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Samples of soil, mulch, and the soil/mulch interface zone were collected from commercial highbush blueberry (Vaccinium corymbosum L.) fields typical in their use of mulch under Arkansas conditions. Mulches included J-year-old hardwood sawdust, 5-year-old hardwood sawdust, and 1-year-old pine needle mulch. Herbicide adsorption (Kd values) of the samples was determined for diuron, terbacil, and simazine. The soils, mulches, and interfaces adsorbed nearly 10 times as much diuron and more than twice as much simazine as terbacil. Adsorption of the herbicides was three to five times greater to the mulches than to the soils. Adsorption was significantly correlated with the organic matter content of the mulch. Adsorption was not related to herbicide solubility. Although no statistical differences were found among the three mulch materials, adsorption coefficients (Kd values) were numerically lower for each chemical on the 5-year-old hardwood mulch than on the 1-year-old hardwood or pine mulch. Chemical names used: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron); 3-tert-butyl-5-chloro-6-methyluracil (terbacil); 2-chloro-4,6-bis(ethylamine)-s-triazine (simazine).