1) LoRaWan is a long range, low power network, an open source implementation of this http://thethingsnetwork.org/ <br/>
2) Using this technology solar soil moisture sensors could report the state over long distances
3) Code is already written for Arduino, So just needs hacking for LoRa wan https://github.com/liseman/growerbot
4) There is a variety of hardware that could be used for this: http://forum.thethingsnetwork.org/t/smallest-expected-node/568
The nodes could do all sorts of data reporting; water levels, item tracking etc
