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.
