The agricultural soils of the Happy Valley-Goose Bay (HV-GB) region of Newfoundland and Labrador, Canada are Podzols that are converted from boreal forest and have limited productivity due to their sandy texture, acidity, low soil organic matter (SOM), cation-exchange capacity (CEC), and water and nutrient retention capacity. Although numerous studies advocate biochar for mitigating soil quality problems and enhancing agronomic productivity, there is limited information on managing biochar for boosting the productivity of Podzols under newly converted agricultural lands. A 5 year experiment evaluated the impact of eight biochar rates (0–80 Mg C·ha⁻¹) on soil properties including SOM, CEC, and availability of plant nutrients and metals in agricultural soils of HV-GB. Both immediate and long-term impacts were thus assessed. Biochar generally improved soil fertility indicators. Although the largest rates (40 and 80 Mg C·ha⁻¹) led to the greatest changes, significant changes were also found with rates as low as 10 Mg C·ha⁻¹. Increasing biochar rates had diminishing returns for quality parameters of soil. The impact of biochar decreased with time after application, but the largest rate led to longer lasting effects. Although biochar was incorporated in topsoil, its effects were also measurable in the subsoil, albeit with a temporal delay, usually of 1 year. Thus, given the diminishing returns of increasing biochar rates, and that beneficial effects diminish over years, it is advisable that biochar be added in smaller amounts immediately after conversion, as little as 10 Mg C·ha⁻¹, with regular supplementation as needed.