Wind erosion in agricultural soils is dependent, in part, on the aerodynamic roughness length (z₀) produced by tillage ridges. Although previous studies have related z₀ to ridge characteristics (ridge height (RH) and spacing (RS)), these relationships have not been tested for tillage ridges observed in the North African agricultural fields. In these regions, due to climate and soil conditions, small plowing tools are largely used. Most of these tools produce non-aggregated and closely-spaced small ridges. Thus, experiments were conducted in a 7-m long wind tunnel to measure z₀ for 11 ridge types covering the range of geometric characteristics frequently observed in south Tunisia. Experimental results suggest that RH²/RS is the first order parameter controlling z₀. A strong relationship between z₀ and RH²/RS is proposed for a wide range of ridge characteristics.