We present an accurate, simple and inexpensive laboratory method to estimate four of the five van Genuchten (1980) parameters (θs, Ks, α and n) from the inverse analysis of an upward infiltration curve. The method can be applied to any kind of soil textures and undisturbed samples collected with the 5-cm long cores commonly employed for soil bulk density determinations (Latorre and Moret-Fernández 2019; Moret-Fernández et al. 2020). The initial soil tension, hi, used in the method, which is located in the θr region, allows stocking the soils samples under atmospheric room conditions.
Taking θr as a measurable data, an objective function Q(α, n, Ks) is defined and minimized for a sequence of θs values within the [θs_e, θs_e + 3%] interval, where θs_e is the experimental saturated water content calculated from the total infiltrated water (Moret-Fernández et al., 2020). Q(α, n, Ks) represents the difference between the upward infiltration curves simulated with HYDRUS-1D and experimental infiltration data (Moret-Fernández et al., 2020)
where N is the number of measured I values, Ie(ti) and Is(ti) are specific measurements at time ti. A modified random adaptive step optimization method (ASSRS) was employed (Latorre and Moret-Fernández et al., 2019). In our case, a -9 109 cm of soil tension, the maximum allowed by HYDRUS-1D, was employed as hi value.
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References
Latorre, B., Moret-Fernández, D. 2019. Simultaneous estimation of the soil hydraulic conductivity and the vanGenuchten water retention parameters from an upward infiltration experiment. Journal of Hydrology 572, 461–469.
Moret-Frnández, D., Latorre, B., López, M.V., Pueyo, Y., Tormo, J., Nicolau, J.M. 2020. Hydraulic properties characterization of undisturbed cores under different soil managements. Catena ...