Biochar application on agricultural soils is an interesting emerging technology with promising potential for long-term carbon storage and the enhancement of soil fertility. The effect of a biochar compost mixture with and without standard NPK fertilizer was assessed to determine the effects on the growth of cabbage over 3 yr at two locations. Field trials were established at the Holland Marsh and Simcoe Research Station in Ontario. The main purpose of this study was to determine the effect of biochar soil amendment on cabbage yield and quality. Biochar (a blend of 1:1 composted duck manure and biochar based on dry weight) was applied at rates of 0.6 and 2.4 kg m^-2 with and without standard NPK fertilizer and compared with compost at the rate of 1.2 kg m^-2, which was the rate applied with the high rate of biochar. The biochar used was somewhat alkaline (pH 8.1) and increased the pH (>0.5) of the top 0–15 cm of the soil. It also had a high cation-exchange capacity (CEC > 25) and contained elevated levels of some trace metals and exchangeable cations (K, Ca, and Mg) in comparison to the untreated soil. None of the biochar or compost treatments increased yield compared with the nonamended check at either location. Treatments that included the standard NPK fertilizer resulted in the highest yields.