AbstractMisciple displacement studies were conducted in the laboratory to determine the dispersion and diffusion coefficients of nitrate and bicarbonate ions in capillary tubes, sand and soil columns. Necessary mathematical equations used for the evaluation of the dispersion coefficients are discussed. The dispersion coefficients evaluated with use of two different models are compared, particularly with reference to their velocity dependence. The values of the dispersion coefficients (D1and D2) and molecular diffusion coefficients (D01and D02) were found to be several times higher in the Kirkham and Powers' moving coordinate model than those in a probability model.