The Influence of Storage Time and Lime and Peatmoss Amendments On Pine Tree Substrate pH

This study was conducted to determine how pine tree substrate (PTS) pH was affected by storage time and lime and peatmoss amendments.  PTS was manufactured (April 2009) from freshly harvested loblolly pine trees (Pinus taeda L.), chipped, and hammermilled to two sizes, 4.76 mm, and 15.88 mm; the former substrate was unamended and the latter substrate was amended with 25% peatmoss (v/v, PTSP).  The PTS and PTSP substrates were amended with dolomitic limestone at rates of 0, 1, 2, 4, or 6 kg·m^-3.  Substrates were placed in 0.08 m³ perforated plastic storage bags and stored on shelves in an open shed in Blacksburg, Virginia.  Substrates were subsampled at 0, 42, 84, 168 and 270 days.  For all days and all lime rates, PTS had higher pH values than the corresponding PTSP treatments due to the acidifying effect of peatmoss.  For each sampling time, PTS pH values increased with increasing lime rate, with the largest increases occurring between 0 and 1 kg·m^-3 lime addition. For PTSP, there were relatively large pH increases with the incremental additions of lime, except between 4 and 6kg·m^-3.  PTS pH values for the first sampling date ranged from 5.8 to 6.6 (for 0 to 6 kg·m^-3 lime) and for PTSP from 5.2 to 6.6 (for 0 to 6 kg·m^-3 lime).  From the first sampling day to day 42, pH values decreased in all lime and substrate treatments.  However, by day 84, pH values for all treatments with lime addition had increased to values equal to or higher than those found at the first sampling date.  pH values for all treatments remained relatively constant from day 84 to day 168.  By day 270, pH values of all limed PTS treatments were similar to first sampling values, while the pH of unlimed PTS decreased from 5.8 to 5.0.  pH values for PTSP over 270 days were lower than the first sampling date, except for the 6 kg·m^-3 lime rate treatment.  After 270 days, PTSP pH for the unlimed treatment decreased 1.2 units, whereas the decrease for the 4 kg treatment was 0.2 units.  Results of this study show that a lime rate of 1 kg·m^-3 is sufficient to maintain PTS pH at or above 5.8 under storage conditions for at least 270 days. A lime rate of 4 to 6 kg·m^-3 is needed to maintain a pH value of 5.8 or higher for PTS amended with peatmoss.