A Study to Investigate the Effects of Aging and Pile Management on Processed Pine Bark

Aged pine bark is a commonly used substrate component in the southeast United States. Aging is a modified composting process in which bark is piled in windrows for a period of time, usually six months to one year. Aging time can vary between bark suppliers, or even for the same supplier. Recently, demand for fresh pine bark instead of aged has increased because of its lighter weight, resulting in cheaper transportation costs. Little research has been done to investigate the differences between bark of various ages, with discrepancies in the literature about the effect aging has on nitrogen immobilization, fertilizer rates, irrigation, and potential toxicity. In addition to a lack of information on the differences between aged and fresh pine bark, there is no information regarding the effects of processing, material handling, or pile management on the end product quality. A long term study was initiated to better understand the effects of aging and pile management on pine bark substrates. The study is being conducted at TH Blue, Inc., a pine bark supplier in Eagle Springs, North Carolina. Fresh pine bark was processed and the fines were placed in three piles (replications) of 250 cubic yards each. Beginning at time 0 and every 4 to 5 weeks for a period of twelve months, stratified subsamples are taken from each pile at three different heights (top, middle, and bottom) at depths of 1’-4’ to account for variations in pile depth and height. The stratified subsamples are mixed into one composite sample for each pile replication to test the physical, chemical, and biological properties of the pine bark. Physical properties include pile dimensions, temperature, particle size distribution, total porosity, container capacity, air space, bulk density, wettability, white wood content, color, and thermal imaging. Chemical properties include pH, EC, total elemental analysis, and CEC. Biological properties include incubation experiments to determine nitrogen immobilization/mineralization, and seedling germination tests. With the conclusion of this study, the data generated can hopefully improve the consistency and usability of pine bark substrates, and provide guidelines for bark processors for pile management.