Inverse estimation of unsaturated soil hydraulic and solute transport properties has thus far been limited mostlyto analyses of onedimensional experiments in the laboratory, often assuming steadystate conditions. This is partly becauseof the high cost and difficulties in accurately measuring and collecting adequate fieldscale data sets, and partly becauseof difficulties in describing spatial and temporal variabilities in the soil hydraulic properties. In this study, we estimated soilhydraulic and solute transport parameters from several twodimensional furrow irrigation experiments under transientconditions. Three blockedend furrow irrigation experiments were carried out, each of the same duration but with differentamounts of infiltrating water and solutes resulting from water depths of 6, 10, and 14 cm in the furrows. Two more experimentswere carried out with the same amounts of applied water and solute, and hence for different durations, on furrows with waterdepths of 6 and 10 cm. The saturated hydraulic conductivity (Ks) and solute transport parameters in the physical equilibriumconvectiondispersion (CDE) and physical nonequilibrium mobile immobile (MIM) transport models were inverselyestimated using the LevenbergMarquardt optimization algorithm in combination with the HYDRUS2D numerical code. Soilwater content readings, cumulative infiltration data, and solute concentrations were used in the objective function duringthe optimization process. Estimated Ks values ranged from 0.0389 to 0.0996 cm min1, with a coefficient of variation of 48%.Estimated immobile water contents (.im) were more or less constant at a relatively low average value of 0.025 cm3 cm3,whereas the firstorder exchange coefficient (.) varied between 0.10 and 19.52 min1. The longitudinal dispersivity (DL)ranged from 2.6 to 32.8 cm, and the transverse dispersivity (DT) ranged from 0.03 to 2.20 cm. DL showed some dependencyon water level and irrigation/solute application time in the furrows, but no obvious effect was found on Ks and other transportparameters, most likely because of spatial variability in the soil hydraulic properties. Agreement between measured andpredicted infiltration rates was satisfactory, whereas soil water contents were somewhat overestimated, and soluteconcentrations were underestimated. Differences between predicted solute distributions obtained with the CDE and MIMtransport models were relatively small. This and the value of optimized parameters indicate that observed data weresufficiently well described using the simpler CDE model, and that immobile water did not play a major role in the transportprocess.
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Abbasi et al. (2003) studied this question.