How do farmers work to prevent wind erosion of topsoil?

The best proven method to prevent or minimize soil erosion is adopt no-till practices, or convert the fields to permanent pasture for livestock and rotational-graze them on there. Nature has long known that having plants cover every square inch of exposed soil will naturally reduce or prevent erosion of the soil.

Planting trees will only minimize wind erosion, it won't prevent it; you will still have soil exposed to the elements, and when you get powerful gusty winds that even the trees cannot break you will still get soil blowing away. Same thing with contour plowing--you're still exposing soil to the elements regardless if you're going with the lay of the land. Strong winds can still up and blow some of the topsoil away.