Eladamri's Vineyard

• WWizards of the Coast2004-10-04
  Official Ruling
  Only the first main phase each turn is considered a precombat main phase, even if other combat phases are created (with Relentless Assault, for example).
• WWizards of the Coast2004-10-04
  Official Ruling
  It will not trigger a second time in a turn, even if you cast a spell that gives you a third main phase.
• WWizards of the Coast2007-05-01
  Official Ruling
  This ability is not optional.

Rulings via Scryfall