Effect of soil moisture on soil compaction during skidding operations in poplar plantation

Abstract

ABSTRACT Poplar plantations have been widely practiced in the coastal area of the Caspian Sea in northern Iran. In this research, soil compaction following logging operations carried out by wheeled cable skidder was investigated in two poplar plantations with different characteristics including moist soil and dry soil. The soil gravimetric moisture content (MC) in the dry site ranged from 13% to 14.4%, while in the moist site it ranged from 30.5% to 34.6%. The mineral soil samples were collected from the skid trails in both sites. The impact of skidding operations on soil layers (soil depth, SD) was examined by measuring rut depth (RD), penetration resistance (PR), bulk density (BD), and total porosity (TP) at five traffic intensities (TI). Results indicated that MC and TI had a significant effect on RD, PR, BD, and TP; however, SD had a significant effect on PR and BD. The values of BD were significantly higher in the moist site than in the dry site, while the values of PR and TP were significantly higher in the dry site than in the moist site. The RD in the moist site (11.7 cm) was 1.65 times more than RD in the dry site (7.1 cm) after one pass where a pass was defined as one empty and one loaded trip over a spot. The differences between BD after 10 and 15 passes were not significant on the dry site, but significant in the moist site. We concluded that skidding operations should be conducted when soil conditions are dry.