Investigation of thermal and hydraulic properties of sandy-loam soils under diverse land-use systems

Abstract

Information about soil thermal properties (STPs) based on different land-use patterns will support optimum utilization of ground-based thermal energy. This study quantified in-situ soil thermal properties (STPs) and some associated hydraulic parameters under different land practices in parts of Abeokuta, Southwest Nigeria. Five sampling points for thermal and hydraulic properties were established within 80 m by 40 m on each of grassland (GL), oil palm plantation site (OPS), football pitch (FP), dumpsite (DS), automobile mechanic workshop (AMW), and block making site (BMS). Thermal properties were measured in situ using KD2 Pro Thermal Properties Analyzer while topsoil hydraulic parameters were determined using standard laboratory procedures. Pearson's correlation and analysis of variance (ANOVA) were employed to determine the interrelationships and variations of measured STPs among the diverse land use patterns. Results of assessed STPs indicated that the average values of thermal conductivity (λ_s) were higher in AMW and DS (1.77 and 1.53 s W/mK, respectively) relative to that of other land uses (0.37- 0.79 W/mK). In the investigated land uses, highest and lowest mean values of thermal diffusivity (TD) (0.850 and 0.209) were recorded in AMW and GL, respectively. The OPS had lowest mean specific heat capacity (C_S ) (1.381 MJ/m³ K) and bulk density (BD) of ≈1.5 sMg/m³ while DS topsoil had maximum value of average C (3.930 MJ/m³ K) but least BD of 1.17 Mg/m³ . The highest values of average thermal admittance (µ_s), saturated hydraulic conductivity (K_sat ) and soil moisture content (MC) were observed in FP while least values of µ_s, K_sat and MC were recorded in AMW. The mean thermal resistivity (TR) values in DS and AMW were within the 90 °C-cm/W recommended for safe cable engineering practices. Correlation analysis revealed strong direct relation between λ_s  and TD while ANOVA results showed that most of the measured STPs were significantly different (p<0.05) among the six land-use systems. Most of the measured STPs can be regarded as dynamic characteristics that are intensely swayed by land uses.