Soil moisture (SM) varies greatly in the soil profile. We developed a low-cost sensor for SM monitoring at three vertical depths. The sensor function was based on dielectric theory to monitor SM. Three linear calibration models were established using different soils. The sensor for each depth showed acceptable statistics of validations. The linear fit coefficient of determination (R2) ranged from 0.95 to 0.99. Root mean square error (RMSE) ranged from 1.35 to 4.30. The sensor performed consistently for at least 4 months, and is suitable for continuous monitoring of in situ SM and irrigation scheduling.
dielectric sensor; soil moisture; vertical depths
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