The disc infiltrometer has been established as a field device for in situ measurements of unsaturated infiltration under tensions. Several methods have been developed for calculating hydraulic properties based on infiltration data from the disc infiltrometer. The method by Zhang (1998) has the advantage in using infiltrometer data measured in a relatively short time period to estimate soil hydraulic properties. In this study, we improved this method by replacing the piecewise linear approximation of hydraulic conductivity function (K(h )), which results in overestimated macroscopic capillary length, with the exponential form of K(h). An efficient and accurate iteration procedure was introduced to solve the highly nonlinear equations of the improved method. An experiment was conducted in a large field to measure infiltration processes at various locations with different sizes of disc infiitrometers under different tensions. Based on the infiltration data, the improved method and three other methods in the literature were utilized to estimate soil hydraulic conductivities at different tensions and macroscopic capillary length. Compared with the three methods, the proposed method provided more accurate and stable estimations of the hydraulic conductivity and macroscopic capillary length, using infiltration data collected at short experiment periods within 20 min. Key words: Soil hydraulic conductivity, disc infiltrometer, infiltration rate
Three‐ and four‐term approximate expansions of the Haverkamp formulation to estimate soil hydraulic properties from disc infiltrometer measurements
