High resolution modelling of root zone processes using the R-SWMS model

The R-SWMS model that couples water flow in the root system with three-dimensional water flow and solute transport in the soil was developed recently (Javaux et al. 2008). This coupling requires that water flow and solute transport in the root zone are spatially resolved at the scale of single roots. It offers the possibility to describe processes in the soil-plant continuum in a more mechanistic manner avoiding empirical descriptions of root water uptake as a function of bulk matric potential, osmotic potential, root length density, and transpiration rate. Simulations of root water uptake by this model were used to derive macroscopic water uptake functions which are fully consistent with a mechanistic description of water flow in the soil-root continuum (Couvreur et al., 2012). By coupling flow and transport processes, the effect of root water and solute uptake on transport and its spatial variability in the root zone could be quantified (Schröder et al., 2012). Simulated solute transport towards roots and solute accumulation at root surfaces was used to calculate osmotic potentials at soil-root interfaces and their impact on water flow in the soil root system. These simulations are used to develop relations between osmotic and matric potential and root water uptake. By considering transport within the root system, transfer of plant hormones, which are produced in the root zone as a function of local soil water potentials, towards the shoot and their effect on transpiration regulation was simulated. This offers the possibility to simulate the impact of partial root zone drying and alternated root zone irrigation on plant transpiration. The high resolution simulations are used to interpret information about root zone processes that becomes available from tomographic imaging methods such as MRI and neutron tomography. From a comparison of simulation results with non-invasive measurements of root zone processes, parameters of the root system can be derived. Couvreur, V., J. Vanderborght, and M. Javaux (2012), A simple three-dimensional macroscopic root water uptake model based on the hydraulic architecture approach, Hydrol. Earth Syst. Sci., 16(8), 2957-2971 doi: 10.5194/hess-16-2957-2012. Javaux, M., T. Schröder, J. Vanderborght, and H. Vereecken (2008), Use of a three-dimensional detailed modeling approach for predicting root water uptake, Vadose Zone Journal, 7(3), 1079-1088 doi: 10.2136/vzj2007.0115. Schröder, N., M. Javaux, J. Vanderborght, B. Steffen, and H. Vereecken (2012), Effect of Root Water and Solute Uptake on Apparent Soil Dispersivity: A Simulation Study, Vadose Zone Journal, 11(3), - doi: 10.2136/vzj2012.0009.