I hate to get technical (OK, actually I enjoy it! ) but he's talking about "ground layering". These are usually done with side branches although, like HeadShake said, it should not be any different. Air layering would be to bag up a soil pouch up on the branch. Very interesting topic, mad reps yo.

Layering - Wikipedia, the free encyclopedia

Quote Originally Posted by headshake
it does work and it's called air-layering. it's not different than taking cuttings and putting them in soil.

-shake