Background and aims <p>Root water uptake (RWU) depends on root development, influenced by water and salt stress (WAS). Modeling RWU requires calibration of soil and root parameters using lysimeter data, which is challenging. The study introduces a global sensitivity index-based estimability method for parameter assessment and selection, optimizing them using observations from lysimeter experiments.</p> Methods <p>A variance-based global sensitivity and estimability analyses was performed on the HYDRUS-1D model. The analyses evaluate the impact of soil hydraulic and stress parameters on pressure head, soil moisture, bottom flux, and electrical conductivity. Interactions among parameters across the root zone were analyzed for model parameter selection. The selected parameters were calibrated from soil-column lysimeter experiments on berseem (<i>Trifolium alexandrinum</i>) under saline and non-saline conditions.</p> Results <p>The analyses identify water stress and residual soil moisture as less estimable, while major soil and salt stress parameters as more estimable, especially from bottom flux and soil moisture data. Excluding saturated soil moisture, which strongly influenced parameter estimability, improved optimization results. For the maximum scenarios, the simulated salt-water dynamics showed fair agreement with the observed data (<i>r</i>² &gt; 0.7). For moderate salinity, reduced RWU was compensated by an increase of 0.01 d⁻¹, while high salinity significantly reduced this compensation to 0.002 d⁻¹ with uniform RWU of 0.004 d⁻¹.</p> Conclusion <p>The study demonstrates how different data sets contribute to accurate parameter estimation. Under high salinity, the compensation mechanism for reduced RWU was diminished, and the prolonged uniform RWU pattern suggested potential permanent root morphological changes.</p>