Ks estimates using macroscopic capillary length estimated from soil hydraulic shape coefficients and Haverkamp infiltration model

In this study, we developed a new general approach to estimate the macroscopic capillary length (λ_c) using different hydraulic function models and related shape parameters, along with the Haverkamp infiltration model constant. We next applied this new approach to the van Genuchten model coupled with a Burdine condition (vGB) to estimate λ_c. Then, we applied the new λ_c computation to three different methods for estimating saturated hydraulic conductivity (K_s), and analyzed two sets of constant infiltration data: 1) an analytically generated Beerkan-type dataset and 2) constant head and Beerkan-type infiltration tests performed at the Ambarköprü Experimental Station of Blacksea Agricultural Research Institute in Samsun, Turkey. Our new approach provided accurate K_s estimates when applied to the analytical Beerkan infiltration data. The highest error was observed for a silt soil, with 30 % error for one formulation versus <15 % for the others. For synthetic coarse-textured soils such loamy sand and sandy loam, the error was <10 %. For the field data and Beerkan-type experiments, the new approach gave consistent estimates of K_s regardless of analytical interpretation. However, ANOVA analysis revealed that K_s varied between different infiltration test types, with constant head infiltrometry with 5 cm of applied water head having greater K_s values than the Beerkan tests (p < 0.05). Estimated K_s values also differed between land use types (p < 0.01), with a maize field having significantly greater K_s compared to a soybean field. Overall, we conclude that the proposed approach represents an efficient and appropriate method for characterizing point-scale saturated hydraulic conductivity, so long as experimental artifacts such as ring insertion deep and preferential flows are considered.