Reading properly, it is not "Blade: Earth," but "Blade of Earth" or "Earthen Blade." Each Weaponskill series, Blade: and Tachi:, label the parent family of the abilities. I.E. each weaponskill of Blade: <"> is what kind of blade (weapon) you are using.
I think its funny this weaponskill's element is not Scisson based(earth) lol