Applebuck

Most people don't realize it, but Earth Ponies definitely have their own complex magic system similar to Unicorns and Pegasi.  I imagine that the art of applebucking is part of a larger set of (originally) combat-oriented earth magic that uses subtle manipulation of the ground to provide extra leverage, force, and precision.  Earthpony magic isn't usually as visible as it is in this piece, and I like to imagine that it is that way because it takes an exceptionally powerful earth mage to create visible spell effects.  (Applejack would obviously be one of these, regardless of whether or not she realizes it.)