Open Irrigation is a Raspberry Pi based system that uses weather data from Wunderground. It doesn’t require any additional sensors and can control 4 zones of irrigation per Pi.
Jantinus Daling told us…
The biggest advantage of this project is that it calculates irrigation requirements based on daily average temperatures and plant growth curve. Plant growth data has been obtained from agricultural researches and the included database supports 35 of the most common plant varieties.
While the system is being used for garden irrigation currently, Jantinus hopes to develop it further to for agricultural use.
You can build your own irrigation hardware for the system from these PARTS for around €100. Check out the link below for more information or to help with the open source project.