Soil Organic Carbon Redistribution by Erosion on Arable Fields

Colloids are thought to move easily, consequently both mineral and organic colloids are overrepresented in runoff and soil loss, which causes selective erosion. Soil loss compound is a function of scale. The enrichment of soil organic carbon (SOC) and of the clay fraction in soil loss was studied at two sites in Hungary. A rainfall simulator was applied to describe selective erosion at micro (< 1 m(2)) and plot (2 x 6 m) scale. At field scale, soil loss samples were taken from 25 to 50 m intensively tilled runoff plots to assess SOC losses. At plot scale, selective erosion takes place as redistribution within the plot with crust formation. Thin sections demonstrate the horizontal structure of the particles on the surface covered by SOC and clay colloids. The rate of SOC enrichment is inversely proportional to the amount of soil loss. Enrichment is significant in the settled (coarse) part of soil loss, while - in contrast to the plot scale results - there is no SOC surplus in the suspended part. SOC components of high molecular weight seem to be increasingly vulnerable to erosion and they are overrepresented in soil loss. Because of their high stability carbon sequestration occurs in the buried horizons.