Warning. This technology has not yet been validated, because it is not yet ready to scale.

Soil Moisture Monitoring: Wetting Front Detector

Wetting Front Detector

The Wetting Front Detector (WFD) is a simple, mechanical device used in irrigation to monitor how deeply water has penetrated into the soil root zone. It consists of a specially shaped funnel buried in the soil, connected to a float mechanism and an indicator flag aboveground. When water from irrigation or rain moves down through the soil and reaches the detector's funnel, it collects in a small reservoir, triggering the float to raise the flag. This indicates that the soil at that depth is saturated and irrigation can be stopped to avoid overwatering.

The WFD requires no wires, batteries, or electronic components. It also retains a small sample of soil water, which can be extracted and tested for salinity or nutrient levels using simple field tools. By showing the depth of the wetting front, the device helps farmers and irrigators visualize soil moisture, optimize irrigation scheduling, save water, and improve crop water productivity.

This technology is not yet validated.

Scaling readiness: idea maturity 8/9; level of use unknown

Adults 18 and over: Positive medium

The technology does not have a negative impact on people, nor does it have any adverse environmental effects on those who use it.

The poor: Positive low

It is affordable

Under 18: No impact

The technology does not affect people

Women: Positive medium

It is easy to use by all gender

Climate adaptability: Highly adaptable

It is adaptable to irrigated areas across different ecologies.

Farmer climate change readiness: Significant improvement

The device enhances water productivity by reducing over irrigation and improved nutrient use efficiency.

Environmental health: Greatly improves environmental health

Soil quality: Does not affect soil health and fertility

Water use: Much less water used

It reduces irrigation water use

Biodiversity: Not verified

Problem

Over-irrigation: Prevents applying too much water, reducing water waste and avoiding waterlogging and crop damage.
Under-irrigation: Helps identify when insufficient water is applied, preventing crop stress and yield loss.
Invisible soil moisture dynamics: Makes soil water movement visible and understandable to farmers, aiding better irrigation decisions.
Nutrient and salt monitoring: Enables sampling of soil water to monitor nutrient levels and salinity for improved fertilizer and salt management.
Inefficient water use: Guides more precise irrigation scheduling to increase water productivity and save energy and labor.
Uneven irrigation: Detects soil moisture uniformity issues, helping manage irrigation for more consistent moisture distribution.

Solution

Visual irrigation guidance: Provides clear visual cues on soil moisture depth to optimize water application.
Simple, power-free operation: Eliminates need for electricity or complex tools, making it accessible globally.
Accurate irrigation scheduling: Signals when soil is optimally wet, preventing both over- and under-watering.
Soil water sampling: Allows extraction of soil water for nutrient and salinity testing to guide fertilizer use.
Versatile across systems: Suitable for drip, sprinkler, and furrow irrigation methods.
Water and energy efficiency: Helps save water and reduce labor by improving irrigation timing and uniformity.
Enhanced farmer learning: Offers immediate feedback to support better irrigation decision-making and practice improvement.

Key points to design your project

Wetting Front Detector (WFD) is a practical and innovative technology that enables farmers to visually monitor how deeply water infiltrates into the soil root zone during irrigation or rainfall. By detecting the "wetting front" in the soil, the WFD helps prevent both over-irrigation, which wastes water and causes waterlogging, and under-irrigation, which can stress crops and reduce yields. The device also collects a small soil water sample, allowing measurement of salinity and nutrient levels to guide fertilizer and soil health management. Designed with no wires, batteries, or electronics, the WFD is simple, robust, and highly suitable for diverse agricultural settings.

To integrate the WFD technology effectively into your agricultural projects, please consider the following key steps:

Estimate Quantity and Costs: Calculate the number of detector units needed. Typically, two detectors per field are used (at shallow and deep root-zone depths). Each box containing two pairs of detectors costs approximately USD 36, excluding freight and taxes.
Procurement and Logistics: Account for supply location, shipping, import clearance, taxes, and delivery costs to ensure uninterrupted availability at the project sites.
Training and Support: Plan for training local extension agents and farmers on installation, interpretation of indicators, maintenance, and data use. Include costs for ongoing support post-training to enhance adoption and sustained use.
Communication and Outreach: Develop educational materials such as flyers, demonstration videos, and radio messages to broaden outreach and facilitate farmer understanding of WFD benefits and operation.
Installation Guidelines: WFDs should be installed at specific depths based on irrigation type (e.g., 30–50 cm for drip irrigation). Proper placement ensures accurate wetting front detection and reliable irrigation scheduling.
Complementary Practices: For increased impact, consider combining WFD use with improved crop varieties, soil nutrient management, precision irrigation techniques, and digital advisory tools.
Partnerships for Implementation: Collaborate with agricultural research institutes, extension services, and local agro-dealers to enable technology transfer, technical advice, and sustainable scaling.

