3,130. Why Peah is Left at the End of a Field

Hilchos Matnos Aniyim 2:11

If the owner of a field harvested his entire crop without leaving peah, he must give some of the stalks he harvested as peah; he need not tithe what he gives as peah. This is so even if he gives the greater part of his harvest as peah. Similarly, if he threshed his grain but has not yet winnowed it, he must give peah before he takes tithes. However, if he threshed and winnowed his grain with a shovel and a pitchfork, completing its work, he must tithe it and then give the needy tithed produce equal in volume to the peah for that field. The same is true when it comes to trees.

Hilchos Matnos Aniyim 2: 12

Peah is only left at the end of the field. This is (a) so the needy will know where to go for it, (b) so passersby will see it and not suspect the owner of violating the Torah, and (c) to keep dishonest people from harvesting the whole field and telling observers that they left peah at the start of the field. This also keeps the owner from waiting until no one’s around so that he can earmark the peah for a needy friend. If a person violated this law and left peah at the start or in the middle of his field, it counts as peah but he must also leave the proper volume of peah for the part of the field that remained after he left that peah.