Solute Transport Modeling in Overland Flow Applied to Fertigation

A model of solute transport in overland flow is developed and applied to the simulation of surface fertigation. Water flow is simulated using the depth-averaged, one-dimensional shallow water equations. Solute flow is represented by an advectiondiffusion model. The resulting set of three partial differential equations is sequentially solved at each time step. First, water flow is computed using the explicit two-step McCormack method. Based on the obtained velocity field, solute transport is explicitly determined from the advection-diffusion equation using the operator split technique. Four field experiments involving fertigation events on an impervious free-draining border were performed to validate the proposed model and to obtain estimates of Kx, the longitudinal dispersion coefficient. A value of Kx = 0.075 ms satisfactorily reproduces the field experiments. The model is also applied to the simulation of a fertigation event on a pervious border. A sensitivity analysis is performed to assess the dependence of fertilizer distribution uniformity on the value of Kx. Finally, the proposed model is compared to a previous model based on pure advection. INTRODUCTION Fertigation is an interesting alternative for the fertilization of surface irrigated crops. The limitations to the use of surface fertigation stem from the alleged low uniformity and efficiency of surface irrigation systems. Hanson et al. (1995) reported that the performance of typical surface irrigation systems in California cannot be statistically distinguished from that of pressurized irrigation systems. Clemmens and Dedrick (1994) arrived at a similar conclusion when discussing the potential application efficiency of different irrigation systems. Recent developments in the design and