This Soil moisture sensor intends to be a lora node as in the greenhourse lora networks. It detect/report the soil status, and the temperature, to the lora gateway, which is accessable with WIFI, so the remote monitor can get all the points moisture status, and then control the pumps for irrigation。
The voltage of V5 in the high logic might be smaller than VDD if drive the Q1 directly, and it would cause the VCC to never be cut off.