Abstract
Differences in the filling amount of substrates in container can influence severely on the soil physical properties and crop growth. This research was conducted to secure the fundamental informations related to the changes in soil physical properties as influenced by the filling amount of coir dust-based substrates in container. For the experiment, three substrates were formulated by blending coir dust (CD) with expanded rice hull (CD+ERH, 8:2, v/v), carbonized rice hull (CD+CRH, 6:4, v/v) or ground and aged pine bark (CD+GAPB, 8:2, v/v). Based on the optimum bulk density, the amount of substrates filled in 347.5mL aluminum cylinder were adjusted to 90, 100, 110, 120, and 130%. Then the changes in total porosity (TP), container capacity (CC), and air-filled porosity (AFP) by various filling amounts were measured. The TP decreased linearly in CD+ERH and CD+GAPB and quadratically in CD+CRH as the filling amounts of the media increased from 90% to 130%. The CC in CD+ERH and CD+GAPB media increased as the filling amount increased from 90% to 120%, then decreased in 130%, showing quadratic change. The CC in CD+CRH was the highest in 90% filling amount and decreased gradually as the filling amount of root medea increased. The AFPs in CD+ERH and CD+GAPB media were 38 and 37%, respectively in 90% filling amount and they decreased drastically until 110% filling, then gradually in 120 and 130% filling amount showing the quadratic changes. The AFP of CD+CRH at 90% filling amount was 22% and it decreased as the filling amount increased until 130%, showing linear change. These results indicate that the increase in filling amount of substrates influenced more severely the AFP than CC, and careful consideration on container filling is required to provide a better root condition thus maximize crop growth.
