Assessing soil erosion in a semiarid ecosystem in Central Argentina using ¹³⁷Cs and ⁷Be measurements

Argentina is a Latin American country which encounters soil degradation problems. The most productive regions have implemented conservative land practices (no-till). However, agricultural frontier has been displaced to marginal lands with arid and semiarid climates, with the consequent disappearance in many areas of native forest and land degradation. In this work, the fallout of gamma-emitting radionuclides, ¹³⁷Cs and ⁷Be, was jointly used to assess changes in soil erosion in a recently converted semiarid ecosystem into agricultural land. ¹³⁷Cs was utilized to estimate the erosion over the past 60 years, whereas ⁷Be was employed to estimate the erosion after the conversion of the area to cultivated land and soil tillage. For ¹³⁷Cs the Proportional Model (PM), the Mass Balance Model II (MBMII) and the MODERN model were used, for ⁷Be the Profile Distribution Model (PDM) and the MODERN model were used. ¹³⁷Cs indicates mean erosional rates of 8.2, 10.5 and 6.5 Mg ha^-1 a^-1, using MBMII, PM and MODERN, respectively, and that a soil layer between 0.5 and 0.8 mm was annually lost by erosion. By applying a ⁷Be tracer, we measured erosion rates of 2.4 and 3.3 Mg ha^-1 (with PDM and Modern, respectively), indicating the loss of the upper 0.2 mm of soil. This erosion can be attributed to a few heavy rainfalls that occurred within the past 90 days. The results suggest that current land management practices have led to an increase in soil erosion. This could be attributed to the fact that the soil remains bare after crop harvest, which may compromise its conservation and future productivity.