Contrasting Hydrological Regimes in Two Ploughed Forest Soils in Upland Wales

Contrasting hydrological regimes in a cambic stagnohumic gleyand an ironpan stagnopodzol were monitored at the Tywi Forest,Mid-Wales, during the hydrological year 1988–1989. Variationsin the hydrological behaviour of each soil were observed inrelation to hillslope topography and the localized influenceof plough furrows and planting ridges. High rooting densitiesin the well-structured O horizon of the stagnohumic gley encouragedlateral seepage above the relatively impermeable subsoil andconcentrated summer drying in the surface horizons. Marked subsoildrying appeared to be related to deeper root penetration whereunsaturated subsoil conditions prevailed in upslope areas orbeneath planting ridges. In contrast, the ironpan stagnopodzoldid not have impeded drainage due to structural features andthe roots penetrating the E horizon and ironpan. Moreover, thesubsoil was coarsely textured and freely draining. Consequently,rooting was more extensive and hydrological regimes were moreuniform and not simply related to topography. Soil disturbanceand extensive root penetration in plough furrows appears topromote preferential water movement during storm events andcreate drier summer soil conditions.