If this device was remotely managed and you had access to the sensors mentioned in the white paper then the tasks above may not be that hard for smaller plots of land.

Teaching it what rain is? How about a query to Yahoo Weather.

Teach it what ripeness is? Imagine this device taking pictures of each plant every day and emailing individual images to you. Start out by manually training on the corpus based on what you think is ripe or not ripe. From their you would have a good stepping stone to start machine learning based on color and size of the plant. Same goes for unidentified plants in the garden that may be weeds.

I think the idea of total automation and remote sensors could make managing a farm a one person job.