Wind Erosion in Western Queensland Australia

Chapter 4 –Modelling Soil Erodibility DynamicsQ )b= a.(%clay(4.2)where a and b are regression coefficients representing the intercept and rate of change in Qwith respect to percentage clay.While Leys et al. (1996) presented two erodibility curves relating to two surface treatments(Figure 2.4), Chepil (1953) presented a single regression equation fitted to data collected onsoils that had experienced a range of antecedent climate and management conditions. Theelevated erodibility of soils with clay content >27% assessed by Chepil resulted fromcrust/aggregate breakdown – the same process separating the two sets of data presented byLeys et al. (1996). The data presented by Leys et al. (1996) demonstrates that a powerfunction (e.g. Equation 4.2) will best model the condition of ‘minimum erodibility’ in soilsthat have maximum aggregation or crusting. In situations where soil moisture content is lowenough not to affect u *t , the equation for crusted soils can be taken to define the lower limit ofthe soil erodibility continuum.Eldridge and Leys (2003) reported on biological crust cover-aggregation relationships inrangeland environments. Their results demonstrate that decreasing crust cover results inlower dry aggregation levels by a linear relationship of the form:( )% DA = 18.03 + 0.79 %CC(4.3)where %DA is the percentage mass of dry aggregates >0.85 mm, and %CC is the percentagebiological crust cover (r 2 = 0.72, p < 0.001). The relationship was found to vary for differentsoil textures. While clay and loam soils were found to require low levels of crust cover tomaintain high %DA, sandy soils rely heavily on crust cover to provide adequate soilaggregation to minimize erodibility. Severe disturbance of crusts on loamy and clay soils istherefore required to instigate a significant increase in erodibility.Comparing the Leys et al. (1996) regression models for the cultivated and non-cultivatedsoils reveals the effects of disturbance on soil aggregation, crusting and erodibility. Withaggregate breakdown (increasing %DA < 0.85 mm) a vertical displacement of the curvedefined by Equation (4.2) takes place. For example, the curve will move from a low position105