The balance of what is fuel and what is not seems odd occasionally. For instance, farming:weed is considered fuel, but neither farming:hemp_leaf nor farming:seed_hemp are. Both can be turned into farming:hemp_oil at which point they become fuel with burn time of 20. Wouldn't it make sense to have the individual components be fuel of their own already?
farming:seed_wheat is an item that can only be used for growing new wheat. Without additional mods, there are no other uses. How about turning it into fuel as well? Similarly farming:seed_rice. There probably are more.
I suggest registering these items (and maybe more) as a fuel with burntime set to 1.
I recognize that this is not an obvious bug but more an opinion. There are good reasons to not consider those items fuel. The seeds may be considered too small and the leaves may be considered too wet. If you disagree, please close the issue with a comment stating so.