USE OF THE RADIOACTIVE ISOTOPE CESIUM-137 TO EVALUATE THE EROSION RATE ON A DEGRADED SLOPE IN MEXICO

In the Ejido La Gavia, in the municipality of Almoloya de Juarez, State of Mexico, the soils dedicated to maize cultivation and cattle grazing show high levels of erosion. Therefore, it is convenient to estimate the soil erosion rate of crops in the sub-basin with the use of tracers. The hypothesis of this study was that the annual erosion rate (Mg ha(-1) y(-1)) on the degraded slope of the Ejido La Gavia can exceed the maximum permitted limits of erosion for this type of agricultural soils. The objective of this study was to quantify the annual erosion rate in a maize plot and a degraded slope of the Ejido, and to identify the deposit areas of the radioactive isotope Cesium-137 (Cs-137). The soil sampling of the degraded slope was made in four transects with ten samples in each one, obtaining a total of 40 soil samples. Five reference sites were included, out of which the Cs-137 profile was measured at 50 cm depth. At the reference site, the maximum value found was 6.8 Bq kg(-1) at a depth of 10 cm, with 96 % of the Cs-137 content observed in the first 20 cm of the soil profile. The inventory of Cs-137 on the study slope was between 10.2 and 535.1 Bq m(-2), which was lower than that found in the selected reference site of 584.3 Bq m(-2). The mass balance model 2 was used, obtaining a soil loss rate with values of -23.5, - 27.5, - 20.9, and - 22.0 Mg ha(-1) y(-1). Soil erosion rates in the study four site transects far exceeded the permissible limit of 6.7 Mg ha(-1) y(-1).