Biochar and hydrochars (HC) are emerging soil fertility amendments; however, their ability to improve fertility levels in soils possessing vastly different pedogenic characteristics has not been well investigated. In this study, several plant and manure biochars and two blended HC applied at 3.84 g/kg (ca.10 t/ha) were incubated in pots containing a highly fertile-Mollisol (Waukegan series; Sandy-skeletal, mixed, superactive, mesic Typic Hapludoll) and an infertile Entisol (Margate series; Siliceous, hyperthermic, Mollic Psammaquent). During the 124–125 day laboratory incubations, pots were leached four times with deionized H2O with the leachates analysed for the concentrations of dissolved phosphorus (DP) and potassium (DK). After the incubations, both soils were analysed for fertility characteristics (i.e. pH, cation-exchange capacity (CEC), and extractable P and K). In both soils after biochar additions, there were mixed pH and CEC responses. Both the Mollisol and Entisol treated with swine solid biochar had greater plant extractable P and K contents, which was reflective of the elevated P and K contents in the swine solid biochar. However, most biochars and HC additions to the Mollisol and Entisol had minimal impact on soil fertility characteristics indicating a low direct fertilization potential. These nutrient contents could be altered through feedstock blending to target a particular fertilizer requirement.