Inputs: <BR>Jellynuts <BR>Yumako
Returns: <BR>Jellynut/Yumako Seeds <BR>Jellynuts and Yumako (when plastic backs up)
Outputs: <BR>Plastic 30/sec <BR>Spoilage x2 (rate varies)
Short Version
To start the system, add nutrients to the top four biochambers and provide inputs. Alternatively, add about half a stack of spoilage to each assembler. Production system will slowly turn on as biochambers get nutrients and ingredients.
This blueprint does have circuits. This is to return inputs when plastic backs up (better to use them elsewhere). Other circuits help nutrient production in the event of issues.
Spoilage outputs can be burned or used elsewhere. Seed returns should be sent back to your agricultural towers.
Long Version
There are circuits, but no combinators to keep things simple. (room for minor improvements if you're inclined to add combinators)
Tested in sandbox for a long time on x64 speed. Spoilage is emptied from every building and belt as it occurs. The bioflux to nutrient biochamber empties its spoilage onto the center nutrient belt where it is later filtered. All other places will filter it's spoilage directly into spoilage belts.
It only takes 7 unmodified biochambers to fill a red belt, but I felt trying to balance both lanes on the belt was not worth the effort. If you wish to extend this blueprint to accommodate a higher speed output belt, you will need to upgrade the Yumako input belts as a full yellow belt just enough to meet the production of this system.
The top crop processors will feed the wood boxes above them. They DELIBRATELY spoil. These will feed the assemblers in the event of a nutrient outage. It checks to see if the crop on it's side is there (to ensure replenishment) and if the nutrient belt has zero nutrients. If these two requirements are met it will create nutrients from spoilage to jump start the system.
In the event of an plastic backup (expected if you inevitably use less plastic than you produce), the jellynuts and yumako are released to the return to be place back in whatever your main line is and the input belt halts to prevent more crops from entering (they would just spoil for no reason). This helps keep inputs fresh for when they actually needed and not waste inputs in the system. If you'd rather not use the crop return feature, you can remove those return belts.
Finally, the system will return seeds which is critical to keep producing your two main crops and keep your crop processing biochambers running.
Between the nutrient and crop return circuits, the system can handle most issues and act on its own. It will stop in the event of plastic backups or missing inputs but will restart fine when these problems have been dealt with.
There's a lot going on even without the simple circuits so it's going to be/look complex just for plastic. That's the nature of having to deal with nutrients and spoilage on Gleba.