What is a soil?
A soil is a living being.
An ideal soil is the balance of clay and organic matter.
The best balance being half clay, a quater of animal organic matter and a quater of vegetal organic matter.
But the dynamic of a soil is brought by the life it can entertain: which is mainly bacteria and fungis.
There are two sorts of bacteria: the aerobians at the surface, the anaerobian deep under.
It is the relationship between both that makes the soil live: they exchange water, minerals and metals. They make the rain penetrate in the soil: they are responsible for bringing water deep under as for bringing water at the surface when needed.
This why when you plough you destroy all this balance and produce methane by destroying the anaerobian bacteria up and the aerobian bacteria under. The other reason for not turning the soil up under is that you ruin all the net created by the fungis and their mycelia. These are responsible for exchanging goodies with the plants and bringing them exactly what they need where they need it right at their roots.