Butters

Hi, i am thinking about to code a mod which consists of new seeds, crops and food. I want to implement a system to improve the quality of crops (and their products) by using fertilizers. For example: You place your seed with quality "1". The quality of the growing crop will also be "1" (because the seeds quality is "1"). Now if you use fertilizer at the crop the quality increases by one (so now it is "2") and if you harvest the crop you will get a seed and food with quality "2". I do not want the items to be stackable if they have different qualities and i do not want to add tons of subtypes for every item. So can you give me a hint how i can realize it without using subtypes? I was thinking about to use TileEntities to store the quality into NBTTags but i am not sure about how to split the items automatically. I also thought about Metadata but i am sure it will not be possible with crops.