Update: This is more about America’s heritage landscapes - grasslands - and less about particular crops. Grasslands provide important habitat for countless species. President Theodore Roosevelt protected millions of acres of grasslands by including them in several National Parks. Converting them to crops destroys habitat for animals, changes and poisons the soil, pollutes rivers, devalues people’s properties, among numerous other environmental harms. Destroying nature for a quick buck is not the right direction for America’s future. The situation is worse when climate change is factored in.
And, the US Forest Service has an excellent overview of how grasslands are threatened by agriculture and climate change.