I have finally finished configuring my soil moiture sensor and worked out the kinks with power consumption.
It currently works by using a 2N2222 transistor to turn on the sensor for a few moments to get a measurement and then turning it off again to conserve battery.
I wrote a quick #ifdef to allow me to configure the sensor by placing it in water saturated soil or leaving it in the air.
It uses OBP activation on LoRaWAN and transmits every 15 minutes. I had to modify the LMIC library to support the 915Mhz Australian frequencies.