Effect of Storage Time On Pine Tree Substrate Bulk Density, Particle Size and Cation Exchange Capacity

Pine tree substrate (PTS) is a relatively new container substrate that can serve as a replacement for pine bark and peat.  However, there is relatively little research documenting the physical and chemical property changes that occur in PTS during storage with and without amendments.  The objective of this work was to determine how storage time of PTS with and without lime and peat amendments influenced substrate bulk density, particle size distribution, and cation exchange capacity (CEC).  PTS was manufactured (April 2009) from freshly harvested loblolly pine trees (Pinus taeda L.), chipped and hammermilled to two sizes, 4.7 mm without peat amendment (PTS), and 15.8 mm amended with 25% peat (v/v, PTSP).  A peat /perlite (4:1 v/v, PL) treatment served as a control.  Substrates were amended with dolomitic limestone at 0 or 1 kg·m^-3 for PTS, 0 or 4 kg·m^-3 for PTSP, and 6 kg·m^-3 for PL.  Substrates were placed in 0.08 m³ plastic bags and stored on shelves in an open shed in Blacksburg, Virginia and subsampled at 1, 168, and 365 days.  Day 1 bulk densities (PTS 0.11 g·cc^-1, PTSP 0.12 g·cc^-1, PL 0.11 g·cc^-1) remained unchanged throughout the 365 days, with or without lime addition.   Particle size distribution remained the same for PTS with no lime over 365 days, but for PTS with 1 kg·m^-3 lime there was an increase in medium size particles (0.5 to 2 mm) by day 168 with no change thereafter.  For PTSP without lime, there was a decrease in medium size particles and an increase in fine particles (< 0.5 mm) by day 168 and no change thereafter.  For PTSP with 4 kg·m^-3 lime, there was no change in distribution throughout the experiment.  For PL, there was a decrease in coarse and medium size particles and an increase in fine size particles by 6 months and no significant change thereafter.  CEC values (PTS 2 cmol·L^-1, PTSP 5 cmol·L^-1, PL 13 cmol·L^-1) were the same throughout the experiment for all of the substrate treatments, with or without lime. The physical and chemical characteristics of PTS and PTSP monitored in this study remained relatively stable over one year of storage.  Particle size changes observed in PTS with 1 kg·m^-3 lime and PTSP with no lime occurred within the first 6 months and had no measurable effect on bulk density or CEC.