Years ago I experimented with a wheat-corn-beans rotation here on our heavy clay soils.

Long story short, it is very hard to get bean yields up on our clay soils.

The bad thing about  clay is that it holds water in the spring. The good thing about clay is that it holds water through the summer. Also not much tile here.

If you look at the areas with great bean yields, they generally have well drained soils. And regular moisture when needed.

On the other hand we can grow great corn on these rolling clay hills. The clay tends to hold water.

Soil type appears to me to frequently be the limiting factor on bean yields. You can see that on your yield maps.