A system for obtaining soil solution extracts and soil water retention curves using a bench centrifuge with fixed angle rotors

Abstract

A centrifugation system is proposed for recovering soil solution extracts from disturbed natural soils. The water retention curve (WRC), which is related to the hydraulic properties of soil, was determined as a way to define the range of suctions applied for the purpose of soil water extraction. The design of the centrifugation device, the analysis of the experimental procedure and its validation are the aims of this work. Since centrifugation time is an important parameter for water extraction, a systematic study was performed. Although very long centrifugation times are generally required to guarantee equilibrium is reached, a time period of 60 min was used in the tests. The van Genuchten model was fitted to the experimental results of retained moisture versus effective suction, representing the matric potential and achieved thru the angular velocity of the rotor. The results obtained by this new approach were compared with the results obtained using the pressure chamber. This comparison revealed a systematic reduction in the amount of solution extracted at high suctions (above 100 kPa) regarding the pressure chamber. A feedback effect was confirmed by using ceramic sintered-perlite beads instead of sintered glass beads to support the soil specimen in the device adapted to the centrifuge. The proposed system was able to extract soil solutions in a fast, repeatable, and simple way.