Yes. The turnip or radish will take up available N and store it in the bulb.
The best thing is to just leave them alone.
Left alone, the bulbs rot and decompose over winter and by the time that process is complete....its time for spring planting.
You can graze the turnips. The cows or whatever will eat the bulbs and leave only a husk in the soil.
The nutrients in that bulb will be converted into cow schit. If you have an operation like mine....cow schit is not safe. The dung beetles will convert the dung into a too volatile source of N.
However....turnips grazed in late fall/winter will be converted into dung and no or very few dung beetles will be on the job at that time.
Bulb crops are the original Time Release Nitrogen.
