Why are the midwestern states some of the world's best for farming? good soil temperate climate long growing season ocean access

Fertility is one thing, productivity another, and best land is still another.

I could for instance say well here's some peat soil in northern Minnesota, highly fertile in many ways though deficient in some ways in others depending on the crop.

Is it the best land? Well, it's really good for growing bluegrass sod. It's not great for grain crops and due to it's location it wouldn't be good at all for lemons.

Much desert land has become extremely productive, and very expensive, but it is no where near the most fertile. What you have though is land that due to it's location, with additional water, can grow a wide variety of crops and many of them very valuable.

Another thing in general, is that organic material levels go up as you go north. So land in general gets more fertile as you go north. But productivity doesn't necessarily follow that same trend because the same shorter season and cooler temps that helped build and maintain that organic material, limits growing seasons and crops growth.

Hope that helps.