Effects of secondary soil aggregates on threshold friction velocity and wind erosion

Secondary aggregates (clods) attenuate wind erosion and land degradation by increasing surface roughness and reducing wind friction velocities at the soil surface. However, aggregates with low stability are erodible and may increase dust emissions by particle abrasion under saltation bombardment relative to non-erodible aggregates. It is still not clear exactly how different secondary aggregate properties reduce, and in the presence of saltators potentially increase, wind erosion and dust emission. The objective of this study was to quantify the effects of erodible soil aggregates on the threshold friction velocities (u(*t)), aerodynamic roughness length (z(o)), and soil loss of loessial soils in the inland Pacific Northwest (iPNW) of the United States. The impact of erodible secondary aggregates in attenuating wind erosion was evaluated in terms of secondary aggregate lateral cover and density. Secondary aggregates were tested in a wind tunnel using five levels of aggregate densities. Secondary aggregates appeared to restrain wind erosion as z(0) and u(*t) increased with increasing aggregate cover, but may significantly change wind erosion patterns by releasing more fine dust particles by abrasion. We found that, while abrasion losses contributed up to 69.3% of total soil loss for a sandy loam, total soil loss still decreased for all soils. Aggregates with greater stability may reduce soil loss with increasing secondary aggregate densities, and the rate of reduction in soil loss was up to two times higher than that for soil aggregates with lower stability.