Chloride concentration distribution under oak hedgerow: an indicator of the water-uptake zone of tree roots?
Résumé
In agroforestry systems, root activity of trees may either reduce nutrient leaching beneath neighboring crops or compete with them. A previous study reveals high chloride (Cl) accumulation in the soil under a bottomland oak hedgerow in western France. Our study tests whether Cl can be used as an indicator of the spatial extent of tree root activity. Cl was analyzed in soil profiles up to 2 m deep along transects perpendicular to hedgerows. One site was explored in detail to examine the role of hedgerow position on the slope, supplemented with multi-annual and multi-site studies on bottomland hedgerows. Upslope Cl accumulation was highest near the tree line (and up to 6 m away) and around 1 m deep. Downslope it extended up to 18 m from the tree line and near the surface. This difference was caused by differences in water availability or physical soil constraints. Cl accumulation was found in both temporal (multi-annual) and spatial (multi-site) studies. Cl accumulation under oak hedgerows can be used to identify the lateral extent and depth of water uptake by roots. It results from root activity over many years. The method is more suitable for poorly drained soils.