Soil & Tillage Research 69 (2003) 127–137 Soil erosion evaluation in a small basin through the use of 137 Cs technique Alfonso Bujan a,∗ , Oscar J. Santanatoglia b , Celio Chagas b , Marcelo Massobrio b , Mario Castiglioni b , Marta Yañez a , Hugo Ciallella c , Jorge Fernandez c a CNEA, Av. del Libertador 8250, 1429 Buenos Aires, Argentina b Facultad de Agronom´ ıa, Universidad de Buenos Aires, Av. San Martin 4453, 1417 Buenos Aires, Argentina c Autoridad Regulatoria Nuclear, Av. del Libertador8250, 1429 Buenos Aires, Argentina Abstract Soil erosion significantly affects the most productive lands in Argentina, particularly the region called “Pampa Ondulada”. Quantification of the actual rates and patterns of soil loss is necessary for designing efficient degradation control strategies. The aim of this investigation was to gather using the 137 Cs technique a reliable set of data of erosion and sedimentation rates, in order to describe the long-term erosive landscape dynamic in a 300 ha basin representative for the “Pampa Ondulada” region of Argentina. The general topography of the basin is undulated with slopes gradients between 0 and 2.5% and slope lengths up to 800 m long. The main land use consisted in annual cropping under conventional tillage. For the soil erosion study in the basin the 137 Cs technique was used, which is based on the comparison between the 137 Cs inventories surveyed with a local reference 137 Cs profile. The sampling strategy was based on a multiple transect approach. The estimated mean soil erosion rates obtained applying Mass Balance Model 2 for the studied hillslopes ranged between -11.5 and -36 t ha -1 per year and fitted the low and moderate erosion classes according to FAO. These values ranged beyond the admitted tolerance. Sedimentation was observed at the lower landscape positions probably related to changes from convex to concave slopes. The application of the 137 Cs technique in the studied basin proved to be a useful and sensible tool for assessing erosion/deposition rates. In areas with low topographic gradients like the Pampa Ondulada region, the slope length appears to be an important property for predicting spatial patterns of erosion rates. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Basin; Soil erosion; Sedimentation; 137 Cs method; Pampean Region 1. Introduction It is widely recognized that accelerated soil erosion is a serious global problem. The agents of erosion are water and wind, but the main causes are improper land use and inadequate cultural practices. One third of the arable lands in the “Pampa Ondulada” region, ∗ Corresponding author. Tel.: +54-1-3798597; fax: +54-1-3798540. E-mail address: bujan@cae.cnea.gov.ar (A. Bujan). about 1 600 000 ha, are affected by erosion, in Ar- gentina (SAGyP, 1995). Quantification of the actual rates and patterns of soil loss/deposition is necessary for designing degradation control strategies. Classical methodologies for soil loss assessment have important limitations because they are expen- sive and time consuming. That is why not enough information is available for the fit of prediction models like universal soil loss equation (USLE) (Wischmeier and Smith, 1978) and WEPP (Lane and Nearing, 1989). Direct measuring field methods do 0167-1987/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0167-1987(02)00134-4