@article{KuehnBrenningWehrhanetal.2009,
  author    = {K{\"u}hn, J{\"u}rgen and Brenning, Alexander and Wehrhan, Marc and Koszinski, Sylvia and Sommer, Michael},
  title     = {Interpretation of electrical conductivity patterns by soil properties and geological maps for precision agriculture},
  issn      = {1385-2256},
  doi       = {10.1007/s11119-008-9103-z},
  year      = {2009},
  abstract  = {Precision farming needs management rules to apply spatially differentiated treatments in agricultural fields. Digital soil mapping (DSM) tools, for example apparent soil electrical conductivity, corrected to 25A degrees C (EC25), and digital elevation models, try to explain the spatial variation in soil type, soil properties (e.g. clay content), site and crop that are determined by landscape characteristics such as terrain, geology and geomorphology. We examined the use of EC25 maps to delineate management zones, and identified the main factors affecting the spatial pattern of EC25 at the regional scale in a study area in eastern Germany. Data of different types were compared: EC25 maps for 11 fields, soil properties measured in the laboratory, terrain attributes, geological maps and the description of 75 soil profiles. We identified the factors that influence EC25 in the presence of spatial autocorrelation and field-specific random effects with spatial linear mixed-effects models. The variation in EC25 could be explained to a large degree (R (2) of up to 61\%). Primarily, soil organic matter and CaCO3, and secondarily clay and the presence of gleyic horizons were significantly related to EC25. Terrain attributes, however, had no significant effect on EC25. The geological map unit showed a significant relationship to EC25, and it was possible to determine the most important soil properties affecting EC25 by interpreting the geological maps. Including information on geology in precision agriculture could improve understanding of EC25 maps. The EC25 maps of fields should not be assumed to represent a map of clay content to form a basis for deriving management zones because other factors appeared to have a more important effect on EC25.},
  language  = {en}
}
@article{SauerSteinGlatzeletal.2015,
  author    = {Sauer, Daniela and Stein, Christine and Glatzel, Stephan and K{\"u}hn, J{\"u}rgen and Zarei, Mehdi and Stahr, Karl},
  title     = {Duricrusts in soils of the Alentejo (southern Portugal)-types, distribution, genesis and time of their formation},
  series = {Journal of soils and sediments : protection, risk assessment and remediation},
  volume    = {15},
  journal   = {Journal of soils and sediments : protection, risk assessment and remediation},
  number    = {6},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1439-0108},
  doi       = {10.1007/s11368-015-1066-x},
  pages     = {1437 -- 1453},
  year      = {2015},
  abstract  = {This paper reports on extremely thick and massive duricrusts in soils of two basins in the Alentejo (southern Portugal). Since different types of duricrusts (calcretes, silcretes and palycretes) have been reported from other regions in the Mediterranean, the purpose of this study was to identify the cementing agents in the duricrusts and to compare their composition in the two basins. Moreover, the study aimed at identifying the processes involved in duricrust formation, and especially the role of topography and lateral water and element transport in the landscape, and drawing conclusions about environmental conditions and time of duricrust formation. After studying an extensive number of road cuts in the field and mapping soil patterns in parts of the two basins by manual augering, ten pedons were selected for detailed description and sampling. Thin sections were analysed under a petrographic microscope, focusing on the micromorphology and optical properties of the cementing materials. Selected samples were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy to reconfirm the optical identification. The laboratory analyses included pH, carbonate contents, and X-ray diffraction analysis. The duricrusts in the eastern Sado basin are indurated by silica. Combination of XRD and thin section analysis allowed to identify opal-CT as a major component, while opal-A is present to a lesser extent, and chalcedony is very rare. The cementing materials of the duricrusts in the Oriola basin are palygorskite and calcite, which may occur alone or in combination within a soil profile. The thick duricrusts formed in the basins through precipitation of calcite, palygorskite and silica from lateral water flows, which ran from the Serra de Portel into the basins, during short moist seasons in a generally warm, semi-arid climate with strong evapotranspiration. Lithology of the upper catchment areas (element sources) and topography control the spatial distribution of the different duricrusts. Their formation took place mainly during the Pliocene. Palygorskite transformation to smectite in the upper parts of the palycretes indicates that palygorskite is unstable in the present (more humid, typical Mediterranean) climate. This study demonstrates the potential role of lateral water and element transport in landscapes that need to be considered in pedological studies and concepts, and the use of mineral indicators of past climates such as palygorskite and the ageing stage of silica precipitations as tools for reconstructing environmental conditions and possible time of duricrust formation.},
  language  = {en}
}