Have you ever taken a shovel and dug a small pit in your field to look at the profile?? That alone can tell you a lot. I got to pondering one day on how deep I could go before reaching a clay layer.....At 52" I finally hit what was a reddish layer of dirt that still wasn't clay but a definite change in subsoil. I did a test on my topsoil layer that went down 7-8+ inches as well at the next layer that extended from 8"-52"......I wish I would have done a 3rd test on the reddish dirt that extended past 52" just to see.....

I found that the subsoil layer from 8-52" was extremely harsh with a pH of 5.0 while my topsoil layer....that dark layer you see in my profile pics....is balanced at 6.8......That subsoil layer contains no Calcium nor does it have the holding capacity to do so. If I destroy my topsoil that I've built then I have nothing left to plot in but that harsh subsoil. The only way I can improve the holding capacity of that layer from 8-52 inches is with plant roots. No subsoiler goes that deep. Plant roots penetrate into that layer and leave behind the OM of their root systems when they decay....leaving streaks of OM into the subsoil.....these streaks are able to hold CA and improve the micro-area around its root tunnel in that deep layer. Some of the best plants for penetrating roots deep into this harsh environment are "weeds".