Plot‐Scale Solute Transport in a Semiarid Agricultural Soil

In semiarid areas, agricultural production is determined by limited water and nutrient supply. To develop efficient management practices, it is of importance to predict solute transport. In line with this, we present observed and calculated plot‐scale solute transport in an agricultural experimental field in northern Tunisia. A pulse of Br − ‐tagged water was applied on the surface of two small field plots and leached under steady‐state soil water conditions. Solute samples were withdrawn through ceramic samplers at five different depths within each plot. The experimental data indicated a high degree of by pass or preferential flow within the small plots and nonsigmoid breakthrough curves, suggesting tailing phenomena and immobile fractions of soil water. The data were evaluated using the classical two‐parameter convection‐dispersion equation (CDE) and the four‐parameter non‐equilibrium convection‐dispersion equation (NECDE). Pore water velocities, v , and dispersion coefficients, D , were calculated by fitting the analytical solution of these two models to the breakthrough curves based on individual sample locations as well as using all samples in the plot simultaneously. None of the models could be fitted when data from all solute sampling depths were used in the optimization simultaneously. When using data at individual sample locations, the fit was somewhat better for the NECDE than for the CDE. The estimated values of D and v could be described by a power law relationship.