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The soil sorptivity, S , which is defined as a measure of the capacity of a porous medium to absorb or desorb liquid by capillarity, is commonly estimated under laboratory conditions from upward infiltration measurements. The objective of this work is to compare different methods to estimate S from a single upward infiltration curve obtained from both theoretical and experimental soils. An additional analysis of the influence of synthetic infiltration noise on the estimation of S was also performed on the theoretical soils. Five different methods were compared: Short Time model for horizontal infiltration (ST), the Cumulative Linearization method (CL) and the Differentiated Linearization (DL) linear regressions models, Short-time (SIM) methods that use the simplified Haverkamp et al. (1994) model, and Complete-time (CIM) upward infiltration method that uses the quasi-analytical Haverkamp et al. (1994) function. Since finite soil columns were considered, the saturated hydraulic conductivity needed to estimate S with the Haverkamp et al. (1994) model was calculated from an overpressure step at the end of the water absorption process, using the Darcy's law. The methods were contrasted on four theoretical and six sieved experimental soils, ranging from sand to clay textures. Although all methods showed acceptable estimates of S on clean theoretical upward infiltration curves, the ST, SIM and CIM were the methods that gave significant ( p < 0.001) regression analysis on noisied infiltration curves, and only SIM and CIM presented a relative error < 1%. From these results we can conclude that although acceptable approaches of S were obtained with the simplest ST method, the CIM procedure was the most accurate method to estimate S in both clean and noised theoretical and experimental upward infiltration curves. [ABSTRACT FROM AUTHOR]

• A method to estimate θ s , α , n and K s from an upward infiltration is presented. • The influence of θ s, θ r and h i , on the α , n and K s optimization was studied. • It was applied to 50 mm high undisturbed cores under different soil management. • θ s and h i affected α , n and K s , and h i should be located the d θ dh ≈ 0 region. • It was sensible to different texture and structure due to the soil management. Estimation of the α and n van Genuchten (1980) parameters and the saturated hydraulic conductivity, K s , of undisturbed soil samples is critical for realistic water flow simulations in the vadose zone. Given the Latorre and Moret-Fernández (2019) method, which allows estimating K s , α and n from the inverse analysis of a single upward infiltration, the objective of this work is to advance on the theoretical understanding of this method and to apply it on undisturbed soil cores. To this end, the influence of the saturated, θ s , and residual, θ r , water content and initial soil tension, h i , on the α , n and K s optimization was first studied on synthetic soils. A procedure to simultaneously estimate θ s , α , n and K s , which consisted on optimizing α , n and K s for a range of θ s values, was proposed. To this end, α , n and K s were optimized leaving each θ s as a fixed value. The method was next applied to experimental curves measured from sieved and undisturbed soil cores of 50 mm high and diameter, sampled the last ones from three fields with different management: bare vs. under plant soil; agricultural soil under conservation vs. conventional tillage; and overburden soil from mine vs. topsoil formed by the original soil. Results showed that θ s had an important effect on α , n and K s optimization, where the minimum error within the selected θ s interval corresponded to the theoretical θ s. An important effect of h i on the optimization was also observed. However, this influence was omitted by using a h i value located in the θ r region, where d θ dh ≈ 0. Under this assumption, θ r only affected the θ s optimization, which value varied with θ r. A robust relationship (R2 = 0.99; p < 0.0001) was found between theoretical and optimized θ s , K s and α and n calculated for the synthetic soils. Thus, the method allowed estimating four of the five van Genuchten (1980) parameters. An absolute minimum was also observed when the method was applied on experimental infiltration curves. The θ s measured gravimetrically on the undisturbed samples was, on average, 8.1% higher than the optimized one. Overall, the method allowed detecting significant differences (p < 0.05) in hydraulic properties between bare and under plant soils and among tillage treatments. The large variability found in the mine's soils prevented to find significant differences within this scenario. [ABSTRACT FROM AUTHOR]