Hydraulic Conductivity and Infiltration of Soils of Tropical Rain Forest Climate of Nigeria

Abstract

Hydraulic conductivity (K_θ) is the single most important hydraulic parameter for flow and transport-related phenomena in soil. In this study, the effects of soil moisture contents, soil bulk density (BD), total porosity (PT), soil water holding capacity (WHC), organic matter content, and cation exchange capacity (CEC) on hydraulic conductivity of various sized aggregates of horizon A (0 – 20 cm soil layer) in five major cities (Ibadan, Ife, Akure, Owo and Ado-Ekiti) of the tropical rain forest zone of Nigeria was investigated. Hydraulic conductivity was determined by a steady-state flow using an infiltration device (mini-disk infiltrometer). Suction rates of 2 cm s^-1, 3 cm s^-1, and 4 cm s^-1 were chosen at different locations on the fields for the infiltration measurement and subsequent estimation of soil hydraulic conductivity. At 2 cm s^-1 suction rate, the mean value of K_θ ranged from 0.0022 ± 0.001 cm s ^-1   to 0.00071 ± 0.0004 cm s ^-1. The highest and lowest mean bulk densities 1.5 g cm^-3 and 1.33 g cm^-3 were observed in soils of Ife and Akure, respectively. Similarly, mean total porosity values ranged between 0.44 cm³ cm^-3 and 0.5 cm³ cm^-3. Statistical relationship between the total porosity and hydraulic conductivity gave a high correlation coefficient, r = 0.94 at p < 0.05. The correlation coefficient (r) between water holding capacity and hydraulic conductivity was 0.95. Results shows that Soil physical properties such as bulk density, total porosity and water holding capacity affect water infiltration characteristics of soils of the study area.