Double-ring and Tension Infiltrometer Measurements of Hydraulic Conductivity and Mobile Soil Regions1

1. Article submitted on Sept./2010 and accepted for publishing on Aug./2011 (n° PAT 11376/ DOI: 10.5216/pat.v41i3.11376). 2. Helmholtz Centre for Environmental Research (UFZ), Department of Soil Physics, Halle, Germany. E-mail: [email protected]. 3. Universidade Federal de Goiás, Escola de Agronomia e Engenharia de Alimentos, Goiânia, GO, Brazil. E-mail: [email protected]. 4. Martin-Luther Universität, Halle, Gemany. E-mail: [email protected]. 5. Johann Heinrich von Thünen-Institut, Institut für Agrarrelevante Klimaforschung, Braunschweig, Germany. E-mail: [email protected]. 6. University of Rostock, Institute for Land Use, Faculty for Agricultural and Environmental Sciences, Rostock, Germany. E-mails: [email protected], [email protected]. 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 Ks 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 TIsand (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 Ks 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 TIsand. 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 Ks 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.