Effects of extraction technique on concentrations of soluble salts in soil saturation extracts

Abstract

Solution yield and saturation extract salinity for a range of south-east Queensland soils are described in relation to solution extraction by leaching, over a range of extraction times, and by centrifuging. Yield, pH, [Ca] and [HCO3] were affected by extraction technique. In leached extracts, compared with centrifuged extracts, solution pH was more variable and [HCO3] and [Ca] were higher. Leaching overnight consistently produced solution yields in excess of 20 g 100g-1 added water to saturation. Variations in these attributes reflect differences between the two extraction techniques which can be explained in terms of variable levels of CO2 in the solution collection assembly with air entry during extraction. Centrifuging minimised air entry and, hence, the gadliquid ratio in the extractor. The CO2 mediated changes are thus less for centrifuged than leached extracts. Centrifuging, as an extraction technique, therefore, has more relevance than leaching if specific mineralogic controls on solution composition are being determined.