Development of a Portable Acoustic Soil Moisture Detection Device with Temperature Compensation

Soil moisture is one of the key factors in agricultural production. Efficient and accurate acquisition of the soil moisture content (SMC) is essential for ensuring the proper functioning of agricultural activities. However, conventional SMC detection methods fail to meet the basic requirements for moisture detection in field environments, including real-time efficiency, cost effectiveness, and reliability. The aim of this study was to evaluate the effectiveness of a portable acoustic detection device with temperature compensation for soil moisture detection in field environments. A soil acoustic measurement and data acquisition system was developed in this study, utilizing the pulse transmission method while considering the impact of temperature on acoustic velocity measurements. A temperature gradient of 5 °C was set within a range of 5–40 °C, while maintaining a relative humidity of 50%. The relationships among the SMC, soil temperature, and acoustic velocity were experimentally analyzed, and a temperature-compensated SMC acoustic prediction model was developed via multivariable nonlinear regression. Through hardware selection, software development, and system integration, a portable acoustic soil moisture detection device with temperature compensation was successfully developed. To assess the performance of the device, tests were conducted to evaluate its acoustic velocity detection performance, waterproof capability, and effective detection range. A 25-day field experiment was carried out in an orchard, during which the soil temperature ranged from 9.0 °C to 24.5 °C, and the results indicated that the average relative error between the device's SMC measurements and the oven-drying method was 5.64%. When the SMC exceeded 0.275 g/g, the maximum relative error was 3.91%.