The WFD technology empowers farmers to make informed irrigation decisions, maximizing water use efficiency, boosting crop yields, reducing environmental risks, and contributing to resilient and climate-smart agriculture aligned with global sustainability goals. Incorporating this tool into your projects establishes a foundation for sustainable water management and equitable agricultural development.

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Range of water savings

IP

Open source / open access

Countries with a green colour: Tested & adopted
Countries with a bright green colour: Adopted
Countries with a yellow colour: Tested
Countries with a blue colour: Testing ongoing

Countries where the technology is being tested or has been tested and adopted
Country	Testing ongoing	Tested	Adopted
Ethiopia	–No ongoing testing	Tested	Adopted
Ghana	–No ongoing testing	Tested	Adopted
South Africa	–No ongoing testing	Tested	Adopted
Zimbabwe	–No ongoing testing	Tested	Adopted

This technology can be used in the colored agro-ecological zones. Any zones shown in white are not suitable for this technology.

Agro-ecological zones where this technology can be used
AEZ	Subtropic - warm	Subtropic - cool	Tropic - warm	Tropic - cool
Arid	–	–		–
Semiarid	–	–		–
Subhumid	–	–		–
Humid	–	–	–	–

Source: HarvestChoice/IFPRI 2009

The United Nations Sustainable Development Goals that are applicable to this technology.

Goal 2: zero hunger

Goal 12: responsible production and consumption

Goal 13: climate action

Assemble the Detector
- Join the base piece to an extension tube by dipping in hot water to soften plastic, then twist to lock.
- Add additional extension tubes if deeper placement is required.
- Insert foam floats into the extension tubes, ending with the float marked with a blue dot.
- Fit the indicator cap onto the top and attach the green flexible tubing at the bottom.
Test for Leaks
- Fill the funnel with water using a syringe; the float should rise and hold up the indicator flag with no leaks at joints.
- Release water through the flexible tube and reset the float by tapping the indicator down.
Dig Installation Hole
- Use two augers or a shovel and trowel to dig two holes: a wide hole for the funnel and narrow hole for the extension tube.
- Keep soil layers separate to return them in original order.
Add Filter Sand and Insert Detector
- Pour some filter sand into the funnel to cover the locking ring by at least 1 cm.
- Place the detector vertically into the hole at the desired depth based on irrigation method (e.g., 30-50 cm for drip systems).
- Fill gently with soil from the same layer, firm lightly around the funnel, ensuring the flexible tube extends above ground.
Backfill and Level Soil
- Return all soil layers carefully to avoid compacting.
- Leave a slight hump over the detector site that settles to soil level to prevent water run-off away from the detector.
Activate the Float
- Apply water (20 liters or more for deep installations) to trigger the float indicating the wetting front has reached the detector depth.
Read Indicator
- Observe the flag position (up or down) on shallow and deep detectors to interpret soil water status and decide irrigation adjustments.
Maintenance
- Test float mechanism and filter every few months by injecting water through the tube and checking the float's response.
- Check for leaks regularly and clean or disassemble floats if needed.

Downloads

Soil Moisture Monitoring training manual.pdf (PDF, 474.75 KB)

Last updated on 28 October 2025

International Water Management Institute
Adebayo Oke

Commodities

Vegetable crop

Sustainable Development Goals Details ›

Subcategory

Water management

Value chain step

Pre-production

Solution

over irrigation under irrigation inefficient water use nutrient monitoring salt monitoring

Toolkits

IWMI technologies toolkit

Tested/adopted in Details ›

Countries with a green colour: Tested & adopted
Countries with a bright green colour: Adopted
Countries with a yellow colour: Tested
Countries with a blue colour: Testing ongoing

Where it can be used Details ›

This technology can be used in the colored agro-ecological zones.

Target groups

Farmers

IWMI technologies toolkit

Soil Moisture Monitoring: Wetting Front Detector

Problem

Solution

Key points to design your project

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