Related על בבא בתרא 101:19

Rabbi Eliezer says: a piece of ground [large enough to plant] one fourth of a kav is liable for peah. Rabbi Joshua says: it must [be large enough] to grow two seahs. Rabbi Tarfon says: it must be six by six handbreadths. R. Judah ben Batera says: [it must be large enough] for a sickle to cut at least two handfuls and the halakhah is according to his words. Rabbi Akiva says: any size of land is liable for peah and for first-fruits, and [is sufficient] for the writing of the prozbul, and also to acquire through it movable property by money, by deed, or by a claim based on undisturbed possession.