Effect of soil compaction on hydraulic properties of two loess soils in China

Soil compaction affects hydraulic properties, and thus can lead to soil degradation and other adverse effects on environmental quality. This study evaluates the effects of three levels of compaction on the hydraulic properties of two silty loam soils from the Loess Plateau, China. Undisturbed soil cores were collected from the surface (0-5 cm) and subsurface (10-15 cm) layers at sites in Mizhi and Heyang in Shaanxi Province. The three levels of soil compaction were set by increasing soil bulk density by 0% (CO), 10% (C1) and 20% (C2) through compression and hammering in the laboratory. Soil water retention curves were then determined, and both saturated hydraulic conducitivity (K-s) and unsaturated hydraulic conductivity were estimated for all of the samples using standard suction apparatus, a constant head method and the hot-air method, respectively. The high level of compaction (C2) significantly changed the water retention curves of both the surface and subsurface layers of the Heyang soil, and both levels of compaction (C1 and C2) changed the curves of the two layers from the Mizhi site. However, the effects of compaction on the two soils were only pronounced below water tensions of 100 kPa. Saturated hydraulic conductivities (K-s) were significantly reduced by the highest compaction level for both sampled layers of the Heyang soil, but no difference was observed in this respect between the CO and C I treatments. K-s values decreased with increasing soil compaction for both layers of the Mizhi soil. Unsaturated hydraulic conductivities were not affected by soil compaction levels in the measured water volume ratio range, and the values obtained were two to five orders of magnitude higher for the Mizhi soil than for the Heyang soil. The results indicate that soil compaction could strongly influence, in different ways, the hydraulic properties of the two soils. (c) 2005 Elsevier B.V. All rights reserved.