ground moisture sensor

Hello guys! I hope someone of you will help me
when im calculating the moisture of the ground (pretty dry one) the sensor tell the serial monitor a number between 300-368 and when I put it in the air it says number between 140-168 and when i soak it in water it says a number between 93-108 please help me to neutralize the interruptions in the system
thank you!

There in something not working.:
Link to sensor ?
Connections ?