Looking at that picture; it's circular appearance; it just might be the old cistern of the homeplace. There's not that much growth in that area to stop a farmer from knocking it down and plowing there, BUT an underground cistern built with concrete or brick; just under the soil, WOULD. If it is, expect a lot of trash (today's treasure?), dirt and snakes. Be careful, it could fall in with you.
That jar you found with the dirt in it MIGHT be the sign left by an old-time treasure hunter to let those coming after him know that the treasure has been found. (per KVM's writings). Keep looking thought, there could be others around.