C. F. Keil and Franz Delitzsch on Leviticus 27:30-31

Lev 27:30-31

Lastly, the tenth of the land, both of the seed of the land - i.e., not of what was sown, but of what was yielded, the produce of the seed (Deu 14:22), the harvest reaped, or “corn of the threshing-floor,” Num 18:27 - and also of the fruit of the tree, i.e., “the fulness of the press” (Num 18:27), the wine and oil (Deu 14:23), belonged to the Lord, were holy to Him, and could not be dedicated to Him by a vow. At the same time they could be redeemed by the addition of a fifth beyond the actual amount.