(Baraisa from R. Shimon): For 5 reasons a person should only give Peah at the end of the harvest - 1] theft from the poor - so that the owner should not find a quiet time and then tell his poor relative to take Peah; 2] wasting the time of the poor - so that the poor will not sit and wait all day expecting the owner to give at any time.

3] Because of the tricksters who claim they have already given Peah and they then proceed to select the high quality produce for themselves and give the poor quality to the poor.

4] Suspicion - that passers by should not think that the owner did not give Peah to the poor.

5] The Torah says (Vayikra 19:9), "you shall not fully reap the corner of your field".

(Mishnah): If a gentile harvested his field and then converted, his crops are exempt from Leket, Shichechah and Peah.

R. Yehuda obligates it in Shichechah, since its obligation comes at the time of tying the sheaves.

(Gemara) Question: R. Yehuda seems correct, so what are Rabbanan's reasoning?

Answer (R. Ami citing R. Chizkiyah/ Rav Yehuda citing Shmuel): The pasuk states (Devarim 24:19), "and you shall forget sheaves in the field and you shall forget standing ears" - anything that has forgetting standing ears has forgetting sheaves in the field; anything that does not, does not.

A Jew and a gentile that were partners in standing ears - the Jew's portion is obligated and the gentile's portion is exempt. R. Chizkiyah said in the name of Rav Yirmiyah that there is a dispute (between Rebbi and R. Shimon ben Gamliel as to whether the Jew's portion is obligated).