we have logblock. tells us who placed and destroyed things. x__poison__x showed me this farm and explained someone griefed it. So i rolled you back and found over 500blocks worth of crop missing, most of the crops and sugarcane came back when i did so. you can check the pictures below if you want.
(http://i.imgur.com/dzpQHPn.png)
(http://i.imgur.com/b3AFTMw.png)
(http://i.imgur.com/tbTw0Mk.png)