Estimate of soil erosion on cultivated soils using 137Cs measurements and calibration models:: A case study from Nakhla watershed, Morocco

Despite the seriousness of the erosion problem in the Nakhla watershed. there are still only limited data on the rates of soil loss on cultivated land on steep slopes. Thus. there is a need for more information for optimizing strategies for soil conservation. Recent concern over problems of soil degradation and the off-site impacts of accelerated erosion has highlighted the need for improved methods of estimating rates and patterns of soil erosion by water. In this paper, soil erosion and deposition rates have been studied using the Cs-137 technique in upstream part in the Nakhla watershed on cultivated soils (Larbaa Beni Hassan area). which is known to suffer soil erosion. Multiple transect sampling was established parallel to the slope, and Cs-137 inventories were determined for the sampling points. After establishing the local reference inventory (3073 Bq m(-2) inventories on all the transects with three calibration models: propor-soil erosion and deposition rates were estimated using the Cs-137 model (PNI). mass balance model I (MBN4 1) and mass balance model 2 (1\413%12). The magnitude of the soil erosion rates depends on many factors, including the location of sampling. the local topography. and the soil properties. Estimated soil erosion rates for the using MBN4 1: and from 0.4 to 56.4 t ha(-1) yr(-1) using study area varied from 0.4 to 28.9 t ha-1 yr(-1) using PM: from 0.5 to 66.9 t ha(-1),yr(-1). MBM2. The deposition ranged, respectively. from 0.3 to 8.0 t ha(-1) yr(-1) for PM from 0.4 to 14.5 t ha(-1) yr(-1) for MBM1. and front 0.3 to 11.5 t ha(-1) yr(-1) for MBM2. The sediment delivery ratio is about 98%. For one Selected plot, L11. the erosion rates show a clear relationship with the range of slopes in its three different horizontal paris. Estimates of soil redistribution rates were interpolated by means of kriging using Surfer 7.0 software. Two representative transects were Selected to identify the contribution of tillage on Cs-137 redistribution by using mass balance model 3. It is observed that the pattern of Cs-137 redistribution is dominated by water erosion and that the contribution of tillage redistribution remain is smaller.