Application of137Cesium to estimate erosion rates for understanding soil carbon loss on long-term experiments at Pendleton, Oregon

Soil erosion rates are a key factor for understanding changes in soil organic carbon. 137Cesium was used to estimate erosion rates in long-term cropping experiments in eastern Oregon. Based on the 137Cs measurements, RUSLE or EPIC estimates, and visual observations there is little evidence of water erosion at these experimental sites. Since there is little evidence of soil movement from the experimental sites to explain a steady decline in soil organic carbon (Rasmussen and Albrecht, 1998), then our study supports the conclusion that the major contributing factor for the declining soil organic matter is biological oxidation. The fallow conditions would provide excellent conditions for biological activity by microorganisms. Our study would indicate that under certain conditions biological oxidation is the most important factor for soil organic carbon loss. While there is great potential to sequester carbon in agricultural soils (Lal, et al., 1998), knowing the mechanism of carbon loss from the soil is necessary to determine its fate in the environment. While eroded soil carbon may end up being sequestered in the sediments of lakes and estuaries, biologically oxidized soil carbon will be released directly to the atmosphere as CO2.