Methods and Materials
Soil loss influenced by clay amendment was assessed for four soil series commonly found across the inland Pacific Northwest (iPNW) of the northwestern United States (Figure 1). The soil of the iPNW developed from eolian deposition of loess eroded from Rocky Mountain outwash deposits, as well as the loess and volcanic deposits (Chandler et al., 2004; Zobeck et al., 2011). The four soils were obtained from four locations in Washington State. Two silt loam soils (Athena silt loam, Walla Walla silt loam) were collected from a humid continental climate area which receives an average annual precipitation > 499 mm. The two sandy loam (Warden sandy loam, and Farrell sandy loam) were collected from a semi-arid area which receives an average annual precipitation < 341 mm. Soil texture is the primary soil property affecting wind erodibility (Zobeck, 1991a). Both sandy loams have larger sand content resulting in higher erodibility than the silt loam soils, nonetheless the latter is characterized by greater PM10 emission potential (Table 1). All sites were in a winter wheat (Triticum aestivum )-summer fallow rotation (WW-SF) except the Colfax, WA site which was in a winter wheat-safflower-summer fallow rotation. Lands in fallow are typically at greater risk for wind erosion due to limited vegetative cover, little surface roughness, and poor aggregation. More details of the soils used in this study are given in the Table 1.
Samples of the four soil types were collected from the upper profile (30 mm) at the field sites during the fallow phase of a WW-SF or WW-SW-SF rotation or after sowing in late spring. Warden sandy loam and both silt loams were previously used to assess wind erodibility characteristics in the region (Sharratt and Vaddella, 2012; 2014), Sharratt et al. (2013), and Pi and Sharratt (2019).