Specially engineered specifically for harvesting potatoes, these Harvesters come on two basic configurations - towed, and self-propelled.
Depending upon how large your farm is and the number of fields one of the two will be the most appropriate. For small to medium farms the towed harvester will work best, but for large to very large operations the self-propelled harvester is best. The base game comes with the following dedicated Potato Harvesters:
In addition to one of the above Harvesters you will ALSO need to own and operate the following Potato Topper unit - because you cannot harvest potatoes until you have "topped" them - that is to say you must run a Topper over the crop to remove the above-ground parts of the plant and only then run the harvester to pull up and harvest the edible bits, which are below ground (potatoes being a root crop).
Operating the Topper should be easily accomplished using existing tractor units on your farm as you are not likely to own a unit that cannot produce the required 61 hp.