Erosion rates evaluated by the 137Cs technique and direct measurements on long-term runoff plots under tropical conditions

Measured 137Cs losses (Bq m−2) from long-term runoff plots under tropical conditions and correspondent estimated soil erosion rates (Mg ha−1 year−1) were significantly correlated to directly measured soil losses of the same plots, during the same period (1963–2002). A tendency of higher 137Cs activities was observed in soil profiles of the bottom third part of runoff slopes that could be explained by the restricting effect of the collector system on the runoff flow or by tillage translocation. Despite of the very low 137Cs activity found in the soil of the plots, the isotopic technique yielded confident results, comparable to those obtained by the traditional direct measurements.