When you jump on wheat crops usually the farmland become dirt, then seeds and wheat be dropped. However if you jump on potatoes and carrots crops farmland become dirt, but crops stay there.

When you jump on wheat crops usually the farmland become dirt, then seeds and wheat be dropped. However if you jump on potatoes and carrots crops farmland become dirt, but crops stay there.

There's a video where you can show it:
http://www.youtube.com/watch?v=rNuBbioQ5LI