Introduction
Soil moisture devices that can act as stationary Internet of Things (IoT) devices.
Article: How IoT Soil Condition Monitoring Is Empowering Farmers
Many companies offer Soil monitoring with IoT, among them mtg.
To look for devices I used the sigfox partner network with a search set to soil.
Simpler devices for Arduino include probes that are based on resistivity or capacitans. The former eventually erode, regardless of the metal used, the latter are more durable. The youtube presentation by Andreas Spiess: Why most Arduino Soil Moisture Sensors suck (incl. solution), summarizes the alternatives.
Youtube
Youtube overview of Arduino soil moisture sensors.
Youtube LoRa
LoRa
LoRa (Long Range) is a low-power wide-area network (LPWAN) technology. It is based on spread spectrum modulation techniques. LoRa enables long-range transmissions (more than 10 km in rural areas) with low power consumption. LoRa devices have geolocation capabilities used for triangulating positions of devices via timestamps from gateways. LoRa and LoRaWAN permit long-range connectivity for Internet of Things (IoT) devices in different types of industries.
This LHT65 LoRaWAN SHT20 Temperature and Humidity Sensor is available at elfa.se.
LoRa + Arduino project for soil moisture
HD Denmark
EVVOS
Wired article
A Solar-Powered Soil Sensor for Serious Gardeners
Enviro Pro
Enviro Pro is an Australian company.
Arduino based stand alone thing
LHT65 LoRaWAN Temperature & Humidity Sensor Built-in SHT20 - 868MHz
Arduino capacitive moisture sensor
You get a capacitive moisture sensor from Banggod for around 3 USD. In Sweden you can get it for 6 USD through fyndiq.se.
Under 1 USD at Ali Express