How to measure leaf wetness in combination with relative air humidity

How to measure leaf wetness in combination with relative air humidity
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With today's sensor technology, measuring several parameters in real-time is no longer a complex endeavor. In this blog post you can read what a leaf wetness sensor and a humidity sensor are. We go over the advantages of combining these sensors and look at how you can quickly start measuring yourself.

What is a leaf wet sensor?

A leaf wetness sensor detects the presence of surface moisture or dew on the leaf of a plant. Most leaf wetness sensors measure between 0 (dry) and 15 (saturated). A leaf wetness sensor is often used to measure how long the surface of a leaf remains moist. The graph below shows an example of the data from a leaf wetness sensor over a period of ten days.

leaf wetness graph

The leaf wetness sensor can be used to monitor fungal and disease control in the agricultural sector. The sensor can also be used to monitor the operation of an irrigation system.

What is a humidity sensor?

A humidity sensor measures the relative humidity and the temperature of the air.

Relative humidity is a ratio that indicates how much water vapor the air contains compared to the maximum amount of water vapor the air can contain at that moment. Here 100% means that the air is saturated and cannot absorb any more water.

With a humidity sensor that measures temperature as well, you have the option to determine the wet bulb and dry bulb temperature (or air temperature). You can also calculate the dew point on the basis of this value.

For more information about the dew point and how it is calculated, please refer to the following article: How to measure Dew Point and Wet Bulb temperature?

Why combine leaf wetness and humidity?

Dew forms when water vapor condenses on a surface. This phenomenon occurs when the surface temperature falls below the dew point temperature of the surrounding air.

The combination of the leaf wet sensor with the humidity sensor makes it possible to predict condensation on the leaf surface and to measure its duration. This information can be used as input for disease prediction (source: Bouma & al., 2008).

The graph below shows an example of how air temperature, wet bulb and leaf moisture relate to each other. We clearly see that leaves remain wet, especially at night until morning, and that higher temperatures lead to lower leaf wetness measurements.

leaf wetness temperature

How to get started

The fastest and most technically simple way to measure the humidity of a leaf is by visual observation. This is not an ideal way as it is a time consuming task. Moreover, it is not easy to objectively and consistently determine how wet a leaf is.

An easier way to start measuring is with sensors. In this example, we are using our wireless sensor device called Reporter. This device is compatible with renowned sensors such as the leaf wetness sensor from Spectrum Technologies and the humidity sensor with the SHT35 chip from Sensirion AG.

leaf wetness and humidity sensor

In addition to dew, there are other causes of moist on leaves, such as rain or an irrigation system. Crodeon is committed to this by offering a weather sensor and wireless irrigation control.

Measurement data is sent via a GSM connection to the cloud. The customer has access to his data via the Crodeon Dashboard or the Rest API.

Conclusion

We can decide that it is best to combine the measurement of dew or leaf wetness with relative humidity. These measurements are particularly relevant for disease prediction or for finetuning an irrigation system.

Concerning the technology, we recommend not reinventing the wheel. Use hardware and software available on the market today. Start your own measurement project and let us know how it goes!

Sources

*Bouma & al. (2008). “Moisture in the air is crucial for absorption resources” (https://edepot.wur.nl/188)

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