Perusmaata

Perusmaata is a Finnish term used in soil science to refer to the parent material, the underlying geological material from which soils develop. The word is the partitive form of perusmaa, meaning “some base soil” or “parent material.” In English, perusmaata is commonly translated as parent material or substrate. It covers bedrock as well as unconsolidated deposits that are weathered to form soil, such as glacial till, sands, gravels, loess, and volcanic ash.

Soil formation begins with weathering of the perusmaata, producing mineral particles and influencing soil pH, texture, and nutrient status. The nature of the perusmaa strongly affects drainage, water-holding capacity, and the mobility of certain elements. In Nordic soil surveys, perusmaa is a key reference layer for describing and interpreting soil profiles alongside horizons.

Regionally, different perusmaat yield characteristic soil types; for example, soils developed on crystalline bedrock may be acidic with low base saturation, while those on calcareous glaciofluvial deposits may be more neutral to alkaline and higher in calcium. The concept is also used in land-use planning, agriculture, forestry, and environmental assessment to anticipate how base material conditions influence vegetation, groundwater chemistry, and pollutant transport.

See also: soil science, pedology, parent material, bedrock, soil horizon.