Soil crusts and deposits as sheet erosion indicators in southern Mali

Rills are indicators of erosion, easily recognized by farmers and extension workers. However, they are rare on fields in Mali with slopes of 0–3%, even though run‐off and sheet erosion may be a problem. The suitability of three other soil surface features as erosion indicators was therefore investigated: (1) structural crusts formed by rainfall impact without lateral soil movement; (2) in situ depositional crusts, formed by sedimentation leaving the finest particles on top; and (3) run‐off deposits of fine and coarse sand, formed after the removal of finer particles. Feature (1) occurred on the elevated parts and ridges, whereas (2) and (3) occurred in lower parts and in furrows. Soil cover with a run‐off deposit of coarse sand proved to be a suitable indicator and this was well explained by erosion risk: a 2% increase in slope related to a 9% increase in deposit cover. The extent of this deposit also related well to cotton yield from the previous season: a 30% increase in deposit cover was reflected in a 23% decrease in cotton yield. Only a few farmers confirmed that the deposits were produced by erosion. It is recommended that soil and water conservation programmes pay more attention to the presence of crusts and deposits.