I interplanet sunflowers with cucuberits. They do have huge root balls that don’t break down even after a long, cold winter. So, I either remove them to direct seed or leave them in if I am transplanting widely spaced plants. The soil around them is beautiful the next year and filled with worms. I also plant them as a mineral accumulator, but do not have soil test data to back that up.
I love sunflowers as a cover crop, for insect forage, soil building, and aesthetics. Yes, they have a lot of roots - but the roots are arguably the most valuable part of a cover crop! The key is to fit the sunflowers into the right slot in the rotation. Clearly, immediately preceding a small-seeded crop that needs a decent seedbed is not the right slot. We tend to use sunflowers as part of a year- long cover crop that includes annual ryegrass and several kinds of clover. The sunflowers die in the fall and by the time we need the bed next spring the roots aren't much of an issue.
Awesome thanks, y'all!