FLOWS: a model to simulate water and solutes fluxes in agricultural and environmental systems. 1. Theory and applications with intercode benchmarking

FLOWS (FLOws of Water and Solutes in soils) is a dynamic physically-based model to simulate water flow and solute transport in the soil–plant–atmosphere system. The numerical code was written in MATLAB. One-dimensional vertical transient water flow is simulated by numerically solving the 1D form of the Richards equation (RE) using an implicit, backward, finite differences scheme with explicit linearization. As for the solutes, the code solves the 1D Advection Dispersion equation (ADE) by an explicit, central difference scheme, allowing for a relatively easy inclusion of non-linear adsorption and other non-linear processes. The model produces information on the time evolution of (among many other outputs): soil water contents and pressure potentials in the soil profile; solute (tracers, adsorbed, volatile and reactive solutes) concentrations in the soil profile; water and solute uptake and actual evapotranspiration for simulated crops; deep percolation water and solute fluxes; root uptake of water and solutes, also in presence of water and osmotic stresses; water fluxes and related solute fluxes to runoff; drainage water fluxes and related solute fluxes; irrigation fluxes computed by the model; and temperature in the soil profile. Compared to other existing models, some specificities of FLOWS model are: (1) integrated simulation of carbon, nitrogen and phosphorus transformations and transport contextually to the simulation of water contents and fluxes; (2) macroscopic root uptake; (3) irrigation management, by allowing to optimize the time scheduling and volumes according to some criterion based on the average pressure head in the root zone; (4) the possibility of running multi-site simulations, which may be especially important for spatially distributed simulations; and (5) an interactive graphical user interface, allowing the user to easily handle even large input files and seeing the simulation results by graphical display of the main output variables.