Impact of recent conversion to organic farming on physical properties and their consequences on runoff, erosion and crusting in a silty soil

The aim of this study was to assess the influence of a recent conversion to organic farming on the physical properties, particularly the aggregate stability, of soils that are prone to soil crusting, as well as their impact on runoff, soil erosion and soil crusting dynamics. Experiments were conducted in the area of Brie, France, in two agricultural fields separated by 400 m with similar slopes and soil types. They consisted of physical measurements of the soils as well as simulated rainfalls with different intensities. No significant differences were detected among the bulk density, soil water retention or saturated hydraulic conductivity. The aggregate stability, measured both under simulated rainfall and in a laboratory, was significantly higher in the organic management field (OF) than in the conventional management field (CM), indicating that CM soils are more prone to soil crusting than OF soils. The influence of this difference was quantified using rainfall simulations in the field. Within the CM field, runoff occurred with a runoff coefficient (RC) of 4.8% and 6.9% when the rainfall intensities were 25 and 40 mm h−1, respectively, while in the OF field, no runoff was observed at these intensities. However, slight runoff was observed when the intensity was 50 mm h−1. Soil losses followed the same trend. Depositional soil crusts were observed in the plots wherein runoff transpired. These results evidence the benefits of recent conversion to organic farming in silty soil to the aggregate stability and consequently soil crust dynamics, runoff genesis and soil erosion.