A pulse method for studying effects of dead‐end pores, slow equilibration and soil structure on diffusion of solutes in soil

Summary A model is described for solute diffusion in an aggregated medium in which a proportion of the water‐filled pores are connected to a continuous pore network by narrow channels through which the diffusing ion can move only slowly. The experimental conditions for detecting departure from normal diffusion behaviour are discussed. A pulse technique for measuring the selfdiffision coefficient of 36Cl in both undisturbed and repacked soil samples at various moisture contents is described. No evidence of slow exchange between freely and slowly accessible pores was obtained. The self‐diffusion coefficients in large undisturbed peds were somewhat greater than in repacked sieved samples at the same volumetric moisture content.