Identifying soil redistribution patterns by magnetic susceptibility on the black soil farmland in Northeast China

Erosion processes in the black soil region of Northeast China result in significant regional soil redistribution and crop production heterogeneity along slopes. It is difficult to link soil erosion and redistribution on a long-term scale using classical field plot monitoring or the costly 137Cs technique; however, magnetic susceptibility measurements can provide an economical tool to quantify soil redistribution over a large area and over a long duration. This study attempts to determine the variations of soil magnetic susceptibility on sloped farmland using soil sampling and to establish the relationship between patterns of soil redistribution and variations of magnetic susceptibility at different locations on a slope. Soil cores were collected along two typical transects on a cultivated slope and a reforested slope, respectively. The cores were 100 cm deep and were spaced at an interval of 10 cm; the samples were measured for mass-specific low-frequency magnetic susceptibility (χlf) and frequency-dependent magnetic susceptibility (χfd). The results showed that the χlf profiles at different slope positions on uncultivated reforested land were relatively homogeneous, revealing a similar pedogenic process across the entire slope. However, the χlf profiles at different slope positions on cultivated land were significantly different, exhibiting signs of a soil erosion and deposition process. Maximum soil loss (15.8%) occurred at the shoulder segment, and maximum soil deposition (25.1%) was observed at the footslope. However, at least 10.6% of the topsoil had been eroded and lost due to cultivation over the past 60 years in the study area. The results imply that magnetic susceptibility can be used to determine soil redistribution.