THE USE OF MAGNETIC-SUSCEPTIBILITY TO MEASURE LONG-TERM SOIL REDISTRIBUTION

Several studies have documented the severity of recent soil erosion on the Canadian prairies where cultivation started about a century ago. Little quantitative information is available on erosion before 1960. T his study attempts to quantify post-and pre-1960 soil erosion in a sma ll cultivated basin near Saskatoon, Saskatchewan, Canada, by measuring Cs-137 and magnetic susceptibility (chi) distribution with depth. Soi l cores were collected along six transects (three across closed depres sions and three across the drainage channel) in the cultivated field, and one transect across an uncultivated depression. The cores were sli ced into 3-cm layers and the soil analyzed for Cs-137, chi, and organi c and inorganic C. High variability in chi with depth in eroding areas (as indicated by Cs-137) made it impossible to use chi to quantify pa st soil losses in these locations. However, these eroding upper and mi ddle slope positions have a much higher chi than lower slope areas whe re soil deposition occurs and where the variability in chi with depth could be used to estimate soil deposition. Estimating soil deposition from the chi vs. depth profiles was more successful in the closed depr essions than in the drainage channel, where the chi profiles may refle ct the variable source areas of the materials rather than the pedologi cal conditions. The data indicated that soil deposition since 1960 has been about 30 to 50% of that prior to 1960. This suggests that soil d eposition rates, and by implication, soil erosion rates, have been rel atively steady since cultivation of these soils started, although ther e are clear indications that the spatial pattern of deposition has var ied. (C) 1998 Elsevier Science B.V.