Mishnà su Levitico 25:6

Beth Shammai says: [produce pronounced] ownerless with respect to the poor [only] is counted as ownerless. But Beth Hillel says: it is not counted as ownerless unless it is made ownerless also with respect to the rich, as in the year of release (shmittah). If all the sheaves of the field were of one kav each and one was of four kavs, and it was forgotten, Beth Shammai says: it does not count as forgotten, And Beth Hillel says: it counts as forgotten.

They said an important general principle with regard to the sabbatical year: Anything that is usually designated as food for humans, one may not make a poultice of it for a person. And there is no need to say [that he may not make a poultice of it] for a beast. Anything that is not usually designated as for food for humans may be used as a poultice for a person, but not for cattle. And anything not usually designated either for humans or for animals, but now he thought to use it as food for either a person or an animal, we impose upon it the stringent laws applying both to people and beasts. If he thought to use it as wood [for a fire], behold it is treated as wood [and the laws of sheviit do not apply]; for example, savory, hyssop, or thyme.