Mix a fertilizer to needed formula by your own will much reduce an agriculture cost.
You may already have some fertilizers and want to try to mix to be an other formula this app will help you by add those existing fertilizer data to the app then try to change each fertilizer quantity, new mixed formula will show you immediately

And you can let this app find a mix proportion of each fertilizers to get desired formula (auto mode) (but fertilizers in the list must be suitable to mix)

App will have some fertilizer data to create a fertilizer list (be aware fertilizer data may different what you have)