Clay transformations following a leaching experiment on an acid brown soil

Detailed studies on soil processes commonly involve the use of reconstructed soil columns (e.g. James & Riha, 1989; Liu et al., 1990; Smith et al., 1995). This approach reduces the inherent variability associated with field experiments, allows the simultaneous monitoring of solution and solid phases, and limits the interactive effects from concomitant processes. Sample pretreatment (airdrying, sieving, mixing, aeration) (Runge, 1974) together with leaching conditions and laboratory procedures may, however, result in a varying degree of disturbance, which in turn could cast doubt on the extrapolation of results to field conditions. Until now, most reports of disturbance associated with leaching column experiments have focused on soil solution composition, such as increased nitrate leaching (Boutin & Robitaille, 1989; David et al., 1991). Little attention has been given to the chemical evolution of the solid soil phase, particularly the <2 lam fraction. In this paper, the general soil properties (<2 mm fraction) as well as the mineralogy of the clay fraction (<2 I.tm) were determined for the A1 and B horizons of an acid brown forest soil, before and after a leaching experiment with reconstructed soil profiles. An attempt was made to relate the modifications of the soil solid phase to the chemical evolution of the leachates. M A T E R I A L S A N D M E T H O D S Soils and sampling site The Oi, Oe, A1 and B horizons were collected from an acid brown soil with a mull humus (typic Dystrochrept; USDA, 1992), located in the French Ardennes (Croix Scaille massif). The parent material of the soil consisted of weathered Revinien shales, covered by a silty loam layer. The vegetation was a coppice with Oak (Quercus petraea Liebl.) standard.