Watermark Sensors

Technology Explainer

Watermark sensors, also known as granular matrix sensors, measure soil water tension aka matric potential. They consist of a granular matrix embedded between two electrodes. As soil moisture changes, the electrical resistance in the granular matrix changes, providing an estimate of soil moisture.

Accuracy

The accuracy of Watermark sensors is not very good, they do not give the same accuracy as TDT of TDR sensors.

Furthermore,Watermark sensors are very slow to react to changes in the soil moisture content, hence they are not really useful where time sensitive measurements are needed.

Price

Most Watermark sensors are inexpensive and are therefore affordable for most operations.

Installation & Maintenance

A watermark sensor needs to be calibrated to the individual field it is installed in. This requires a soil test, to be able to ensure correct calibration of the sensor.

The installation process is straightforward, however the units may need to be removed in case the ground freezes to avoid damage to the unit.

Soil Types

Watermark sensors work well in most soil types, except in soils that contain a lot of clay or are very saline as this impacts the electrical resistance of the sensor.

Measurements

A watermark sensor will only show matric potential. Matric potential is a measure of how hard/easy it is for plant roots to extract water from the soil.

Summary

Cost-Effective: Watermark sensors are relatively inexpensive and affordable for most farmers.

Durability: They are robust and can last several seasons with minimal maintenance.

Ease of Use: These sensors are straightforward to install and use, making them accessible for various users.

Calibration Needs: They require calibration for different soil types to maintain accuracy.

Moderate Accuracy: While they provide useful data, their accuracy is not as high as TDR or TDT sensors, especially in extremely wet or dry conditions. Slow reaction times of the sensors make them unsuitable for operations that need real-time data.

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