DRAINAGE WATER SAMPLING IN A WET, DUAL-PORE SOIL SYSTEM

Two experiments were conducted on an undisturbed Hublersburg silt loam (Typic Hapludult) soil to evaluate two different soil solution sampling techniques. The two techniques were employed simultaneously to sample the leachate at depths of 38 to 120 cm when water was added at the soil surface with known concentrations of NO3-N (0-579 ppm) and Cd2+ (0.0001-5.45 ppm). After each controlled water addition to the surface, soil water samples were taken for analysis with porous cup soil water samplers and with devices located in a sub-surface horizontal tunnel. Large differences in ion concentration occurred between data obtained from the soil water samplers and from the horizontal tunnel. Calculations based on water retention data indicated that in excess of 90% of the total flow occurred in pores drained by water potentials of 0 to -20 cm of water. This pore class is considered to be dominated by interped cracks and to cause a channeling of solution past the porous cup samplers. It was concluded that under wet soil conditions, soil water samplers are not suitable for monitoring the chemical quality of the water percolating through the soil profile.