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.