Assessment of erosion rates from microphyte-dominated calcareous soils under rain-impacted flow

Intact soil monoliths with surfaces of varying microphytic crust cover were collected from a calcareous earth soil in a semi-arid belah–rosewood woodland near Wentworth in south-western New South Wales. Monoliths were tested for their susceptibility to erosion by rain-impacted flow using a laboratory rainfall simulator. The erosive stress applied to each surface was controlled by varying the flow depth between 4 and 8 mm whilst maintaining a flow velocity of 25 mm/s using 2·7 mm raindrops falling 11·2 m at average rainfall intensities of 65 mm/h. Increasing the cover of microphytic crusts on the surface resulted in a significant (P = 0·001) reduction in sediment concentration. A linear model incorporating percentage cover and distribution of cover accounted for 46% of the variance in soil erosion. A significant relationship was also found between the coarse fraction (>0·053 mm) and crust cover (P = 0·012) at the 4-mm depth. Management practices such as overgrazing, trampling, and fire, which reduce the cover of crusts in this landscape, will lead to increased erosion hazard.