It is funny how different farming areas are so different. You and also western Kansas worry about subsoil moisture because that is where a lot of your moisture comes from to grow a crop. I am in a much higher total rainfall area but have a clay pan soil with only about 6-12" of topsoil average (deeper around the creeks, shallower on some hills). We have a clay pan subsoil. We can hold about ten days of growing moisture in the topsoil then we are dependent on rainfall. Too much rain at the wrong time of year is about as often a problem as getting too dry during the growing season because of lack of rain. We sometimes get both in the same year. Often times actually, why our farmland does not bring the sky high prices of other areas.

We don't worry about subsoil moisture that much because of the extremely low transfer rate of water between the top soil and the dense clay pan subsoil.