TILLAGE OF COMPACTED HAUL ROADS AND LANDINGS IN THE BOREAL FORESTS OFALBERTA, CANADA

Ten temporary haul roads and landings in west-central Alberta were til led with a winged subsoiler specifically designed for tilling compacte d forest soils. Surface soil had been removed from all sites during co nstruction, and spread over three of the four landings prior to tillag e. Soil bulk density at the 0-10, 10-20, and 20-30 cm depths, and clod size distribution at the 0-30 cm depth were measured immediately afte r tillage. Bulk density of undisturbed and compacted (untilled) soil w as also measured. Mean bulk density of compacted soil in haul roads wa s significantly greater than the bulk density of undisturbed soil, but not for landings. Tillage significantly reduced mean bulk density on three haul roads and two landings; subsurface soil was relatively dry at these sites. Most soils were difficult to fracture into small clods because these weakly aggregated soils were severely remoulded and com pacted by equipment, particularly logging trucks operating on the haul roads. The degraded soil was massive and the strength of the surface soil layers was generally much higher than was the strength of lower s oil layers; this resulted in the subsoil deforming around the wings of the subsoiler rather than fracturing the surface soil. Fracturing of compacted soil into small clods was apparently enhanced by at least 2 years of frost action. The winged subsoiler was only moderately effect ive at fracturing recently compacted soil because of an often high soi l water content, but it was observed that sites where soil was broken into large clods was loosened by frost action the following winter. Al ternative methods of tilling compacted soil that insure soil fracturin g over a wider range of soil water contents are needed for loosening c ompacted soil in northern boreal forests.