Changes in organic carbon concentration and organic matter compound of erosion-delivered soil aggregates

Soil organic carbon (SOC) is a key property for both fertility and carbon level control in the atmosphere. SOC changes in soils are ruled by tillage and erosion. Initial SOC erosion was investigated using a laboratory rainfall simulator. Six precipitation events were modelled on cultivated, bare Cambisol monolith with various slope steepness and surface roughness under a constant intensity of 80 mm h⁻¹. The total amount of soil loss was divided into four aggregate size classes (<0.05, 0.05–0.25, 0.25–1.00, >1.00 mm). Altogether, 72 sediment and 16 in situ samples were analysed. The results show a loss of SOC concentration that increased at all aggregate sizes, the highest (~200 %) found in the smallest grain size, while conversely nitrogen concentration decreased in the 250–1000 μm class. Consequently, soil organic matter (SOM) compounds underwent changes during the initial erosion processes in soil losses of all aggregate sizes. The detached SOM was less polymerised and had more aromatic character compared to that of the in situ soil in all aggregate size classes. The type of SOM enrichment found through the soil loss in this study is a result of two parallel processes within initial erosion phenomenon: (I) chemical degradation of the most labile SOM components and (II) mineralogical changes in the smallest aggregate class (<0.05 mm) that results in a considerable amount of quartz leaving the aggregates and remaining on the surface. The results suggest that tillage operations regarding stability of the smallest aggregates have particular importance in SOC conservation.