Charles Ellicott Commentary Deuteronomy 14:28

"At the end of every three years thou shalt bring forth all the tithe of thine increase in the same year, and shalt lay it up within thy gates:" — Deuteronomy 14:28 (ASV)

At the end of three years you shall bring forth all the tithe. —This is called by the Jews Ma’aser ‘ni, "the poor’s tithe." They regard it as identical with the second tithe, which was ordinarily eaten by the owners at Jerusalem; but in every third and sixth year was bestowed upon the poor.