Charles Ellicott Commentary Deuteronomy 14:22

"Thou shalt surely tithe all the increase of thy seed, that which cometh forth from the field year by year." — Deuteronomy 14:22 (ASV)

You shall truly tithe. —The Talmud and Jewish interpreters are generally agreed that the tithe mentioned in this passage (both here and in Deuteronomy 14:28), as well as the tithe described in Deuteronomy 26:12-15, are all one thing: “the second tithe.” This second tithe is entirely distinct from the ordinary tithe assigned to the Levites for their subsistence in Numbers 18:21, and by them tithed again for the priests (Numbers 18:26).

The tithe described in Numbers was called “the first tithe,” and was not considered sacred. The second tithe, on the contrary, was always regarded as a holy thing.