Centennial scale temporal responses of soil magnetic susceptibility and spatial variation to human cultivation on hillslopes in Northeast China

Abstract

Soil loss is a significant environmental issue that causes soil degradation and threatens national food security in the black soil region of Northeast China. The magnetic susceptibility (MS) technique is a promising method for evaluating soil loss and estimating soil redistribution. In this study, undisturbed soil samples were selected from four typical black soil cropland slopes with 110a, 60a, 30a, and 20a cultivated durations at 10 cm intervals from the surface to a depth of 50 cm to measure soil MS. Based on measurable magnetic indexes, a quantitative relationship between MS and cultivation duration was constructed. The results indicated that: (1) The MS showed an approximate trend, namely 110a < 60a < 20a < 30a < 0a, the longer the sloping land was cultivated, the smaller the MS. (2) The reduction rate of χlf on the surface and underlying soil ranged from 1.57 to 3.27 and was also enhanced in the topsoil. (3) The relative difference value of MS among cultivation durations were greater at the lower slope than at the upper and middle slopes for all selected slopes; however, all positions became nearly constant after 50a of cultivation; (4) MS values substantially correlated in power function with cultivation duration on the entire slope and on three slope positions with r2 values from 0.50 to 0.86 and root mean square error values from 0.21 to 0.41. Soil MS in croplands varied with cultivation duration and was directly proportional to the increase in cultivation duration, which was used to establish soil redistribution and erosion patterns. The results of this study demonstrate that MS is a credible index for quantifying soil loss during continuous tillage at the centennial scale.