I think all these root crops need a light soil. I have heavy clay soil and
wouldn't bother trying to grow carrots or parsnips without creating a
special area of lighter soil for them to grow in. That or make special
tapered holes for them to be planted in, filled with sandy compost or
what-have-you.

I'm on pretty heavy clay/soil and while I can "improve" a bed each year
for successfully growing parsnips, carrots completely defeat me. Parsnips
are relatively easy.