The role of soil surface properties on the particle size and carbon selectivity of interrill erosion in agricultural landscapes

- The role of surface properties on the selectivity of interrill erosion was examined.
- The surface properties governing soil loss and the process of selectivity differed.
- Texture, slope, moisture, cover and organic matter influenced particle size selectivity.
- Texture, slope and organic matter influenced organic carbon selectivity.
- The enrichment of fine-grained and organic-rich particles changes over time.

The selective nature of interrill erosion - the preferential mobilization and transport of soil particles - can lead to the enrichment of fine-grained soil particles (< 63 μm) and organic carbon (OC) within the mobilized soil. This study investigated the effects of slope gradient, vegetative cover, soil moisture content, texture and organic matter content, as well as their interactions on soil loss, particle size distribution and organic carbon content of soil mobilized under simulated rainfall within two contrasting agricultural regions in Canada. Overall, it was found that the eroded material was enriched in both fine-grained and carbon-rich particles relative to the source soil. It was demonstrated that dispersing and sieving both the source soil and the mobilized soil to < 63 μm (i.e., removal of sand and large particulate organic matter) reduced the relative enrichment of both fine-grained soil particles and OC, which would allow for a more direct comparison of physical and biogeochemical properties between the source and mobilized soil. Furthermore, it was demonstrated that while the soil loss and the degree of enrichment were negatively correlated, there were differences in which soil surface properties had a significant effect in determining soil loss and the selectivity of both fine-grained and organic-rich soil particles and how these surface properties interacted. This suggests that while soil loss may be a good predictor of the degree of enrichment, the factors that control these two processes are different, which is important in understanding the process of selectivity. It was also shown that the OC content of both the source and mobilized soil was positively correlated to the degree of soil aggregation in addition to the silt and clay content.