Erodibility of Vertisols in relation to agricultural practices along a toposequence in the Logone floodplain

Knowledge of the combining effect of agricultural practices and slope on soil erodibility is important to promote their suitable use and constitutes a key parameter for their sustainable conservation. The aim of this study was to characterize vertisols from the Logone floodplain and evaluate their erodibility in relation to the agricultural practices and slope in order to suggest the well managing strategies to be diffused. Vertisols were characterized by describing their profile type and their erodibility was assessed by sampling topsoils at 3 positions along a toposequence (upslope, midslope and footslope). Erodibility indexes were computed by exploiting physicochemical data. The studied vertisols were classified as gleyic Vertisols. They are clayey (19-42% of clay), slightly basic (pH~7.3) and display high organic matter (OM) content and cation exchange capacity. Smectites and kaolinite were the main clay minerals associated with quartz. The water dispersible clay, clay dispersion ratio and dispersion ratio diminished from the upslope to the footslope, while clay aggregation showed an opposite trend. Hence, vertisols from the upslope and midslope cropped were more erodible than those from the not cropped footslope. From the statistical analysis, it appeared that Na+, Ca++ and K+ contributed to vertisols erodibility while Mg++, OM and amorphous Fe promoted aggregate stability. Managing these vertisols will tend to limit N and K rich inputs (urea and NPK fertilizers); control liming strategies and encourage substantial OM inputs. No-tillage or minimum tillage oriented perpendicularly to the slope are the practices to be implemented.