The fractionation of soil aggregates associated with primary particles influencing wind erosion rates in arid to semiarid environments

Soil particle size distribution (PSD) plays an important role in wind erosion studies and sediment transport modeling. Few studies have been done focusing on the susceptibility of different soil fractions to wind erosion under natural conditions. This study was performed to measure in-situ wind erosion rates using a portable wind tunnel facility on 60 undisturbed soils of arid to semiarid regions. The effects of primary (i.e. clay, silt, and sand particles) and 16 secondary (aggregate) size classes were attributed to wind erosion rates. Moreover, the boundaries between major fractions of the soils (i.e. micro-aggregates, meso-aggregates and macro-aggregates) were determined. The result showed that clay and silt particles and also surface rock fragment were inversely proportional to wind erosion rates as power functions, whereas sand content showed a positive exponential relationship. The size ranges of < 53 mu m, 53-300 mu m and > 300 mu m were distinguished for the micro-aggregates, meso-aggregates, and macro-aggregates, respectively. The meso-aggregate fraction was proportional and the micro-aggregate and macro-aggregate fractions were inversely proportional to wind erosion rates. Furthermore, a narrower size range of 75-150 mu m was detected as the most erodible soil fraction. The distribution of the primary particles in the major aggregate fractions was different, so that in the meso-aggregates, sand particles and in the micro-aggregates and macro-aggregates, silt and especially clay particles predominated. It is concluded that the presence of macro-aggregates (> 300 mu m) associated with fine primary particles (clay) can significantly reduce wind erosion rate rather than the sandy soils containing weaker aggregates.