For sustainable crop production in semi-arid environments with low and erratic rainfall (<800 mm), runoff must be minimized and water conserved. However, little is known about how soils in semi-arid southern Africa respond to cultivation. This study investigated the hydrological and physical responses of a fersiallitic soil to conventional (flat) and improved (tied ridge) tillage practices over four seasons under natural and simulated rainfall conditions in Zimbabwe. Changes in soil surface roughness and the development of crusts were investigated and related to variation in the runoff ratio (total volume of runoff/total volume of rain). Relationships between runoff, rainfall intensity and antecedent precipitation index (API is an indicator of soil moisture content based on daily rainfall) were established for both systems. For the tied ridge system, API showed no significant contribution to runoff prediction. This reflects the greater and more stable depression storage capacity of the furrow in the tied ridge system. By comparison, the depression storage capacity of the flat system is temporary in nature and, as the micro relief of the soil surface weathers and crusts develop, its capacity declines, as does the time to ponding and runoff generation.
