The relationship between landform and the distribution of soil C, N and P under conventional and minimum tillage

The objective of this study was to examine the interactive effects of tillage and land forms (erodibility) on the redistribution of C, N and P within an agricultural landscape. Soils were sampled from an undulating maize field in central Belgium. Half of the field was under conventional tillage (CT), while the rest was under minimum tillage (MT) management. Based on slope and curvature characteristics, depositional and erodible zones were identified in both tillage treatments. We analyzed 400 surface (0–5 cm) soil samples, and 25 soil profiles (0–100 cm). Concentrations of native C, maize-derived C, total N, Olsen P, and moisture content in the 0–5 cm soil layer showed distinct spatial patterns with variogram ranges from 30 to 90 m. These patterns were related to local differences in texture and landform. In general, nutrient concentrations were greater in lower, depositional areas, and smaller in higher, erodible areas. In addition, the impact of landform was more pronounced in CT than MT. Three years after the implementation of the tillage treatments, native C, total N and Olsen P stocks (0–46 cm) in erodible zones were about 40% less under CT than under MT. However, in depositional zones, nutrient stocks were equal between the tillage treatments. Differences in erosion rates, the distribution of Olsen P and maize-derived C indicated that this pattern was mainly caused by soil transport induced by erosion since the implementation of the tillage treatments, rather than local differences in decomposition rates. We concluded that the influence of landforms on the stabilization and redistribution processes of nutrients is greater within CT than MT. Therefore, interactions between landform and agricultural management need to be considered in regional soil organic matter inventory assessments.