"your harvest": to exclude that which appertains to the Temple and to gentiles — whence they ruled: A gentile who reaped his field and then became a convert is exempt from leket, shikchah, and peah. R. Yehudah makes him liable for shikchah; for shikchah obtains only at the time of sheaving, (at which time he was a Jew.)
R. Yossi Haglili says: (It is written) "When you reap your harvest in your field and you forget a sheaf": Wherever your reaping obtains, shikchah ("forgetting") obtains in the sheaves; wherever your reaping does not obtain, shikchah does not obtain in the sheaves — which is to say that if the Temple reaped (the field) and an Israelite bought it, he is exempt (from shikchah); if a gentile reaped (the field) and an Israelite bought it, he is exempt.