Estimates of Long and Short Term Soil Erosion Rates on Farmland in Semi-Arid West Morocco Using Caesium-137, Excess Lead-210 and Beryllium-7 Measurements

The aim of the present work was to investigate both long and short term soil erosion and deposition rates on agricultural land in Morocco and to assess the effectiveness of soil conservation techniques by the combined use of environmental radionuclides (137Cs, excess 210Pb and 7Be) as tracers The study area is an experimental station located in Marchouch 68 km from Rabat (western part of Morocco). Experimental plots have been installed in the study field to test the no-till practice under cereals as a soil conservation technique, and comparing it to the conventional tillage system. Fallout 137Cs and 210Pbex allowed a retrospective assessment of long term (50 and 100 yrs respectively) soil redistribution rates while fallout 7Be with a short half-life (53 days) was used to document short term soil erosion associated with short rainfall events for different tillage systems and land uses. From 137Cs and 210Pbex measurements the rates of soil redistribution induced by water erosion were quantified by using the Mass Balance 2 model. The net soil erosion rates obtained were 14.3 t ha-1 a-1 and 12.1 ha-1 a-1 for 137Cs and 210Pbex respectively resulting in a high sediment delivery ratio of about 92%. Data on soil redistribution generated by the use of both radionuclides are similar, indicating that the soil erosion rate did not change significantly during the last 100 years. In addition, the soil redistribution rates due to tillage were estimated using the Mass Balance 3 model. The global results obtained from 7Be measurements during the period 2004-2007 suggest that the soil loss is reduced by up to 30% when no-till management is practised when compared to the conventional tillage or uncultivated soil. (author)