Soil degradation by tillage movement

Soil movement by tillage implements is an often overlooked but significant cause of soil degradation in the steep cropland of the Pacific Northwest, USA. Evidence is seen in ridgetops devoid of topsoil and in near-vertical embankments at the lower boundary of steep fields. Traditionally, the moldboard plow was the principal implement used for the first tillage operation after harvest, with the furrow turned downslope on steep slopes because of power requirements. Experiments were conducted to quantify soil displacement with the moldboard plow, and a relationship was developed between land slope and soil movement. Deposition was measured at the lower boundary of fields where water erosion was not involved. Calculated soil movement assuming typical tillage practices was approximated by the measured deposition. The results emphasize the magnitude and importance of tillage movement in land degradation in the region. Unless corrective measures are taken, exposed subsoil materials on ridgetops and other areas will be translocated to cover productive downslope topsoil.