Carrots and comfey

Got loads of comfey can I put it on next year's carrot bed? Should when growing root veg not use any fertilizer? Or is just horse manure. Last year's bed was greater than 7.5 pH based on test (not sure about the quality of the chemicals) a bit hairy but not over the top. The early Nantes were very good.
Thanks in advance for all your advice/knowledge

It's the lumps in the manure (also stones in the soil) that cause the roots to divide, fertilisers or sieved compost/manure are fine it seems.

I was thinking more about the "hairy bit". And is the problem more to do with how fertile the ground is? Not just to do with horse poo.