Abstract

Mini-infiltrometer for determining soil sorptivity, hydro-repellency and other hydraulic properties of soil using water and other forms of fluid was designed and developed. It was made of quality pyrex glass tubes and calibrated to metric standard after manufacture. The component of the mini-infiltrometer include: the infiltrometer tube, which bears a porous sponge at the tip for moisture metering into soil samples, ‘U’ tube manometer, capillary tube, rubber hose (joints) and glass valves. Experimental tests were conducted on the manufactured mini-infiltrometer to determine soil sorptivity to water by the steady state flow on soil samples obtained at depths 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 m from four different locations at the Federal University of Technology, Akure (FUTA) in the southwestern part of Nigeria. The experimental procedures involve measurement of water uptake at negative pressure heads from a small circular porous membrane in contact with the surface of the aggregates. Soil samples from location L2, which were predominantly clay, had the lowest mean total porosity (0.12 ± 0.02)%, and were characterized by low mean value of sorptivity (0.406 ± 0.06) mms^-1/2. Soil sorptivity to water increased from the surface soil layer (10 cm) to the 20 cm depth with values 0.801(±0.04), 0.753(±0.15) and 0.777(±0.04) in soil samples from locations L1, L3 and L4, respectively, except for aggregates from location L2, which exhibited reductions in sorptivity from the 10 cm to the 70 cm soil layer. The successive reduction in sorptivity of L2 with depth is an indication of the influence of reduced porosity of samples as clay content increased with depth. High coefficients of correlation r² = 0.98, 0.97, 0.97 and 0.88 at p = 0.05 were obtained from the relationship between the manufactured mini-infiltrometer and standard disk infiltrometer. The results show that soil hydraulic and sorptivity properties are dependent on soil aggregate composition, total porosity and organic matter content.

Key words: Infiltrometer, sorptivity, porosity, infiltration, bulk density.