Subsoils in Prince Edward Island have poor chemical and often physical quality for root growth that may present a barrier to development of alfalfa (Medicago sativa L.). This study was conducted to characterise the response or benefit, on soil properties and alfalfa growth, of chemical amelioration and loosening of the subsoil. In 1987, the following three treatments were imposed on an acidic, fine sandy loam, Humo-Ferric Podzol: control (no subsoiling or lime), subsoiling alone, and subsoiling plus lime (5 Mg ha−1 dry CaCO3) mixed into the subsoil. The subsoiler was a Wye Double-Digger, a combined plough and rotary cultivator that facilitated the mixing of lime into the soil over the 230–480 mm depth. Management of the 0–200 mm soil depth was the same for all treatments. Growth of alfalfa and change in soil properties were monitored over time. In 2 of 4 yr (1991–1994), alfalfa yield was significantly (P < 0.05) increased by the subsoil plus lime treatment, compared with subsoiling alone or the control. Yield increases were related to periods of low growing season precipitation. Subsoil amelioration increased alfalfa root penetration (by 90 mm) and reduced leaf Mn concentration. Over an 8-yr period (1987–1994), soil exchangeable Ca was increased over fourfold, while exchangeable Al was decreased threefold in the ameliorated subsoil, compared with the control. Soil pH (in water) was increased from 4.8 to near 6.0. There was some evidence that liming of the topsoil improved the subsoil chemistry over time. Bulk density and penetrometer resistance contours, measured over time, indicated that the soil loosening effect was sustained throughout the soil profile over the duration of the study. Soil biological properties were not changed by the subsoil treatments. Key words: Subsoil acidity, podzol, lime, deep placement, alfalfa (Medicago sativa L.), cool-humid climate