i.e. Of the corn in the threshing-floor, as Deuteronomy 16:13, when you have gathered in your corn. So shall ye heave it, i.e. you shall offer this in the same proportion, to the same persons, i.e. the priests, and with the same rites.
Related Commentaries of Numbers 15:20
Numbers 15:20
20 Ye shall offer up a cake of the first of your dough for an heave offering: as ye do the heave offering of the threshingfloor, so shall ye heave it.