Can measured soil hydraulic properties simulate field water dynamics and crop production?

Agricultural system models simulate soil water dynamics and crop evapotranspiration (ETc) and growth to enhance soil and crop management. To achieve this, simulations must be critically evaluated against field experimental data in different field management conditions. In many evaluations, simulations deviated from field measurements, which can be due to the quality of model input parameters. Replacing soil hydraulic properties indirectly derived from soil textural data by measured soil hydraulic property may decrease the discrepancy between measured and simulated soil water status. What is the benefit of using measured soil hydraulic properties in a model instead of pedo-transfer-function (PTF) based approaches to estimate the hydraulic properties indirectly? The objective of this study was to investigate the effect of using measured soil hydraulic property input parameters (SHPIP) as Root Zone Water Quality Model (RZWQM2) inputs compared to PTF-based indirectly derived hydraulic parameter inputs with and without calibration. A field experiment with soybean, corn, and fallow soil was conducted. Five model scenarios using measured SHPIP and SHPIP derived from soil texture as model inputs were created. The results indicate that, RZWQM2 showed a high sensitivity to the SHPIP calibration for fallow and corn season. Uncalibrated measured SHPIP yielded better simulation results than other SHPIP scenarios with regard to soil water flux, crop evapotranspiration, and soybean yield during the validation. While, the calibration of the SHPIP in corn and fallow slightly helped soybean soil water prediction at the surface depth. Hence, with representative measurements of SHPIP, it was possible to improve model simulations even without calibrating the input parameters.