Demai, Chapter Six, Mishnah Two
In the second section of the previous mishnah we learned that one who rents a field from another Jew and in return pays the field owner a set amount of crops must give terumah but not tithes. Now we learn about a Jew who rents a field under a similar type of arrangement, but this time, from a Gentile.
1) One who has hired a field from a Gentile [for a fixed amount from the produce], he first gives tithes [from the rental] and then gives it to him (the field owner).
2) Rabbi Judah says: even if one rented from a Gentile a field which had formerly belonged to his fathers [for a share in the produce], he first gives tithes and then gives it to him.
Section one: In this case he must separate terumah and tithes because he knows that the Gentile will not separate the tithes himself. According to one explanation of this mishnah, the implication is that even though the land is owned by a Gentile, the produce still must be tithed since it is grown in the land of Israel. Since he knows that the Gentile wont tithe, he must tithe it himself. In contrast, when the field belonged to a Jew, there was a chance that the Jew would tithe the produce himself and therefore the rabbis were lenient upon the renter.
Section two: Rabbi Judah emphasizes that even if the field once belonged to a Jew but had been sold to a Gentile, he still must first separate tithes and then pay his debt from the produce. Most commentators explain that according to Rabbi Judah, the rabbis forced him to separate tithes so that he would try to buy the field outright from the Gentile, and thereby restore land in Israel to Jewish hands.