Types of Soil Moisture Sensors

  • Resistive (Conductivity-Based) Sensors:

    • How They Work:

      • Water in the soil conducts electricity between two metal probes.

      • More water leads to lower electrical resistance.

    • Limitations:

      • Probes are in direct contact with soil, making them prone to corrosion—especially in salty soil—which can cause false high moisture readings.

  • Capacitive (Dielectric-Based) Sensors:

    • How They Work:

      • They detect changes in the soil’s dielectric constant without exposing metal probes directly to the soil.

    • Advantages:

      • More resistant to corrosion and provide more accurate readings in saline or high-humidity environments.

Effects of Salinity and Corrosion

  • Salinity Impact:

    • Resistive Sensors: Salt in soil increases conductivity, leading to false high moisture readings. Accelerates corrosion on metal probes.

    • Capacitive Sensors: Less affected by salts, ensuring more reliable readings.

  • Corrosion Overview:

    • The gradual degradation of metal due to chemical reactions with the environment (e.g., rusting).

    • High costs in infrastructure maintenance; a key factor in sensor durability.

In-Class Experiment: Soil Moisture Monitoring

  • Objective:

    • Compare performance between resistive and capacitive sensors across different soil types (dry air, sandy, clay, loamy, and salty soil).

  • Materials Needed:

    • Arduino R3 Uno, both sensor types, soil samples, water, containers, and data logging tools (Excel/Google Sheets)

Discussion and Real-World Applications

  • Key Questions:

    • How do different soil types affect sensor accuracy?

    • What role does salinity play in sensor performance?

  • Real-World Connections:

    • Smart agriculture (precision irrigation)

    • Coastal flood monitoring and infrastructure management

    • Corrosion prevention in engineering