Edison does not have an RS485 interface, so at least of communication is not available to be used with this sensor. However, I2C and analog are indeed available. If you would like to use several slaves I'd suggest you to read Multiple I2C slaves on Intel Edison I2C-6 Bus. If you would like a digital connection it would be your best option.
In case you would like to use a different approach using mraa, you could use the Grove Moisture Sensor. It has a UPM library available with a tested example, which you can find in upm/grovemoisture.cxx. Just in case you would like to consider another option.