Technical Abstract: Biochars have received increasing attention in recent years for a large-scale soil amendment to improve soil fertility, immobilize contaminants, and to serve as a recalcitrant carbon stock. Information is currently lacking in factors controlling the sorption capacity of manure-derived biochars. In this study, sorption isotherms for deisopropylatrazine, a stable metabolite of widely applied herbicide atrazine, were obtained in acidic aqueous media (pH 5.5) for broiler litter-derived biochars formed by pyrolysis at 350 and 700 degrees C with and without steam activation at 800 degrees C. An increase in Freundlich distribution coefficient (KF) and isotherm nonlinearity (nF) was observed with pyrolysis temperature and steam-activation, suggesting that the surface area and aromaticity (degree of carbonization) are the factors controlling the sorption capacity of chars at low surface coverage. At high surface coverage, the isotherms became increasingly linear, suggesting sorption on noncarbonized fraction of biochars. In binary-solute experiments, sorption of deisopropylatrazine was significantly diminished by CuII, further suggesting the predominance of surface adsorption mechanism at low surface coverage of biochars.