The objectives of this study were to (i) investigate the estimability of hysteretic hydraulic parameters from the data of a field irrigation experiment and (ii) to optimize the estimable parameters by comparing two scenarios. The soil and rainfall data are from an irrigation experiment carried out by subproject A4 of the SFB/TRR 38 at the BTU Cottbus. HYDRUS software was used to simulate the soil water movement. Estimability analysis was based on sequentially calculating a sensitivity coefficient matrix to classify parameter estimability. The results of the estimability analyses showed that the pressure heads at the soil surface contained more information content for parameter calibration than the one measured greater depth. The fitting between simulated values and data was slightly improved when the model accounts for the hysteresis phenomenon.