Overwinter changes in wind erodibility of clay loam soils in southern Alberta

Soil dry aggregate size distribution (DASD) and surface roughness are important factors affecting wind erodibility. This study monitored overwinter changes in DASD and surface roughness and identified relationships with climatic variables in the chinook-dominated region of southern Alberta. A different site was monitored in each of three winters (18 Sept. 1992 to 12 May 1993; 26 Oct. 1993 to 29 Apr. 1994; 30 Aug. 1994 to 24 May 1995) on Dark Brown Chernozemic clay loams (fine-loamy, mixed, Typic Haploborolls). The DASD was expressed as geometric mean diameter (GMD) and wind erodible fraction (EF). The GMD ranged from 1.88 to 0.08 mm in 1992-1993, from 9.05 to 1.17 mm in 1993-1994, and from 4.71 to 0.80 mm in 1994-1995. The EF ranged from 38.9 to 74.0% in 1992-1993, from 12.6 to 43.7% in 1993-1994, and 31.3 to 55.0% in 1994-1995. Surface roughness was measured parallel (C(par)) to tillage direction on two of the sites. Using the chain method, C(par) ranged from 15.1 to 3.7% in 1993-1994 and from 14.4 to 3.3% in 1994-1995. Regression analysis with time revealed significant exponential decay for GMD (R2 = 0.57 in 1992-1993, 0.97 in 1993-1994, and 0.78 in 1994-1995) and C(par) (R2 = 0.98 in 1993-1994, 0.91 in 1994-1995) and a positive linear fit for EF (R2 = 0.57 in 1992-1993, 0.91 in 1993-1994, and 0.62 in 1994-1995). Three overwinter periods, differentiated by the timing and form of precipitation and designated as "fall rain/show", "winter snow", and "spring snow/rain", were used to assess the changes in EF using cumulative freeze-thaw cycles, precipitation, and snow cover variables. Results indicated that precipitation, which directly influences soil water content, is necessary for freeze-thaw cycles to be effective in disrupting soil aggregates. Snowmelt and spring rainfall appear capable of reducing wind erodibility on these clay loam soils by promoting soil crusting. Our study showed that overwinter soil properties affecting wind erodibility are highly transitory and that the timing and form of precipitation played a major role in determining wind erosion risk in southern Alberta.