Concept for Pointing Out Vulnerable Sandy Areas in Relation to the Leaching of Pesticides to the Groundwater.

A concept for pointing out vulnerable sandy areas in relation to the leaching of pesticides to the groundwater has been developed in Denmark. The concept focuses on the inherent volumetric content of clay and silt and the amount of organic matter in the upper meter of the soil. Based on a developed raster-based soil property map of Denmark with a resolution of 250 to 500 m it is possible to implement the concept. This work aims at testing the validity of the soil map in a selected area and to come up with recommendations for how the soil map can be used by local authorities. The soil property map was tested in selected areas in three different landscape types (Saale moraine, glaciofluvial, and aeolian deposits). Soil samples were excavated from nine points at two depths (A and B horizon). At each point, samples were taken in a 20 by 20 m grid sampling design giving a total of 16 soil samples in each depth. In the laboratory, the samples were analyzed with the respect to bulk density and the content of sand, silt, and organic matter. The results from the comparison between predicted values (from the soil map) and measured values showed a good relation between the total content of clay and silt. However, the amount of organic matter was overestimated by the soil map. Vulnerable areas in the study area were pointed out using the data from the soil map. Here the results showed that most vulnerable areas were found in areas with glaciofluvial and aeolian deposits. Aggregated areas were pointed out having different levels of vulnerability. We conclude that it is possible to use the Danish soil map to point out areas with the risk a pesticide leaching in combination with other maps related to the agricultural practice.