Technical Abstract: The recent focus of biochar as a soil amendment for improving soil physical-chemical properties and carbon sequestration has revealed knowledge gaps in the research covering different feedstocks in various soil types. Biochars made from four feedstocks (wood pellets [Pseudotsuga menziesii], softwood bark [Pseudotsuga menziesii], switchgrass [Panicum virgatum] straw, anaerobic digester fiber) produced by pyrolysis at 500oC were evaluated for pH, cation exchange capacity, water holding capacity, elemental content, and C and N mineralization potentials in five soils. Soils were amended with four rates (0 9.8, 19.5 and 39.0 Mg ha-1) of the various biochars and evaluated under laboratory incubation. The C content of chars derived from the herbaceous feedstocks was 60 to 67% whereas that of the woody feedstocks was >75%. Biochars, despite their origin, raised the pH of all soil types 0.1 to 0.9 units with the greatest impact on a Quincy sand soil. The chars increased soil carbon and produced mixed results on water holding capacity dependent on soil and char. Nitrogen mineralization rates decreased in three of the five soils across all feedstocks with the remaining two soils showing various increases or no change from application of the switchgrass and anaerobic fiber derived chars. The biochar was stable in the soil after 225-d incubation; there was a significant correlation (r'90) between predicted and actual soil carbon after biochar additions regardless of feedstock or soil type. These differences were attributed to the biochar’s individual elemental and structural characteristics.