Evaluation of the influence of sample preparation and extraction technique on soil solution composition

Soil solutions were extracted by immiscible liquid displacement with trichlorotrifluoroethane and by centrifuge drainage from surface and subsoil samples having a wide range of chemical and physical properties. Extractions were performed on field-moist samples and on air-dry samples which were re-wetted to different matric suctions and for different lengths of time. The composition of the soil solution obtained was the same with both methods of extraction when samples had been pre-wet to a matric suction of 0.1 bar. Immiscible liquid displacement extracted solution from a krasnozem surface soil at suctions as great as 15 bar; in contrast, centrifuge drainage failed to extract solution from this soil at > 3 bar. The concentration of ions in solutions extracted by displacement from soils with increasing matric suction rose to a far greater extent than that anticipated if concentration was the only mechanism operating. In re-wet air-dry samples, major cations and anions were at equilibrium levels in solution after incubation for 1 day; longer incubation times resulted in an artificial elevation of ionic strength through mineralization of organic matter in some surface samples. The levels achieved after 1 day were similar to those present in solutions extracted from field-moist samples