Measuring soil electrical conductivity using dual-array fusion of Wenner and Schlumberger

Accurate, real-time, and in-situ acquisition of soil electrical conductivity can provide effective data support for the precise management of agricultural production. The current-voltage four-terminal approach as an invasive technology has considerable performance in the in-situ measurement of soil electrical conductivity on a large scale. This study aims to improve the accuracy of soil electrical conductivity measured by the traditional current-voltage four-terminal approach. A systematic analysis was made to determine the constant current source and electrode spacing in the three measurement arrays. The soil bin test was carried out to explore the influence of the main factors (soil moisture content, electrode embedded depth, soil compaction, and soil texture) on the measurement accuracy of three measurement arrays at different levels. The results showed that two measurement arrays of Wenner and Schlumberger were better applied to different soil environmental conditions. The measured values of soil electrical conductivity were further used as the inputs into the model. The regression model of soil electrical conductivity was constructed using the BP neural network. The R² of the model fit was 0.99762 in the training set, and the RMSE of the model between the calculated and standard value was 0.12 μS/mm in the testing set, indicating the smaller than that of individual measurement. All RMSE values were smaller than those in the individual array measurements. The measurement device of dual-array fusion soil electrical conductivity was designed using a regression model. The components of the device included the touchable LCD display, electrode sockets, switches, differential amplifier module, constant current source module, power supply, STM32 microcontroller data acquisition module, JESTON nano, and sensor. The soil electrical conductivity was then optimized using the measured values. The working stability test showed that the standard deviation of measured data was less than 0.43 μS/mm under different soil electrical conductivity gradient conditions. The comparative field-site performance test showed that the absolute, relative error range, and RMSE of measured soil electrical conductivity were -2.1-1.8 μS/mm, -8.0%-5.8%, 0.18 μS/mm respectively. The RMSE of 0.18 μS/mm was smaller than that of the traditional individual measurement array and the commonly used soil conductivity meters in the market. The measurement device can be expected to rapidly and accurately detect the soil's electrical conductivity, indicating better working stability and higher accuracy. The finding can provide high-precision detection and technical means for the real-time in situ collection of soil information in the field.