The only types of soil sensors supported are ones that are dry contact type — they are basically like rain sensors, when the moisture level exceeds some threshold it outputs high (or the contact switch closes) and otherwise it outputs low (or contact switch opens). If you have an analog sensor you can use a LM393 analog comparator module like this:
https://www.amazon.com/HiLetgo-Moisture-Automatic-Watering-Arduino
which takes in analog signal and compares it with an adjustment threshold and outputs a digital signal.