Sefer HaChinuch ספר החינוך

To separate the poor tithe: To remove the poor tithe in the third and sixth year of the sabbatical cycle. And about this is it stated (Deuteronomy 14:28), “At the end of three years, you shall remove all of the tithe of your produce, etc. and you shall leave it in your gates.” And in that year, they would separate the poor tithe instead of the second tithe of other years, and not separate the second tithe at all.

From the roots of the commandment of this matter is that which I wrote on the commandment of loaning to a poor person in the Order of Mishpatim (Sefer HaChinukh 66).

From the laws of the commandment are that which they, may their memory be blessed, said (Mishneh Torah, Laws of Gifts to the Poor 6:7, 10) that the owner of a field through which poor people passed must give everyone of them tithe enough to satiate him, as it is stated (Deuteronomy 26:12), “and they shall eat in your gates and be satiated.” And how much is enough to satiate him? From wheat, he should [give] no less than half a kav; from barley, no less than a kav; spelt, no less than a kav and a half; fig-cakes no less than the weight of twenty-five sela; wine, no less than half a log; oil, [no less] than a quarter log; a quarter of a kav of rice; a litra weight of vegetables; three kav of carobs; ten nuts; five peaches; two pomegranates; and one etrog (citron). If he had a little [produce] and the poor are many, he places it in front of them and they divide it among themselves. And there is no right for the owners to benefit [by choosing who receives] the favor [for] the second tithe that is divided on the threshing floor. [If] a man and a woman come to take, we give to the woman first and afterwards to the man. [These] and the rest of its details are elucidated in Tractates Peah, Maaserot, Demai and in [various] places in [the Order] Zeraim, and in Makhshirim and Yadayim. And with God’s help, I will write in which place it is practiced and at what time, in the Order of Shoftim (Sefer HaChinukh 507).