most were planted too late and thick if the goal was big roots so whats left of those is a shriveled inch wide rotting root. but a few areas i planted earlier and bigger spacing i picked some that were easily 2.5" wide over like 16" of the root and were good food. but the remaining ones look like this rust colored bit there
basically a temporary storage tube that grabs the remaining nutrients and lets it rot back out into the soil in spring. thats the over simplified explanation
more proper theory of cover crops and nutrients, talk about phosphorus for example, theres lots of it everywhere compared to what your adding, it just becomes bound up very easy. when you add P fertilizer 80-90% just joins the stockpile of bound up P. the way it gets plant usable is bacteria and fungi ect. and to have those multiply and be happy you need as much variety of plants growing and rotting as you can.
so conventional thinking is kind of backwards. people always look at it as soil makes plants, and nutrients makes plants, but plants are whats required to make the soil good. they feed the biology which aggregates soil to be soft and crumbly, and they feed the biology that makes nutrients not be locked up, or with N they prevent loss or can capture from the air. roots rotting increase organic matter. pretty much everything plants like to have is gotten via plants