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

Soil dry aggregate size distribution (DASD) and surface roughness are impor tant Factors affecting wind erodibility. This study monitored overwinter ch anges in DASD and surface roughness and identified relationships with clima tic variables in the chinook-dominated region of southern Alberta, A differ ent site was monitored in each of three winters (18 Sept. 1992 to 12 May 19 93; 26 Oct. 1993 to 29 Apr, 1994; 30 Aug. 1994 to 24 May 1995) on Dark Brow n Chernozemic clay loams (fine-loamy, mixed, Typic Haploborolls), The DASD was expressed as geometric mean diameter (CMD) and wind erodible fraction ( EF). The GMD ranged from 1.88 to 0.08 mm in 1992-1993, born 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,,) to tillage di rection on two of the sites, Using the chain method, C,, ranged from 15.1 t o 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 (R-2 = 0.57 in 19 92-1993, 0.97 in 1993-1994, and 0.78 in 1994-1995) and C-par (R-2 = 0.98 in 1993-1994, 0.91 in 1994-1995) and a positive linear fit for EF (R-2 = 0.57 in 1992-1993, 0.91 in 1993-1994 and 0.62 in 1994-1995). Three overwinter p eriods, differentiated by the timing and form of precipitation and designat ed as "fall rain/snow", "winter snow", and "spring snow/ rain", were used t o assess the changes in EF using cumulative freeze-thaw cycles, precipitati on, and snow cover variables. Results indicated that precipitation, which d irectly 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 pr omoting soil crusting. Our study showed that overwinter soil properties aff ecting wind erodibility are highly transitory and that the timing and form of precipitation played a major role in determining wind erosion risk in so uthern Alberta.