Relationship of the presence of a non-calcareous clay-loam horizon to DEM attributes in a gently sloping area

The initial objective of this study was to identify relationships between t errain attributes and soil cover over a Loessic flat area covering a limest one plateau. The second objective was to determine those energy factors (fl ow path, solar radiation, wind intensity) which could improve the understan ding of morphology and soil genesis. We describe 341 field observations tak en over 1600 ha of an experimental area used for monitoring the water and n itrate supply in the Petite Beauce Region (100 km to the Southwest of Paris ). For each observation, several soil variables were encoded. One was the p resence of a non-calcareous day-loam (NCCL) horizon. Relief is very smooth in this region (mean slope around 0.5%). The main terrain attributes were d erived from a Digital Elevation Model (DEM) at 20 x 20 m and assigned to th e pedological observations. A multiple logistic regression was used to anal yse the relationship between the NCCL horizon and terrain attributes. Speci al statistics were used for aspect, because of the circular nature of this variable. The results show a strong relationship between the presence of NC CL horizon and slope gradient and slope aspect, while hydrological paramete rs are not correlated with this horizon. The mean angle of the aspect frequ ency of the NCCL horizon was calculated and compared to the mean angles of wind direction and solar radiation balance. There is a small difference bet ween wind direction and aspect frequency of the NCCL horizon. This result c onfirms the role of wind in the spatial pattern of soils. Further data are required to better understand the combination of several factors (role of v egetation) and the age of the reshaping. (C) 1999 Elsevier Science B.V. All rights reserved.