Deuteronomy 14:22

Be mindful to tythe your fruitage of whatsoever cometh forth, and which you gather in from the field year by year; not giving the fruit of one year for the fruit of another.

This passage, in turn, is connected to the passage You must set aside the tithe because Scripture has informed us that one may not eat a ritually impure bird, nor a ritually impure beast, nor a beast that has died by itself — thereby concluding the discussion of meat. With respect to grain , on the other hand, there is a consecrated portion which may not be eaten except in the appropriate place.

The Spaniard Rabbi Y ә hudah HaLevy — may he be for us a light from above! — has said that the phrase which the field goes out year after year modifies the word seed (and thus denotes the seed that one takes out into the field). In my opinion, the meaning is more straightforward: it denotes the produce that the field brings forth. If you should object that Scripture uses the term “goes out”, which is an intransitive verb, I shall show you “the city that brought forth [literally: went forth] one thousand, shall have one hundred left” [Amos 5: 3] in which the verb “shall have left [singular]” is definitive proof of the other verb’s transitivity. Our Sages, of blessed memory, have asserted [Sifrey on this verse] that this verse describes the Second Tithe. Understand that if you count upward, you begin with One; if you count downward, you begin with Ten. This is the mystery of the first-born, and of the tithe [cf. comment on Leviticus 27: 32 ff.]. Understand that the number One is in a class by itself. So is the number Ten (which corresponds to the number One), because it is both the beginning of the tens, and the end of the units. All the other unary numbers are contained within them, between one and the other. Because One and Ten are the fundamental quantities, they and the numbers midway between them — i.e., Five and Six — are called “round numbers”. Accordingly, the silent letters in the Hebrew alphabet [’ alef, heh, vav , and yod — Translator] are those that correspond to these four quantities; and among them are the letters that form the Glorious and Awesome Name [cf. comment on Exodus 3: 15].

THOU SHALT SURELY TITHE ALL THE INCREASE OF THY SEED. This also is a [previously stated] commandment that he [Moses] now explains. For He stated, And all the tithe of the Land, whether of the seed of the Land, or of the fruit of the tree, is the Eternal’s; it is holy unto the Eternal, and He further said, And if a man will redeem aught of his tithe, he shall add unto it the fifth part thereof., Verse 30. Now these verses do not refer to the tithe of the Levites [i.e., the First Tithe], for of that it is said, And ye may eat it in every place, and it is unconsecrated food, and what reason is there for its redemption? And now he explained that He obligated [them] to tithe all the increase of thy seed [i.e., to set aside the Second Tithe] in order that he himself and his children eat it before G-d, that thou mayest learn to fear the Eternal. For the priests and judges who stand there before the Eternal, the teachers of the Torah, will instruct him in the fear [of G-d] and teach him the Torah and the Commandments. And he explained [here] the meaning of the redemption He mentioned there:, Verse 30. it is because sometimes the [Second] Tithe will be abundant because the Eternal will have blessed you and the way will be too long for you, and [therefore] it is better to redeem it with money and to bring the redemption-money [to Jerusalem for use in buying food]. He did not mention [here] the fifth [that is added to the value of the Second Tithe when redeeming it] because it has already been mentioned [there in Leviticus]., Verse 30.
The purport of the expression, that which is brought forth in the field is “‘and all’ that which is brought forth in the field,” [so that the phrase does modify ‘the increase of thy seed,’ and adds additional categories of produce to the requirement of the Second Tithe], just as He has said, whether of the seed of the Land, or of the fruit of the tree, and the sense thereof is “that which comes forth ‘from’ the field.” Now the intent of the expression all the increase of thy seed is not that he is to tithe all produce from whatever he seeded, nor everything that is brought forth in the field year by year. The sense of the verse is that one is to tithe, of those species which are liable to the tithe, all of his produce [these being grain, wine, and oil, as will be explained] and all that was brought forth of them in the field. He is warning that …

עשר תעשר, for by tithing the crops of the fields and orchards as well as that of your livestock, you will actually increase their numbers (G’d will see to this) instead of decreasing the amount at your disposal. This is what our sages meant when they said in Shabbat 119 עשר בשביל שתתעשר, “give the tithes so that you will be enriched” (with the dot in the letter ש of the word תתעשר on the right hand side.).

היוצא השדה שנה שנה, “which is brought forth from the field year after year. The apparently superfluous words ”year after year,” are interpreted by Sifri as meaning that tithes must be given from the current harvest year not two tithes from a single harvest. An alternate interpretation: the farmer is assured by the Torah that if he tithes this year’s harvest properly he will be assured of a bountiful harvest in the year following.