Evaluation of infiltration models and field-saturated hydraulic conductivity in situ infiltration tests during the dry season

Field-saturated hydraulic conductivity ( K fs ) is an important parameter used to estimate field water requirements in irrigation systems, although it is widely considered to be difficult to determine. In this study, we conducted 27 field infiltration tests with a double-ring infiltrometer to determine K fs in agricultural fields during the dry season in Myanmar. However, K fs values estimated by fitting the Philip model (Soil Sci 84(3):257–264, 1957 . https://doi.org/10.1097/00010694-195709000-00010 ) to the measured data produced negative values for many fields. The aims of this study were the following: (1) to select an infiltration model applicable to irrigable fields for which parameter K fs of the Philip model obtained negative values, (2) to identify factors causing erroneous K fs values, and (3) to present a method of obtaining valid K fs values in a case study conducted in Myanmar. Using the data obtained, the performance of five models, Philip, Swartzendruber (Water Resour Res 23(5):809–817, 1987 . https://doi.org/10.1029/WR023i005p00809 ), Brutsaert (Water Resour Res 13(2):363–368, 1977 . https://doi.org/10.1029/WR013i002p00363 ), Mezencev (Meteorol Hidrol 3:33–40, 1948 ), and Horton (Proc Soil Sci Soc Am 5:339–417, 1940 ), were assessed by examining fitting quality and estimates of K fs values. The results showed the following: (1) The Horton model was the most useful, as it showed the better fitting of parameters; (2) factors that produced negative K fs values were deformation of the infiltration curve due to the magnitude of initial infiltration caused by drying of the soil; and (3) nonnegative K fs values were obtained by rejecting an initial infiltration period, determined by improving the cumulative linearization approach of the Philip model. The revised K fs was overestimated in comparison with reference values, so a formula for applying revised K fs was presented.