From the Super Mario Wiki
Golden Turnips are items that appear in Super Mario Odyssey. They are large, gold turnips that can be plucked from the ground and carried. Three of them appear in the Luncheon Kingdom and they will each grant Mario with a Power Moon when thrown into a large bowl of soup located in Peronza Plaza. If Mario throws a Golden Turnip and does not pick it up after a while, it will disappear and return to its original location. They are usually seen alongside normal Turnips.