EFFECTS OF MECHANICAL CONTAINER-FILLING METHODS ON TEXTURE AND WATER-RETENTION OF PEAT GROWTH MEDIA

Two commercial products of growth media made of light, low-humified Sp hagnum peat were used to determine how six different container-filling treatments with a mechanical filling machine affect the particle-size distribution and water-retention characteristics of peat. It was show n that, in particular, the feeding screw conveyor in the filling machi ne used broke down the peat particles, resulting in a significant incr ease in the proportion of <1 mm particles. The water retention and shr inkage measured at desorption of the peat media were also found to cha nge due to container filling, but these changes were relatively slight . However, depending on the peat product, reduction in particle size a ccompanied by heavy compaction can yield a marked increase in water re tention, especially under wet conditions (at > -1 kPa matric potential s), and correspondingly, decreased air-filled porosity. Consequently, in plant culturing heavy mechanical methods of container filling can c ause potential risk of restricted aeration to roots. These results sug gest a need to develop gentler filling machines without screw conveyor s.