Biochar is being promoted as a source of carbon (C) sequestration and soil amendment, improving soil properties.  Yet the impact on soil C is still not well understood, with some biochars promoting native soil C loss. More information is needed on the influence of biochar on soils under different land managements. The objective of this study is to determine the effect of increasing loading rates of two biochars with different feedstock characteristics on C mineralization in different textured soils and land uses.  Loading rates of southern pine and cottonwood biochars at 1, 3, 6, and 10%, were added to sandy and clayey soils with differing fertility regimes, unfertilized forest vs. row crop. Six month results show sandy forested soil having significantly more C mineralization when 10% biochar is added, compared to other rates and sandy cropped soil, with up to 3 times more C was lost than in the cropped soil. Cotton biochar had significantly more mineralization than pine biochar in the 6 and 10% loading rates in the sandy forested soil while only 10% was different in the clayey forested soil. No differences were found in the cropped soils between biochars or soil texture. All biochar loading rates, except the lowest, show increased C mineralization.