QUANTIFYING WIND EROSION ON SUMMER FALLOW IN SOUTHERN ALBERTA

Wind erosion on summer fallow is a pervasive problem on the semi-arid Canadian prairies. Quantifying soil losses caused by wind erosion in t erms of weight of topsoil per unit area has not been possible in the p ast. A Wind Erosion Prediction System (WEPS), being developed by the A gricultural Research Service, U.S. Department of Agriculture, will cal culate average soil loss/deposition over a specified area and time. A WEPS validation site was established on a fallow field in southern Alb erta in November 1990. Using BSNE dust samplers, a total of 16 erosion events (wind storms causing measurable soil movement) were monitored between April 1991 and May 1992. Total soil loss was 144 Mg/ha (64.5 t on/ac). Losses due to individual storms varied from 0.3 to 30.4 Mg/ha (0.1 to 13.6 ton/ac). Based on the fastest rate of soil renewal report ed, it would take about 17 years to replace the topsoil removed. Storm minimum wind speed (threshold conditions for erosion) declined as the fallow season progressed, indicating increased susceptibility to eros ion. This was likely a result of the weathering action of precipitatio n during the summer and freeze/thaw activity during the winter. Precip itation and crusting acted as deterrents to erosion later in the fallo w season. The increased surface roughness caused by a seeding operatio n also protected against erosion.