FARMBOT is an X/Y -2 axis plotter with a water sprayer head.
you set your plants on the table and then set water times.
the X/Y locations are then watered accordingly.
As for the use of encoders and steppers, they can be used for feed-back but a simple home routine eleminates the need.
for a multiple axis mill that might take hours to complete, they can re-zero on the fly. and if you have ever gotten half way through when the cutter breaks.... you know how hard it it is to pick from some point in the G-Code.
for the OP : there are lots of search results on using encoders. if you cannot find what you need, then please post the make and model of the encoder. there are scores of possible encoders styles, so we would need specifics.