1. rain sensor is already supported.
2. land sensor: i’ve never seen a land sensor, but it’s certainly possible to add support for it. first you need to figure out if the land sensor is a digital (i.e. on or off) or analog sensor (i.e. continuous level of voltage output). if digital, it works just like a rain sensor, and you can use any of the spare GPIO pins to interface with the sensor. if analog, you can use one of the analog (ADC) pins on OSPi to talk to the sensor. The hardware connection should be pretty easy once you decide which pin you want to use. then you also need to modify the source code to add support. if it’s a digital sensor, you can pretty much copy what’s already there for the rain sensor.