(Mishnah) (R. Eliezer): A field the size of a Beis Rova (just over 104 Amos2) is obligated in Peah.

(R. Yehoshua): The size of two Seah.

(R. Tarfon): Six by six tefachim.

(R. Yehuda ben Beseirah): Large enough to be able to cut two handfuls. The Halacha follows his opinion.

(Gemara) Question: What is R. Eliezer's source?

Answer: The pasuk says here (Vayikra 19:9), "your field'' and it says about Kilayim (mixed plantings) (Vayikra 19:19), "your field''. Just as over there, the size of the separation between two species of produce must be a Beis Rova; so too, a field must be a Beis Rova to obligate it in Peah.

Question: What is R. Yehoshua's source?

Answer: The pasuk says here "your field'' and it says about Shichechah (Devarim 24:19), "and you shall forget sheaves in the field''. Just as over there, the size is two Se'ah (as if the sheaf is two Se'ah, it is not considered Shichechah, as the field must be two Se'ah, not the sheaf); so too here, the minimum size of a field obligated in Peah is two Se'ah.

Question: What is R. Tarfon's source?

Answer: Just as a something is considered a patch when it is the size of six by six Tefachim (in order to be able to plant five different crops without transgressing the prohibition of Kilayim - see Maseches Kilayim 3:1) so for Peah it is considered a field when it is six by six Tefachim.

The Mishnah taught that R. Yehuda ben Beseirah said - Large enough to be able to cut two handfuls. The Halacha follows his opinion.

Question: Is R. Yehuda ben Beseirah referring to the way the harvesters cut, meaning two full handfuls, or even if he grabs two minimal amounts?

Answer: From the pasuk that states (Tehillim 129:7), "[Let them be like the grass]...with which the harvester cannot fill his hand, nor the sheaf-binder his arm'' - this shows that one is only called a harvester when he grabs full hands.