A simple dynamic method to estimate anion retention in an unsaturated soil

The anions Br- and NO3- are commonly adsorbed non-specifically by the highl y weathered soils found in tropical regions. We used a simple dynamic techn ique to determine their retention, using the so-called "Perroux tube", and we compared these results with those obtained from leaching experiments. Th e method was tested on a ferrallitic soil from New Caledonia which is rich in aluminium and iron oxides. From the resident concentrations observed, we obtained retardation values of 1.1 and 1.15 for bromide and nitrate respec tively, using respective input concentrations of 0.025 and 0.1 M. A numeric al model using these results predicted the flux concentrations obtained fro m the leaching experiments quite well, thereby proving the utility of this simple technique. ((C) Academie des sciences/Elsevier, Paris.).