A patented device known in parts of the Discworld which eliminates much of the work and worry formerly associated with planting different crops in a field from year to year or sometimes leaving it fallow. King Verence has one in Lancre as part of his program to modernise agriculture and improve production. It's a horse-drawn implement that resembles "a cartful of windmills", made in Ankh-Morpork1. There has been no report of how (or if) it works.
1 But for its substantial nature and apparent cost of production, one might suspect the involvement of CMOT Dibbler. It may rather be a product of technomancy.