Aside from the zero’ah (shoulder), lehayayim (cheeks) and kevah (stomach) that butchers are obligated to give to the kohanim (see yesterday’s daf, or page), under ordinary circumstances, a farmer will separate:
1. Terumah Gedolah – a small portion of his harvest that is given to a kohen. This produce is sanctified and can only be eaten by kohanim when in a state of ritual purity.
2. Ma’aser Rishon – one-tenth of the remaining produce, which is given to a levi. This produce does not become sanctified, and the levi can do with it as he pleases.
3a. Ma’aser Sheni – one-tenth of the remaining produce, which is taken to Jerusalem and consumed there. This tithe is given during the years 1, 2, 4 and 5 of a seven year cycle.
3b. Ma’aser Ani – in years that Ma’aser Sheni is not given (years 3 and 6), one-tenth of the produce is given to the poor.
The Gemara on today’s daf notes, however, that according to Rabbi Elazar ben Azariah Ma’aser Rishon was not to be given to a levi, rather it was also given to a kohen. The Gemara explains that this ruling was instituted by Ezra haSofer as a punishment to the levi’im who did not join him in returning to Israel at the beginning of the Second Temple period.
In Masechet Yevamot (daf 86a) there is a disagreement regarding the obligation of Ma’aser Rishon on a biblical level. According to Rabbi Akiva, Ma’aser Rishon must be given to the levi’im based on the clear statement in Sefer Bamidbar (18:26). Rabbi Elazar ben Azariah ruled that it could be given to kohanim as well, since we find kohanim are called levi’im in many places in the Torah. The Gemara there also explains that there is a disagreement about Ezra’s injunction – whether aside from being given to kohanim, it was also distributed to the poor.