Technical Abstract: Soils of the US Great Plains are strongly affected by climate and contain enormous soil organic carbon (SOC) and soil organic nitrogen stocks (SON) that are likely vulnerable to predicted climate and land-use change. Climate change scenarios predict a 2.2-3.6°C (4-6.5°F) increase in temperature across most of the United States by 2040-2059 and increased variability in precipitation. Land in CRP (conservation reserve program) is currently being converted to cropped systems due to biofuel demand. Here, we evaluate climatic drivers and soil properties on C and N storage under different land-uses (cropped, CRP, and native) using paired pedons. Soil C stocks were strongly related to temperature but not moisture gradients, with the greatest SOC in cool climates. Soil cation exchange capacity and bulk density were important covariates in explaining SOC content. SOC and SON stocks were significantly greater under CRP compared to cropland in the surface 0-5 and 0-10 cm depths. The predicted temperature increase on SOC and SON stocks within the 1.3 x 10¹4 ha within the US Great Plains, along with land use changes from CRP to cropped agriculture, may significantly decrease the SOC sink or result in the loss of previously stored SOC as CO2.