Lateral differentiation of Albeluvisols under the impact of subsurface drainage

Albeluvisols are temporarily waterlogged due to the argillic horizon that limits downward movement of rainfall water. These soils are hence frequently drained for cropping. Drainage modifies water movement in both direction and velocity, inducing a gradient in waterlogging conditions perpendicularly to the drain. Over time, it may induce a lateral differentiation of the soil solid phase with the distance from the drain. This study aims at characterising and quantifying this differentiation. Albeluvisols are characterised by the following horizon succession: A, Eg&BT, BTgd. The two last horizons exhibit a complex juxtaposition of white-grey, ochre and pale-brown volumes, and numerous black concretions or impregnations. In order to study the impact of drainage on the evolution of such soils, we have to characterise the soil differentiation perpendicularly to the drain by quantifying changes in the quality and the abundance of the different pedological volumes

Impact of drainage on soil-forming mechanisms in a French Albeluvisol: Input of mineralogical data in mass-balance modelling

International audienceResearch on soil pedogenesis has mainly focused on the long-term soil formation and has most often neglected recent soil evolutions in response to human practices. Such recent soil evolutions are however of considerable interest to study the timing of soil forming processes in response to changes in environmental conditions. In this paper, we model the Albeluvisol evolution in response to agricultural drainage. This was considered as a model case to study the velocity of mineralogical changes in soil as a result of eluviation and redox processes. We used a space-for-time substitution approach in combination with mass balance modelling based on mineralogical data in order to identify and characterise the mineralogical transformations responsible for the recent soil evolution in response to subsurface drainage. This approach allowed demonstrating that the main effects of subsurface drainage are (i) increasing precipitation of Mn oxides and Mn-rich ferrihydrite with decreasing distance to the drain as a result of the change in redox conditions and (ii) increasing loss of clay-sized oxides and smectites due to the enhanced eluviation in the vicinity of the drain. Both processes induce significant matter fluxes in comparison with those that occurred over the long-term soil formation. Nowadays, the precipitation of Mn oxides and Mn-rich ferrihydrite seems to still be active in the studied soil. On the opposite, the eluviation process appears less active than immediately after the drainage network installation, if not totally inactive. It thus demonstrates that some soil processes may have significant impact on the soil mineralogical composition even if they are only active over very short periods of time after a change in environmental conditions