SWIM3: Model Use, Calibration, and Validation

SWIM3 is the latest release in the family of SWIM (Soil Water Infiltration and Movement) models that provides efficient solutions to the Richards and advection-dispersion equations for use in studies of soil water and solute dynamics. This version of the model has been designed specifically for use in farming systems simulation. Development within the APSIM (Agricultural Production Systems Simulator) framework enables SWIM3 to be combined with a wide range of soil and crop models to simulate a variety of agricultural systems. Other improvements in this release provide a new approach for specifying soil hydraulic properties from simple measures of soil water behavior. The simplicity of this new approach makes such a mechanistic numerical model more accessible to farming systems researchers. The effectiveness of this approach and the utility of SWIM3 for use in farming systems analysis is demonstrated using data from two long-term trials with different soils, climates, and cropping systems. These examples show how the design of SWIM3 allows model parameterization from consistent and well understood emergent soil properties in a simple but meaningful way. Access to the model and involvement in its ongoing development is welcomed via the APSIM Community Source Framework.