Evidence for the formation of Luvisols/Alfisols as a response to coupled pedogenic and anthropogenic influences in a clay soil in Finland

Abstract

Clayey soils with a cryic soil temperature regime and an aquic soil moisture regime are extensive in southern Finland but they have rarely been pedogenically described. A pedon in a field that has been in agricultural use since the 17th century was characterized and features indicative of human-influenced pedogenic processes were identified. Owing to intensified agriculture, the soil has become drier than ever before. Natural shrink-swell and anthropogenic turbation processes had destroyed the rock structure to a depth of 72 cm. Groundwater monitoring during nine years proved that in several years the soil had a chance to desiccate down to 150 cm, resulting in wedge-shaped prisms and desiccation joint planes. The cracks and root channels serve as routes for clay translocation. Illuvial clay, observed in thin sections, had the maxima (>1%) in the Btg (38–72 cm) and BCtg2 (112–140 cm) horizons, corresponding to the effective drainage depths during ditch drainage until 70 years ago and subsequent subsurface tile drainage, respectively. Seventy years of improved drainage seems to be sufficient to give rise to an argic/argillic horizon. This feature is likely manmade but, being irreversible, it must be taken into account in soil classification. In this climate, agriculture seems to influence pedogenesis strongly throughout the solum far below the plough layer. Luvisols (WRB) or Cryaqualfs (Soil Taxonomy) have not been documented in a clay soil in Finland or Sweden before.;