COMPARISON AMONG AND EVALUATION OF CERAMIC POROUS CUP SOIL WATER SAMPLERS FOR NUTRIENT TRANSPORT STUDIES

Abstract

The use of commercially available porous cup soil water samplers for soil solution extraction was evaluated. Ortho-P, (NO₃ + NO₂)-N and potassium (K) were adsorbed by the porous cup during extraction of soil water samples, but the retention of (NO₃ + NO₂)-N was minimal. The screening of NO₃⁻ by the cup was not obvious. The retention of ortho-P and K was a function of solution concentration and the time of contact between soil solution and the cup. A rest period between extractions, during which samplers remained in contact with solution at zero tension, appeared to enhance phosphorus sorption capacity of the ceramic cup. Furthermore, phosphorus sorption was reversible in nature. The porous cup subjected to high solution concentration initially, released phosphorus when flushed with soilsolution of low concentration. It is recommended that several consecutive soil water extractions be carried out at high (0.6 bar) tension, using high flow rate porous cups. The sample collected in the last extraction should be used to determine true soil water quality.