Smart Agriculture (Soil Moisture)

Theory: Conductivity & Soil Moisture

From Sensing Air to Sensing Earth

So far, we have learned to sense conditions in the air around us (light, temperature, humidity, gas). Now we're expanding our sensing capabilities to measure conditions in soil - the foundation of agriculture! The soil moisture sensor is our gateway into precision agriculture, where technology helps farmers optimize water usage, improve crop yields and conserve resources. This sensor doesn't measure water directly; instead, it measures electrical conductivity, which changes dramatically between dry and wet soil.

How Conductivity Works

Conductivity is the ability of a material to conduct electricity. Pure water is actually a poor conductor, but soil water contains dissolved minerals (salts, nutrients) that make it conductive. The soil moisture sensor has two metal prongs that act like an open circuit. When inserted into dry soil, almost no current flows between the prongs - high resistance. When inserted into wet soil, water creates a conductive path between the prongs - low resistance. By measuring this resistance change, we can determine moisture levels!

Understanding the Sensor Reading

The soil moisture sensor outputs an analog voltage that varies with moisture content. Your MakerBuddy reads this voltage and converts it to a percentage or numerical value. Typical readings:

• Dry soil (0-30%): Very little conductivity, high resistance, low sensor reading
• Moist soil (30-60%): Moderate conductivity, comfortable for most plants
• Wet soil (60-100%): High conductivity, low resistance, high sensor reading
• In water (100%): Maximum conductivity, sensor reads highest value

Calibrating the Moisture Percentage

The dashboard converts the sensor's raw analog reading into a 0–100% moisture level. Because sensor modules can report either higher or lower raw values as moisture increases, do not guess the direction or reuse someone else's numbers. Calibrate the two endpoints with the same probe and soil used in the project.

1. Open the Soil Moisture card and select its calibration settings.
2. Hold the probe in dry soil (or air for a baseline), wait for the reading to settle, and save that raw value as Dry.
3. Place the probe in thoroughly wet soil, wait for the reading to settle, and save that raw value as Wet.
4. Return to the dashboard and test dry, damp, and wet soil. If the percentage moves in the wrong direction, repeat both endpoint measurements and check that the probe is connected correctly.

Why Soil Moisture Matters

Plants need water to survive, but too much or too little causes problems. Overwatering wastes water and can rot roots. Underwatering stresses plants and reduces growth. Smart agriculture uses soil moisture sensors to water only when needed, saving billions of gallons of water globally while improving crop health. Farmers use networks of these sensors across fields to create moisture maps, identifying dry spots that need irrigation and wet spots that need drainage.

Real-World Applications

Soil moisture sensors power automated irrigation systems in farms, vineyards and golf courses. Smart gardens use them to water plants automatically via app control. Greenhouses maintain optimal growing conditions. Even NASA uses soil moisture sensors on Mars rovers to search for water! Urban gardens, vertical farms and home plant monitors all rely on this technology to optimize water usage and plant health.

Hands-On Activity: Soil Moisture Testing

Activity Duration: 20-25 minutes

Students will connect the soil moisture sensor, test it in various conditions (dry, moist, wet) and observe how conductivity changes with water content. This hands-on exploration demonstrates the relationship between moisture and electrical resistance.

Step-by-Step Instructions:

1. Identify the Sensor: Locate the soil moisture sensor - it has two metal prongs (electrodes). The prongs should be clean and free of corrosion.
2. Locate the Connector: Find the connector labelled 32 on your MakerBuddy IoT Board.
3. Open the Dashboard: Navigate to your MakerBuddy web interface and locate the Soil Moisture sensor card showing the current reading (usually 0-100%).
4. Air Test (Baseline): Hold the sensor in the air, not touching anything. Record this "dry" baseline value (From Soil Moisture Calibration Popup, Save as dry Calibration) - it should be very low (near 0%) since air doesn't conduct electricity.
5. Wet Test: Dip just the metal prongs (not the circuit board!) into a cup of water. The reading should jump to near maximum (90-100%) (From Soil Moisture Calibration Popup, Save as wet Calibration).
6. Moist Soil Test: Add a small amount of water to the soil and mix it. Insert the sensor again. Watch the reading increase as moisture creates conductive paths. Record the value.
7. Recovery Test: Remove the sensor from water and dry it with a paper towel. Watch the reading drop back to baseline. This demonstrates the sensor's responsiveness.

What Students Should Observe:

• Clear difference between dry (low reading) and wet (high reading) conditions
• Gradual increase in reading as moisture increases
• Instant response when sensor touches water (high conductivity)
• Reading drops when sensor is removed and dried
• Sensor values update in real-time on the dashboard
• Metal prongs must be inserted into soil/water for accurate readings

Challenge

Key Takeaways