Hi. I just found out from Sean that this group still exists. I have
been interested in botany for years. I enjoyed the question. Israel
has probably done the most research on xericulture. They were the
inventors of drip irrigation.
The drawback I see with planting your tree in a hole is that the wind,
and possibly occasional rains, could fill up your hole before the tree
grows surface roots to match. It would only work in a very stable,
relatively windless, climate.
Iris, ak elsewhere as bonsaisr.