2017 ASHS Annual Conference

Pine bark is one of the most commonly used horticultural substrates, and may be used as a fresh, aged, or composted product. While aged pine bark is most commonly used, fresh PB may also be used successfully, but there is little research investigating the differences between bark of specific ages. A twelve-month study was initiated to better understand the effects of aging and pile management on pine bark substrates. Fresh pine bark was processed and the fines were placed in three pile replications of 191 cubic meters each. Beginning at time 0 and every 4 to 5 weeks for a period of twelve months, stratified subsamples were taken from each pile and tested for physical, hydrologic, and chemical properties. Physical properties include pile volume, temperature, particle size distribution, total porosity, container capacity, air space, bulk density, white wood content, and color. Hydrologic properties include wettability, saturated hydraulic conductivity, moisture retention curves, models for nursery containers, and pore fraction volume analysis. Chemical properties include pH, EC, pH buffering capacity, CEC, AEC, plant available nutrients, liming, C:N ratio, lignocellulose content, and seedling germination tests. We observed that bark managed under these conditions stabilized around 6 months of aging, as shown by decreases in average and stratified pile temperatures after an initial increase and 4 month thermophilic phase, color darkening, decreased white wood content, a shift to higher percentages of fine particles in the same total pore volume, an increase in container capacity, and subsequent decrease in air space and an increase in bulk density. These changes in particle size and physical properties in turn influenced hydrologic and chemical properties, which may have an impact on irrigation and fertilization regimes. The data generated from this research can hopefully improve the understanding, product consistency, and usability of pine bark substrates of different ages.