>You can't have an excess of food and famine at the same time.

Sure you can. Food supply is not just a question of production, you also need logistics and will to distribute. There is currently a global food surplus, but areas of the world are still undergoing famine.

>in fact food prices were dropping

Up to 1931. If you look at the data into the actual Dust Bowl years, 1932 to 1936, prices go back up significantly.

>It doesn't even make sense, Oklahoma isn't dry, the American south is very humid.

But the Dust Bowl occurred in an extended drought period when Oklahoma was incredibly dry. And while it's true that topsoil was lost from fields that weren't farmed, those fields were fallow because of the drought - crops couldn't be grown in the dry conditions.