Don't waste your time or money getting the fertilizer cert because unless you have the full blown Commercial L&O it is no good. You can't even apply Weed & Feed with that license. Instead, Net work with a smaller CPO operation to do all your application.
Yes at present time Each county has it's own Fert laws and License. However that state also has input to those local laws & licenses.
You can lead a Donkey to water but you can't make the Jackass Drink
"As Americans you have the right to be stupid." John Kerry
"Life is tough, but it's tougher when you're stupid.” John Wayne.