Biochar additions to soil can increase soil organic carbon (SOC) concentrations; however, minimal information is available on relationships with soil nitrogen (N) cycle. We hypothesized that biochar additions to sandy soils should be resistant to microbial mineralization in short-term studies but may prime organic carbon (OC) mineralization of fresh residue that promotes N immobilization. A laboratory pot incubation study was conducted with a Norfolk loamy sand (Fine-loamy, kaolinitic, thermic, Typic Kandiudult) mixed with pecan-shell biochar at rates of 0, 5, 10 and 20gkg⁻¹ and with 0 and 10gkg⁻¹ dried, ground switchgrass (Panicum virgatum L.). On days 25 and 67 of the incubation, all pots were leached with 1.2 to 1.3 pore volumes of deionized H₂O and the leachate NO₃–N, NH₄–N, and dissolved organic (DOC) concentrations were measured. Also cumulative soil CO₂ fluxes after days 25 and 67 were determined. Biochar alone and mixed with soil and switchgrass after 67days of incubation were characterized using Fourier transformed infrared spectroscopy (FT-IR). Mixing biochar with switchgrass after 67days caused a significant increase in SOC content while soil total nitrogen (TN) and leachate DOC concentrations showed mixed results. Biochar mineralization by itself was found to be minimal, but by days 25 and 67, soil with biochar and switchgrass exhibited higher cumulative CO₂ fluxes implying stimulation of switchgrass mineralization. Significant NO₃–N immobilization occurred after 25days in treatments with biochar + switchgrass; however, by day 67 the NO₃–N concentrations rebounded slightly. The FT-IR analysis revealed that switchgrass in the presence of biochar underwent some structural modifications. Biochar applications in the short-term can cause N immobilization resulting in temporary plant available NO₃–N concentration reductions.