2018 ASHS Annual Conference

Aged pine bark is the one of the most common organic substrate components in the U.S., with bark from loblolly or longleaf pines being the most prominent in the southeastern U.S. Aging is a process in which the bark is piled on the ground in windrows and allowed to age for a period of time, usually six months to one year. Aging time can vary between suppliers, or even for the same supplier, based on factors such as space shortages, product demand, or preference. A long-term study was implemented to quantify the changes in the hydrological properties of longleaf pine bark over the course of twelve months of aging. The hydration efficiency of the aged pine bark samples were assessed by measuring the water retention after 10 hydration events (simulated irrigation's). Bark samples were analyzed at 50% moisture content (moist) and at a 25% moisture content (dry). At 50% moisture content, we found that bark hydrated similarly for all ages. This means that after the first irrigation event, bark was wetted to its maximum capacity (reached container capacity). At 25% moisture content all samples showed less water uptake than at 50% moisture content, regardless of sample date. At 25% moisture content fresh bark (month 0) never hydrated (reached container capacity). At month 6 the bark was able to reach its maximum hydration potential after five irrigation events. At month 12 it reverted back to a more hydrophobic state and never reached full hydration. In regards to water percolation, month 0 bark (fresh) had a water flow rate of 119 cm/min, month 6 bark had a flow rate of 80 cm/min and month 12 bark was recorded at 55 cm/min. This is likely due to the reductions in particle size over time resulting from mechanical breakdown by turning and microbial degradation, as well as an increase in sand content. The smaller particles result in smaller pore sizes and an increased bulk density. The decreased percolation of older bark compared to fresher bark would make significant changes to irrigation practices on a nursery especially if bark of different ages was being used in the production system.