Response of the TEROS 12 Soil Moisture Sensor under Different Soils and Variable Electrical Conductivity

Area of Science:

• Soil Science
• Environmental Monitoring
• Electrical Engineering

Background:

• Accurate measurement of soil properties is crucial for environmental and agricultural applications.
• Electromagnetic sensors like TEROS 12 are widely used for soil water content and electrical conductivity.
• Sensor performance can be affected by soil type, water content, and solution conductivity.

Purpose of the Study:

• To evaluate the performance of the TEROS 12 electromagnetic sensor under various soil conditions.
• To assess the sensor's accuracy in measuring volumetric soil water content (θ) and bulk electrical conductivity (σb).
• To investigate the influence of soil type and electrical conductivity of the soil solution (ECw) on sensor readings.

Main Methods:

• Laboratory experiments were conducted using six different porous media.
• TEROS 12 sensor performance was tested across a range of soil water content (θ) and electrical conductivity (ECw) levels.
• A prototype device with a low-cost microcontroller and adaptation circuits was developed for sensor integration.

Main Results:

• TEROS 12 apparent dielectric permittivity (εa) readings were lower than Topp's relationship, particularly in coarse soils at high water content.
• A strong linear relationship was found between measured soil water content (θm) and εa^0.5 (R² > 0.869), but linearity decreased with increasing bulk EC (σb).
• The multipoint calibration method (CAL) provided the most accurate results, with εa degrading at σb < 2.5 dS/m and showing a linear relationship with σb.

Conclusions:

• The TEROS 12 sensor's accuracy is influenced by soil type and electrical conductivity.
• Calibration methods significantly impact measurement accuracy, with multipoint calibration being superior.
• Understanding the relationship between εa, σb, and soil properties is essential for reliable soil monitoring.