I am still pondering this hard Rambam 2:11 in Peah. The owner of the field harvests the whole. He was supposed to leave 1/60 of the standing wheat to the poor. He gives from what was reaped to the poor. And if he gives most of what was reaped, that is not obligated in truma and maasar. [Truma is what is given t priests. Maasar is what is given to Levites. Clearly neither applies to peah which is the edge of the field which is given to the poor.] Only if he finished all the work [reaped and threshed], then he has to take truma and maasar and give to the poor.
Again what is this "most of what was reaped"? Normally one can give his whole field as peah except for the first stalk. [Obviously of he does nothing with the field at all then it can not be "peah" i.e. the corner. There has to be some beginning work in order for the rest to be what was left
So Rav Shach brings from the Yerushalmi perek 2 halacha 5 in Peah that if he even started to reap the 1/60, then the obligation of peah goes on the sheaves, not the standing wheat any more.
That helps a little. So now he can give the whole 59/60 as peah. But still I am wondering about the Yerushalmi itself. Why can he not just give what is left of the standing ears as peah and what in them does not make up the whole 1/60, to give the needed amount from what was reaped?
