Simulating soil loss on farmland hillslope cultivated in centennial periods using magnetic susceptibility in Northeast China

Soil erosion is a major worldwide threat to agriculture, food security, and ecosystems. Northeast Black Soil Region is an important food base in China and has an important strategic position for ensuring food security. Black Soil Region suffered severe water erosion due to long-term unreasonable utilization. The loss of topsoil in farmland decreases the amount of indispensable fertile soil for plants and reduces land productivity. The magnetic susceptibility (MS) technique has been successfully applied in describing farmland soil redistribution pattern as a reliable, economical, and rapid method, but it still need further study in soil loss quantification. In this study, four typical black soil farmland slopes (cultivated in 110a, 60a, 30a, and 20a) and a reference forest slope were selected, while undisturbed soil samples were collected at a 5 cm interval from the surface to 50 cm depth. The objective is to (1) utilize soil MS values (including χ_lf and χ_fd%) and other soil property indexes to represent soil loss on farmland slope; (2) recommend Δχ (the ratio of the difference between MS of the slopes cultivated in two certain periods) as an indicative index of soil loss rate to convert current soil erosion pattern in spatial scale to the certain historical period soil loss in temporal scale; (3) verify the feasibility of MS value in estimating farmland soil loss in multi-temporal scale by cultivation period. The results indicated that: (1) The MS approximately followed the trend of “110 a < 60 a < 20 a <30 a < Forest” at plow layer, that is, the slopes in longer cultivation periods expressed greater MS differences than reference slope; (2) Δχ values were greater at lowerslopes than those at upperslopes and middleslopes, and Δχ at all positions became nearly stable after 50a cultivation; (3) Δχ values were remarkably correlated exponentially with cultivation periods not only on the whole slope but three separated slope positions, with r² from 0.50 to 0.86. Soil MS reflects soil redistribution and erosion patterns on farmland hillslope. MS values on farmland vary with cultivation periods which denotes soil redistribution. The MS variation caused by tillage was greater at lowerslope than middleslope and upperslope. Soil loss has exponent relation to the cultivation periods. Farmland in longer cultivation periods was associated with greater soil loss, but soil erosion and deposition tend to be stable for slopes in longer cultivation periods. This study demonstrates the feasibility to quantify soil loss in continuous tillage within centennial periods using the MS technique.