The following items are buried, because they are, for one reason or another, forbidden for benefit: the aborted fetus of a sacrifice or its afterbirth – because one cannot use them; an ox that killed a human and was executed by stoning – because its meat is prohibited for benefit; the shorn hair of a nazirite, and meat cooked with milk – because these, too, are forbidden for benefit.
And the following are burned: chametz on Passover – since Rabbi Yehudah says that it is the proper way to destroy it; Kohen's portion of grain that became ritually impure – because it would be too easy to make a mistake and use it; and fruit of a tree for the first three years (orlah), as well as grain that grew in a vineyard – for the same reason of preventing a mistake.
All things that must be buried may not be burned, and vice versa. Why is that? Because in the case of things that must be buried, their ash is also forbidden for benefit, but for things that must be burned – their ash is permitted.
End of Tractate Temurah
Art: David Fulton - A girl in an orchard with a basket of apples