See ARRL Antenna Compendium Vol 5

W7JGM, tells of his experiences using a buried long wire antenna. He
compared it to high inverted V and he reported that most of the time
the signal strength was close to the same. He did report that when the
ground got wet his signal dropped.

Regardless

After reading KM5KG's web page describing buried dipole dummy loads, i
will keep my coax and copper in the air! But hey Diamond and Comet sell
vertical antennas with resistors in them and users report good results.
Performance is indeed in the mind of the user.

Pat