Horizontal and vertical variations in soil fertility in response to soil translocation due to tillage-induced erosion on sloping cropland

Research on how tillage-induced soil redistribution impacts horizontal and vertical variations in soil fertility remains limited in non-mechanized agriculture regions. Twenty-time successive tillage were performed over a 3day period by manual hoeing on a steep slope within the purple soil area of Southwest China. Profile variations of Cs-137 activities and soil physiochemical properties were evaluated across various slope locations of pre-, 5- and 20-operation tillage. The integrated fertility index (IFI) was calculated using fourteen soil properties and two approaches: i) the total data set (TDS) and ii) the minimum data set (MDS). From hilltop to bottom of the slope, soil erosion rates determined from Cs-137 data ranged from 16.4 to 1.70 t ha(-1) yr(-1) before tillage, 20.90 to -7.17 t ha(-1) yr(-1) after 5 tillage events and 28.10 to -12.13 t ha(-1) yr(-1) after 20 tillage events. The IFI showed variations between 0.48 and 0.55 (0.59 and 0.67), 0.38 and 0.59 (0.43 and 0.72), and 0.33 and 0.61 (0.32 and 0.77) before tillage, after 5 and 20 tillage events, respectively, based on the TDS (MDS) approach. The IFI values tended to increase along the slope transect from the top to toe portions and decreasing gradually with soil depth both before and after tillage. The variation in IFI can be ascribed to the spatial redistribution of soils, with 52.17 % attributed to downhill soil movement, 43.96 % to vertical mixing due to tillage, and 3.87 % to the interaction between these processes. Our findings revealed that long-term tillage operations have a twofold impact on soil fertility: they result in soil movement downhill from various upslope areas and the vertical mixing of soil material from different layers, both of which influence soil fertility on sloping cropland.