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 soil moisture and EC measurement. This work evaluates the performance of a low-cost device for soil moisture and EC measurement in different soil types. In soils with low EC and uniform particle size distribution, the sensor output is linear with
$\mathrm{R}^{2}$
of 0.94-0.96. However, in most field soils, the linear-fit
$\mathrm{R}^{2}$
varies from 0.74 to 0.84 depending on soil type, soil EC, and bulk density. Since the bulk EC and bulk density vary with soil moisture, the Pearson correlation test shows that bulk EC and bulk density have a moderate correlation with sensor output (oscillation frequency) for moisture measurement. So the impact of bulk EC and bulk density on soil moisture measurement cannot be ignored.