Improving crop yields with fertilizer management

[Tormen]

I've been growing vegetables on my farm for a while now, but I'm noticing yields dropping year after year. Want to turn this around with fertilizer, but I need to know where to apply more and where to use less. Don't want to make things worse by overdoing it or missing the spots that really need it. How do you figure out which parts of the field need more fertilizer and which need less?