Tuesday, 11 July 2006 - 2:05 PM

Coupled Pedogenic and Anthropogenic Influences on a Clayey Luvisol/Alfisol in Southwestern Finland.

Markku J. Yli-Halla1, Delbert Mokma2, Larry P. Wilding3, and L. R. Drees3. (1) Department of Applied Chemistry and Microbiology, University of Helsinki, Building D, P.O. Box 27, Helsinki, 00014, Finland, (2) Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824, (3) Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843

Clayey soils are extensive and important for agriculture and development in southern Finland. These soils have a cryic soil temperature regime and an aquic soil moisture regime. Their pedogenesis is likely to be slow in the native state but human activities, particularly agricultural drainage, may have had a significant effect on their pedogenesis. These impacts were studied in a clayey soil (40% in Ap and 60-80% in underlying horizons) in Jokioinen in southwestern Finland using macromorphology, micromorphology, and physical and chemical analyses. Desiccation of the sediments began as the isostatic rebound after the Weichselian glaciation brought the area above water (about 8,000 YBP) and was increased with native forests and agronomic cereal crops upon artificial drainage. The area has been in agricultural use since the 17th century. Artificial drainage was first conducted with shallow ditches. Tile drains were installed about 70 years ago at a depth of 1 to 1.2 m. Anthropogenic ditch drainage coupled with manure inputs increased plant growth and transpiration. Later, tile drainage, improved crop varieties and use of chemical fertilizers further enhanced soil desiccation. Rock structure has been mostly destroyed by natural shrink-swell and anthropogenic turbation in Ap, Bt and Btg horizons (0-72cm). Rock structure was observed in increasing amounts in the BCtg horizons to the Cg horizon in which it occupies more than 50% of the volume. Subangular blocky structure dominated Ap and Bt horizons, while the major structure in Btg and BCtg horizons was prismatic parting to angular blocky. Many prisms were wedge-shaped in the lower BCtg horizon reflecting that desiccation joint planes likely formed subsequent to anthropogenic drainage. This is further supported by platy desiccation cracks observed in the Cg horizon (140-150 cm). As a result of increased aeration, reduced Fe and Mn began to oxidize forming nodules and pipestem concretions in a gray matrix. Nodules in Ap, Bt, and Btg horizons had stress clay coatings around them indicating they are not active. But in lower horizons the diffuse boundaries around these Fe-Mn features indicate they are currently active. Illuvial clay was observed in thin sections of each horizon below the Ap, with a maximum in the BCtg2 horizon (112-140 cm), which has strong (0.5 mm) continuous bands of translocated clay particularly along prism faces and previous root channels. It is unlikely that this magnitude of clay illuviated into this horizon when it was saturated, i.e. before tile-drainage. The clay that eluviated from upper horizons likely originated from increased pedality caused by tillage and desiccation cracks. The abundance of clay permitted clay eluviation to begin shortly after the dried clayey materials were rewetted and suspended in percolating waters. This process was favored by high shrink-swell potentials (COLE values ranging from 0.03 to 0.07), and abundance of vermiculite and biotite clays. The major pedogenic processes currently active in this soil are: 1) shrink-swell pedoturbation, especially in Ap and B horizons, and formation of prismatic structure in lower horizons; 2) formation of Fe-Mn nodules and pipestem concretions by zonation of free-iron oxizes; 3) clay translocation; and 4) weathering of minerals, such as biotite. Rate of disappearance of rock structure in this moist clayey soil appears to be slower than the rate of translocation of clay. Micromorphically, the pedon has more than 1 percent illuvial clay in subsoil horizons that still have substantial amounts of rock structure. Such clay illuviation suggests that 70 years of improved agricultural drainage and farming systems practices is sufficient time to form an argic/argillic horizon. Accordingly in the WRB system and Soil Taxonomy, respectively, this soil was classified as a Gleyic or Haplic Luvisol and a Typic Cryaqualf, previously not recognized in Finland. Even if the anthropogenic drainage were ceased, the illuviated clay forming the argic/argillic horizon in this soil would be an irreversible feature.

Back to 1.2B Soil System Behavior in Time - Oral
Back to WCSS

Back to The 18th World Congress of Soil Science (July 9-15, 2006)