this is one could be down sized is my guess, similar to the ATV unit,
when the teeth are in the soil and pulling I do not know how much a lawn tractor could pull,
the power rake and a catch (some what like the hay buster, could take less power, say 3 foot wide, and even if the catch was not the rolling cage like the hay buster, but a small lift like thing like the bucket here, my guess is one will have to get some idea of how much your tractor can pull.
one could make it some what like a potato digger, and on smaller units they vibrate the digger part so the tractor does not have as much drag on it, (some think like a vibra plow, they use to trench in water lines and cable)
Potato Digger to Harvest Potatoes