DOUBLE-RING AND TENSION INFILTROMETER MEASUREMENTS OF HYDRAULIC CONDUCTIVITY AND MOBILE SOIL REGIONS

Abstract

There are several field methods and techniques for measuring Ks. In this study, double-ring (DI) and tension infiltrometer (TI) infiltration techniques were combined with dye tracer application and compared for estimating K_s and the mobile soil fraction on a structured sandy loam soil (Gleyic Luvisol), in Rostock, Germany. Water was infiltrated into soil by using three methods: DI, TI (without contact with sand), and TI_sand (with contact with sand), until steady-state conditions were obtained. At different positions, three pulse depths of 25 mm, 50 mm, and 100 mm, with a 2 g L^-1 Brilliant Blue (BB) FCF dye solution, were used. The results showed variable K_s values for DI of 820-2,020 cm d^-1, which were 7 to 13 times higher, when compared to TI values, and 12 to 33 times higher than for TI_sand. For the 25 mm and 50 mm BB applications, the mobile (dye-stained) soil regions constituted up to 60% in the top 25 cm and varied little, when considered the infiltration methods. Only the 100 mm application, using the DI, yielded significant BB displacement into the subsoil. Hence, both K_s values and their corresponding dye pattern depended on the boundary conditions. For DI, more than 90% of the dye was constrained below the infiltration area, revealing that flow was essentially vertical.