Laboratory Evaluation of a Low-Cost Soil Moisture and EC Sensor in Different Soil Types

Soil moisture and electrical conductivity (EC) measurements are vital for improving water usage efficiency and monitoring soil salinization. Water stress and groundwater salinity are the twin problems associated with excessive groundwater extraction and irrigation with saline water. Small and marginal farmers are the majority in India and require low-cost sensors for measuring soil moisture and EC. This work evaluates the performance of a low-cost capacitance-resistive sensor for soil moisture and EC measurement in different soil types. The results show that bulk EC and bulk density of the soils moderately affect the sensor output (oscillation frequency) for moisture measurement. The multilinear regression models developed using experimental data for moisture have an R² of 0.93, which is at par with the commercial sensors reviewed by researchers. Bulk EC variation with moisture showed significant variation with soil type due to differences in the salinity levels of soil samples. Therefore, the field devices require standard EC thresholds for salinity similar to laboratory standards.