EFFECT OF HIGH-AXLE LOAD TRAFFIC ON SUBSOIL PHYSICAL-PROPERTIES AND CROP YIELDS IN THE PACIFIC-NORTHWEST USA

Cultural practices for winter wheat production in the Pacific Northwest USA include rotations with spring crops. These cultural practices result in heavy wheel traffic (greater-than-or-equal-to 9 Mg per axle) during wet soil conditions, which could result in serious soil compaction. A field experiment was initiated in the spring of 1986 near Moscow, Idaho, USA, on a silt loam soil to determine the effect of heavy axle loads On subsoil physical properties and crop yields. Compaction treatments consisted of axle loads of < 5 (check ), 10, and 20 Mg applied track-to-track four times at experiment initiation. Bulk density and impedance within the subsoil were increased by the 10 and 20 Mg loads to a depth of 0.75 m. The effects of the one-time high axle load traffic persisted after 3 years. Crop yields were not significantly reduced by the soil physical conditions resulting from the 10 Mg load. Compaction resulting from the 0 Mg load limited root growth and reduced subsoil water extraction.