Linking functional structural plant models with root water uptake models in earth system models

3D models of root growth, architecture and function are evolving as they become important tools that aid the design of agricultural management schemes and the selection of beneficial root traits. However, while benchmarking is common for water and solute transport models in soil, 3D root-soil interaction models have never been systematically analysed. Several interacting processes might induce disagreement between models: root growth, sink term definitions of root water and solute uptake and representation of the rhizosphere. The extent of discrepancies is currently unknown. Thus, a framework for quantitatively comparing such models is required. We propose, in a first step, to define benchmarking scenarios that test individual components of the complex models: root architecture, water flow in soil and roots, solute transport in soil and roots. While the latter will focus mainly on comparing numerical aspects, the root architectural models have to be compared at a conceptual level as they generally differ in process representation. Therefore defining common inputs that recreate reference root systems in all models will be a key challenge. In a second step, benchmarking scenarios for the coupled root-rhizosphere-soil models can be defined. We expect that the results of step 1 will enable us to better interpret differences found in step 2. We expect that this benchmarking will result in improved models, with which we can simulate various scenarios with greater confidence, avoiding that future work is based on accidental results caused by bugs, numerical errors or conceptual misunderstandings and will set a standard for future model development