EVALUATION OF POROUS CUP SOIL-WATER SAMPLERS UNDER CONTROLLED FIELD CONDITIONS - COMPARISON OF CERAMIC AND PTFE CUPS

The value of soil water samples used in ecological studies is highly dependent on the quality of the samplers. Tension soil-water samplers are widely used to extract soil solutions, and the samplers are often tested in the laboratory under conditions that differ significantly from field conditions. This study describes a field procedure useful for comparison of two different tension soil-water samplers. Ceramic and PTFE cups are compared. There were no differences in the concentrations sampled by the two different types of sampler for Na+, K+, Ca2+, Al3+, NH4+, H+ and NPOC (non-purgeable organic carbon). Change in the applied vacuum in the range 0 to -0.4 x 10(5) Pa did not change the concentrations of chemical species in the collected soil water. The ceramic cups collected significantly larger amounts of water due to differences in the hydrostatic characteristics of the two samplers. It was found that the ceramic samplers collected the highest concentrations of Mg2+ in some situations. The results are evaluated and discussed in relation to the possible sources of errors and the temporal and spatial variabilities.