Mishnayos Maasros Perek 5 Mishnah 5

הלוקח שדה ירק – from the heathen.

בסוריא – they are the lands that [King] David conquered, such as Damascus, Aram Naharayim and Aram Zovah. But in some of the things, he made them like the Land of Israel, and in some of them, not.

אם עד שלא בא לעונת המעשרות חייב – since for at the time that they come towards the liability [for tithing], they are in the possession of an Israelite. But if if the time of the liability [for tithing arrived when it was in the possession of an idolater, he is exempt [from tithing].And regarding this thing, they made Syria like the conquest of an individual, which is not called a conquest.

ולוקט כדרכו – and he is exempt from tithing even what was added in his possession. But he should not hire workers, for we are concerned that perhaps they will come to work this, even in a field that he purchased even before the time arrived for tithing. But Rabbi Yehuda did not make [this] decree.

פטור – even though he doesn’t have in the body of the land anything.

רבי יהודה אומר אף לפי חשבון – He is referring to the matter of the first Tanna/teacher. But this is what he said: that just as he is liable [for tithing] if he purchased prior to the arrival of the time for tithing, to tithe on everything, that is so, that he is liable [for tithing] if the season for tithing has arrived, to tithe according to the percentage that was added to his possession, such as for example, if they brought one-third in the hand of the heathen, he is liable to tithe on the two-thirds that were added to his possession. But the Halakha is according to Rabban Shimon ben Gamaliel.