Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility Controlsflux was determined for nine soils in cultivated and non-cultivated (crusted and aggregated)states (Section 2.2.3). They found an exponential relationship between percentage dryaggregates (%DA) and erosion rate:Iw0.078%DA= 8.33exp(2.11)where Iw is the erosion rate at 65 kmh -1 (tha -1 min -1 ), and %DA is the dry aggregation >0.85mm (%). The relationship holds for a range of soil textures, suggesting %DA is morephysically related to erosion rates than percentage clay content, which requires one regressionequation to define the erodibility of various surface conditions (Leys, et al., 1996). Thisphysical relationship stems from the direct effect of aggregate (grain) size on u *t (Equation2.5). The expression confirmed the results of a similar study by Chepil (1953).Fryrear et al. (1994) developed a regression model for computing the erodible fraction (EF)of soils based on soil texture and chemical data.EF= 29.09+ 0.31( Sand)+ 0.17( Silt)+ 0.33( SC) 4.66( OC) 0.95( CaCo3)(2.12)where Sand is the soil sand content, Silt is the soil silt content, SC is the ratio of sand to claycontents, OC is the organic carbon content, and CaCO 3 is the calcium carbonate content. Animportant characteristic of the model is that it was derived from time-averaged data, and doesnot account for temporal variations in aggregation and the erodible fraction driven by climatevariability and land management.Few published studies have examined temporal variations in soil aggregation in response toclimate variations, land use or land management practices. The majority of existing studieshave examined the effects of freeze-thaw cycles on soil aggregation in cultivated lands inNorth America (e.g. Chepil, 1954; Bisal and Ferguson, 1968; Merrill, 1999; Bullock et al.,2001). Despite the global significance of wind erosion in the world’s hot, dryland regions,research that addresses temporal changes in soil erodibility in these environments is scarce.While the effects of soil surface conditions on erodibility have been described in someresearch, for example Gillette et al. (1980) and Gillette et al. (1982), a significant gap remainsin our understanding of temporal changes in soil aggregation in rangeland environments.43