Clay Movement in Sand Columns and its Pedological Ramifications

Abstract

Movement of clay particles and other colloids through soil profi les has been investigated extensively during the past few decades. The pathway of movement is generally accepted as being predominantly downward. This study investigated the hypothesis that clay and colloids can move upward by capillarity, and is concomitant with water movement. To test this hypothesis, two experiments were conducted. The fi rst experiment used an empty transparent plastic column standing in a 500-mL glass beaker and packed with dry sand. A reddish clay suspension was used with a concentration of 24.2 g L−1, a pH of 7.1, and an electrical conductivity (EC) of 0.05 S m−1. The clay suspension was added to the beaker so that it could move upward within the sand column by capillarity. The second transparent plastic column was placed empty in a 500-mL glass beaker and was packed with a 30-cm layer of dry sand overlain by a 5-cm layer of sandy loam, which was then overlain by a 20-cm layer of dry sand. A water table was established to test the likelihood of clay particles moving upward via capillarity. In each experiment, the movements of the clay-sized materials were visually tracked using a digital camera. The results of the fi rst experiment showed that clay particles moved 25 cm upward and even accumulated at the surface. Clay particles moved upward in the second experiment and formed some clay bands in the sand layer overlying the sandy loam layer. Peer Reviewed Papers