TENSION INFILTROMETER CONTACT INTERFACE EVALUATION BY USE OF A POTASSIUM-IODIDE TRACER

Tension infiltrometer (disc permeameter) measurements may be adversely affected by small variations in experimental procedures. Published te nsion infiltrometer procedures are not adequate for all tension infilt rometer studies. A potassium iodide solution was infiltrated through t ension infiltrometers into packed soil columns in PVC tubing to evalua te the effect of permeameter contact variations at the silica sand/mem brane interface. Packed columns minimized the effects of macropores, s oil type variability and layering, allowing improved setup procedures to be developed. The spatial distribution of the potassium iodide solu tion on horizontal cross-sections of the column, at the surface, and v arious depths, was examined wing a starch and bleach technique which f orms a blue-black potassium iodide-starch-bleach complex. The dye stai ning technique allowed assessment of the causes of variability Tension infiltrometer setup procedures were developed which resulted in repro ducible tension infiltration curves and patterns as indicated by a pot assium iodide tracer (during the initial 10-min phase). Despite using improved permeameter setup procedures there was non-uniform wetting an d infiltration of packed columns of a sandy loam soil and a sandy clay loam soil at tensions of 0.6 kPa and 1.2 kPa, respectively. This was attributed to non-uniform wetting of the contact silica sand at the me mbrane interface. Assumptions that the flux through the silica sand co mpensates for imperfect membrane contact may not be justified The deve loped procedures will aid other researchers using tension infiltromete rs to decrease variability between replicates.