Bimodal Arya&Paris Pedotransfer Function - bimAP

Soil hydraulic properties (SHP) are essential for modeling water movement in agro-environmental systems, but direct measurements are costly and time-consuming. Pedotransfer functions (PTFs) offer an alternative by estimating SHP from easily measurable soil properties. Most PTFs are empirical, relying on soil texture without considering soil structure, which significantly affects hydraulic conductivity. Recently, a new physically based PTF, bimAP, was developed. It extends the unimodal Arya-Paris PTF (unimAP) into a bimodal model by incorporating aggregate-size distributions, improving its ability to capture SHP variability. Saturated hydraulic conductivity (K0) is estimated by using the Kozeny-Carman model with parameters derived from the upper portion of the soil water retention curve (SWRC). To facilitate bimAP’s application, a dynamic Excel spreadsheet was developed. By inputting soil physical parameters and the scaling parameter (αAP), users can calculate macropore and matrix porosity ratios and predict the bimodal SWRC. The spreadsheet also enables αAP calibration by minimizing differences between measured and estimated soil water contents using the Excel solver. The solver can further optimize Brooks-Corey water retention parameters for K0 calculation and refine the full bimAP SWRC using Durner parameters fitting. If measured SHP data is unavailable, αAP can be estimated via multiple linear regression using soil properties such as particle-size distribution, aggregate-size distribution, bulk density, and macropore ratio. This dataset includes the Excel Spreadsheet that can do the calculations of bimAP as well as the classical unimAP.