While biochar and manure can provide considerable benefits to soil properties, how these amendments may alter soil microbial activity and decomposition processes remains unknown. In a split-split-split-plot experiment, we amended a sandy loam soil with three rates of manure (whole plot; 0, 3, 9 Mg ha(-1)) and biochar (split-plot; 0, 2.5, 10 Mg ha(-1)), and installed three species of wood stakes (split-split-split plot; triploid poplar, Populus tomentosa Carr.; trembling aspen, Populus tremuloides Michx.; and loblolly pine, Pinus taeda L.) on the soil surface and in the mineral soil (split-split plot) to serve as a substrate for microbial degradation. Wood stakes were sampled 3 years after installation to assess decomposition rates (mass loss), and changes in wood carbon (C) and nitrogen (N). In addition, soil extracellular enzyme activities at the 0-20 cm depth were examined. Biochar alone, especially 10 Mg ha(-1), increased wood stake decomposition and moisture content on the soil surface and in the mineral soil. Manure at the rate of 9 Mg ha(-1) increased soil N-acetyl-beta-D-glucosaminidase, alpha-glucosidase, and aryl sulfatase activities by 91%, 17%, and 48% respectively. Because of the synergistic benefits of biochar and manure, we suggest that, in this climatic regime and soil texture, 10 Mg ha(-1 )biochar can be used for soil C sequestration and soil quality improvement, and 9 Mg ha(-1) manure can be used in combination with biochar to build soil organic matter in plantations.
