CLAY FILM EFFECTS ON ION-TRANSPORT IN SOIL

Soil nutrient retention and groundwater contamination are concerns in agricultural and environmental science. Preferential flow can either i ncrease or decrease the residence time of solutes in soil, depending o n the location of solutes relative to macropores. Clay films that form on ped surfaces may affect ion transport and retention during flow ev ents. These possibilities were investigated by studying the transport of strontium and bromide in soil columns with artificial macropores th at had been coated with clay films. The disappearance of Sr and Br fro nt solution percolating through the pore and subsequent lateral transp ort into a soil matrix were measured. Clay films retarded Sr removal f rom solution, thus reducing Sr retention by the soil matrix. Br was un iformly distributed laterally across the soil matrix (5.2-cm(2)) 1 day after the flow event, whereas 30 days were required for Sr to become uniformly distributed. In a second phase, leaching of SrBr2 from the s oil into the pore was retarded by clay films. A slow flow rate, 0.25 p ore volumes per min, was more effective in leaching solutes from the s oil matrix than a faster flow rate of 0.51 pore volumes per min. Leach ing loss of Br was about twice that of Sr.