What about with charred agriculture?The problem is the network of Great Plain's grass roots. Grown up over thousands of years, the deeply interwoven system could reach down over ten feet, and was fiercely resistant to conventional tools. Unless you have steel-plows, you'll have a hard time farming there.
I remember reading about it in 1491, how only the top layers were burnt and quickly put out. It seems like that would provide a good base on such a soil with a lot of organic matter?