Menahot 84: The First Fruits of the 7 Species

Which barley is to be used for the omer offering? During a sabbatical/shemitah year, they couldn't plant, but they could collect the natural growth, which they did. That collection needed to be as for food, however, and not for fuel -- because shemitah produce could not be burned. But it wasn't quite burned either.... Also, a deep dive into "first fruits/bikkurim," and how they were to be brought from the 7 species from the land of Israel. Plus, refinement of the details of the bikkurim as brought, based on the verses, and also the basic growth and whether it was in a field or elsewhere, for example. But why weren't bikkurim offered for all fruits and not just the 7 species?