Comparison of Sampling Methods Used to Evaluate Forest Soil Bulk Density

The objective of this study was to compare forest soil bulk density values obtained through conventional sampling methods such as the volumetric ring (VR: diameter 5 cm, length 10 cm) and paraffin sealed clod (PSC), with a variation of the VR, where rectangular boxes (RB) of four different dimensions were used. Sampling transects were established on a machine operating trail located in a beech (Fagus oriental is Lipsky) stand in Northern Iran. At each transect, three soil samples were collected at three different locations. Samples from different methods were spaced by a 50 cm distance to avoid direct interactions. The soil class of our study area was Combisols according to the WRB classification with a clay texture. Soil bulk density differed significantly between the three sampling methods. The lowest values were obtained with the RB (average 1.25 g cm(-3)), followed by the VR (average 1.40 g cm(-3)), and lastly the PSC (average 1.52 g cm(-3)). The values obtained with four variations of the RB method ranged from 1.22 to 1.28 g cm(-3) and were not found significantly different. When soil bulk density was calculated after the removal of the weight and volume of roots included in the samples, the values were determined to be higher than before but with the same range of magnitude. The lowest coefficient of variation was found for RB4 (CV=2.3%), while the highest values were observed for VR and RB1 (CV=5.7%).