I think you might be confusing terms here. “Monoculture” farming doesn’t mean that a farmer doesn’t rotate their crops, it means that, within a field, they only plant one crop in one year. So though 90%+ of US farm production is “monoculture”, a significantly smaller percentage of farmers don’t rotate their crops. Corn-soybean rotations are the norm in US ag production, which actually pair well in terms of soil nutrients (soybeans and other legumes fix nitrogen in the soil, while corn consumes).