PREFERENTIAL SOLUTE TRANSPORT THROUGH MACROPORES IN LARGE UNDISTURBED SATURATED SOIL COLUMNS

Six large undisturbed soil columns (61 cm in length, 15 cm in diameter) were collected from three no-till and three conventional tillage field plots. The side walls of these columns were sealed with either plaster of paris or paraffin wax to eliminate wall effects. After these columns were saturated with CaSO4 (0.005 M), CaCl2 (0.005 M) was applied at the surface and the effluent was collected at the bottom. Effluent samples were later analyzed for Cl (chloride) concentrations. The Cl breakthrough-curves (relative Cl concentration vs. relative pore volume) were developed and the degree of preferential flow analyzed. Shape and other breakthrough-curve parameters, such as immobile pore-water fraction and initial breakthrough, indicated the occurrence of preferential flow through all columns. The degree of preferential flow, however, was greater in no-till than in conventional tillage columns (average immobile pore-water fraction was 56% for no-till and 49% for conventional tillage columns).