Twelve farmers from Kent County in southwestern Ontario co-operated in this study to observe the effect of subsoiling on corn yields and soil conditions. Problem: This study focused on the subsoiler performance in the soil layer below the plow depth (ie. about 15 to 30 cm below ground surface). This region within the soil profile is where compaction can occur. Soil compaction may include one or more of these conditions: degraded soil structure, reduced size, abundance and continuity of vertical cracks and pores, smearing, increased soil bulk density, layering, and, altered rooting pattern and depth. These conditions tend to reduce the soils' ability to produce abundant crops due to deterioration of root zone quality. Soil permeability is also reduced and this results in increased runoff and erosion. A previous Can-Ag compaction study indicated that about 50 to 70 percent of the clay to clay loam soils in several southwestern Ontario counties are affected. Of this total, about 25% are severely compacted and 75% are moderately affected resulting in crop yield reduction, increased soil erosion, and increased phosphorus loadings to the Great Lakes. Purpose: The purpose of the study was to evaluate the B.C. Sub-mulcher, a narrow shank subsoiler, pulled through corn rows at depths of 18 and 31 cm in June of 1988. Not only did we look at the soil and plant response to the subsoiling, but also to determine what other management practices may affect soil compaction and yields.