Fig. 3. (A) Ratios of effective and molecular diffusion coefficients as determined in the field and in the laboratory on undisturbed soil cores from the same location. Data from Rolston et al. (1991), Jellick and Schnabel (1986), and Ball et al. (1994). (B) Ratios of effective and molecular diffusion coefficients as determined in the field and as estimated from soil porosity data according to Moldrup et al. (2000). Data were obtained with the surface chamber method (circles), single-well methods (diamonds), and an inter-well method (triangles).