Hi,
I think my first attempt did not go through.
Instead of using 3.6V or 5.0V I am using a voltage in between. I have taken readings in the same soil with 3.5V and 4.6V (Battery package which, as time goes by, looses power). Kan I take a reading with power in between to be found by interpolation?
best regards
torben
Here in this product description, Grove - Capacitive Moisture Sensor (Corrosion-Resistant) - Seeed Wiki
It is written that the the supply voltage must be 5V or 3.3V. That means, either you have to connect 3.3V pin or 5V pin of the Arduino UNO with the VCC pin of this sensor. No other value should be applied.
Btw, in case you need a proteus library for soil moisture sensor, you can see here: Soil Moisture Sensor Library for Proteus V2.0 - The Engineering Projects
You can download the library and edit that according to the pinout of your sensor if you need to.