Evaluation of a novel electromechanical system for measuring soil bulk density

Digital electromechanical system (DES), consisting of automatic sample collection, on-site microwave drying and weighing is a novel technology for soil bulk density measurement. The study investigates the potential use of the DES for in situ measurement of bulk density, and evaluates the thermal efficiency and specific energy consumption during measurement. The experiment was conducted in eight fields with different soil textures of a silty clay, loamy, clay loam, silty loam, and silty clay loam, at three soil depths of 0–10, 10–20 and 20–30 cm. Data management and analysis used include split-plot with systematic plot arrangement. Least significant difference (LSD) analyses at 0.05 confidence were applied to compare between the mean of groups. Results indicate that the dry bulk density (ρb) and wet bulk density (ρn) of soil can be measured successfully by the DES, and accuracy of measurement is significantly influenced by soil texture type and depth. The largest microwave drying time of 37 min was needed for the silty clay soil, while 17 min was the lowest drying time recorded for the sandy loam soil. Thermal efficiency was increased with increased soil depth for different soil textures and moisture content strongly influenced the thermal efficiency. Furthermore, the specific energy consumption decreased with increased soil depth for different soil textures. An inversely proportional relationship between specific energy consumption and soil depth was found and was attributed to soil moisture evaporation. A significant relationship between soil ρb and microwave penetration depths in different soil textures was demonstrated, which was due to changes in soil dielectric constant.