"The farmers have to research those machines."
Translation:La farmistoj devas esplori tiujn maŝinojn.
I got the same problem like you. It seems that bieno refers to the land underneath a building (or a field), while farmo means, well, a farm (although it seems that the original definition asks for the land to be rent). I would be in favor of accepting bienisto here, although I’m not sure.