Furthermore, purchasing pine bark from this supply stream leaves the horticulture industry to depend on the volatile fluctuations in supply from the forest industry. The objective of this research was to determine if locally harvested pine trees (bark and wood) could be processed and used as a substitute for part or all of the pine bark fraction in nursery potting mixes typical of Ohio. The specific objective of this paper was to document the impact of pine wood on the physical properties of nursery substrates when used to replace 0, 50, or 100% of the pine bark fraction. Four nursery sites were selected from northern Ohio to participate in the research. Each nursery site produced three substrates unique to their site: their traditional substrate, their traditional substrate with 50% of the pine bark replaced with pine wood, and their traditional substrate with 100% of the pine bark replaced with pine wood. The pine wood material had a particle size distribution consistent with the pine bark used by the four nurseries. There was no consistent or predictable trend in measured physical properties by substituting pine bark with pine wood. All substrates at all nursery sites had physical properties that were considered acceptable for nursery crop production. Substitution of pine bark with pine wood did change the air space, water holding capacity, total porosity, bulk density, and available water for some, but not all, substrates. Using pine wood might require some growers to adjust their irrigation practices slightly, however, all substrates would be suitable for production nursery crops when judged solely by their physical properties.

Technical Abstract: Pine bark (PB) is currently imported from southern U.S. states to those in the upper Midwest and Northeast U.S. Alternatives to pine bark that are regionally abundant and sustainable are needed for nursery substrates. The objective of this research was to determine the influence of chipped and hammermilled pine trees (excluding branches and needles) on substrate physical properties when substituted partially or wholly for pine bark in substrates typical of Ohio. Four cooperating nursery sites, each with unique substrates comprised primarily of pine bark, were recruited to use pine wood as a substitute for 0%, 50%, or 100% of the pine bark fraction in their substrate. All other physical and chemical amendments used traditionally at each site were incorporated. Physical properties including particle size distribution (PSD), air space (AC), container capacity (CC), total porosity (TP), unavailable water (UAW), bulk density (Db), and moisture characteristic curves (MCC) were determined for each substrate at each cooperator site. Pine wood was generally more coarse than all but one of the PB materials used by the four cooperating sites. Amendment with PW did not have any consistent or predictable effect on AS, CC, TP, or Db of the resultant substrates. Pine wood had little identifiable effect on plotted MCC, although it reduced calculated easily available water in one substrate. It was concluded that substitution of PB with PW can result in changes to substrate physical properties that might lead to irrigation management changes, but none of these changes were considered negative or drastic enough to cause physical properties to be outside of acceptable ranges.