Soil erosion potential of organic versus conventional farming evaluated by USLE modelling of cropping statistics for agricultural districts in Bavaria

Organic agriculture (OA) aims to identify a production regime that causes less environmental problems than conventional agriculture (CA). We examined whether the two systems differ in their susceptibility to soil erosion by water. To account for the large heterogeneity within the rotations practised on different farms, we chose a statistical evaluation which modelled erosion using the USLE method from the cropping statistics for 2056 districts in Bavaria (70 547 km2; 29.8% arable). Physical conditions of erosion were determined in a rectangular grid yielding 13 125 grid-cells of c. 5 km2 each. For validation, erosion was measured in 10 sub-watersheds on two neighbouring OA and CA farms over 8 years (287 erosive events). On average, about 15% less erosion on arable land was predicted for OA than for CA due to the larger area of leys, although OA occupies areas that are susceptible to erosion more often than CA. The same conclusions could be drawn from the validation data. These data also demonstrated that erosion could be reduced considerably below 1 t ha±1 yr±1 with best management practices under both farming systems. In contrast, at the countrywide scale, cropping did not change adequately with site conditions favouring erosion. The need for erosion control seems not to in¯uence crop rotation decisions on erosion-prone sites.