Smart Irrigation: IoT Soil Sensors and Automated Watering

How it works

Conventional irrigation runs on a schedule: a valve opens for a set time whether or not plants need water. Smart irrigation decides based on data:

1. Sensors in the soil measure moisture at root depth.
2. Data travels wirelessly to a gateway and on to a cloud or local system.
3. The system compares moisture with crop thresholds and takes the weather forecast into account.
4. A controller opens valves for the right zone and starts the pump.
5. A flow meter records how much water went to each zone.

The operator sees everything in a web dashboard or mobile app and can step in manually.

Soil moisture sensors

Practical rules:

• install sensors at two or three depths: in the active root zone and below it, to see whether water is draining too deep;
• choose locations typical for the zone, not the field edge or a low spot;
• with drip irrigation, place the sensor near an emitter, inside the wetted zone;
• calibrate for your soil type, otherwise absolute values will be off.

Controllers and drip automation

Drip systems are the best candidates for automation because water is delivered precisely by zone. You need:

• solenoid valves for each irrigation zone;
• a controller with a wireless module or wired connection to the valves;
• pump control and pressure monitoring;
• flow meters on the main line or per zone;
• optionally fertigation — dosing fertilizer with the water.

The irrigation logic can be simple:

if soil_moisture < lower_threshold and rain_forecast_mm < rain_skip_mm:
    open_valve(zone, duration=calc_duration(zone))
elif soil_moisture > upper_threshold:
    close_valve(zone)

Thresholds are set by the agronomist for each crop and growth stage. Build in safeguards: a maximum valve run time, an emergency stop on pressure loss or leaks, and a manual mode.

Weather data

Soil moisture shows the current state; weather shows what is coming. Useful data:

• rain forecast — skip irrigation before rain;
• evapotranspiration (ET) — how much water evaporates from the field and plants; it is calculated from temperature, humidity, wind and solar radiation, using the method described in the FAO-56 guidelines;
• frost and heat — adjust the irrigation regime.

The source is either your own weather station on the farm or a weather API. An on-site station reflects the field's microclimate more accurately.

Connectivity in the field

The main practical challenge is getting data out of a field with no power outlets and often weak mobile coverage.

Sensors usually run on batteries and report every few minutes, while the gateway and controller run on mains or a solar panel with a battery. Test coverage in the actual field before buying.

Calculating water savings

Without metering, savings are just a feeling. How to calculate:

1. Install flow meters and record a baseline season: how much water each zone used under the old regime.
2. Compare it with a season on smart irrigation: savings = baseline volume − new volume.
3. Normalize to cubic meters per hectare to compare zones of different size.
4. Account for weather: comparing a hot year with a cool one directly is misleading. Normalizing by evapotranspiration helps.
5. Track water productivity too — yield per cubic meter. Saving water while yield drops is not a win.
6. Add indirect effects: pump electricity, fertilizer with fertigation, labor.

The most reliable approach is comparing two similar zones in the same season: one automated, one on the old regime.

Common mistakes

• One sensor for a large, non-uniform field.
• No sensor calibration or maintenance.
• No protection against a valve stuck open.
• No flow meters, so there is nothing to prove the result.