Fertilizing fruit trees: sorting out conflicting advice
I'm looking for some perspective on how to fertilize temperate-climate fruit trees (apples, pears, plums, etc).
I'm in the Sacramento Valley, and my usual reference for garden matters is the ag extension web site from the University of California at Davis. The page I found there told me to use either compost or a pure nitrogen fertilizer such as urea, and gave quantity guidelines.
When I mentioned this to my wife, she said flatly that I got it wrong. She pointed out that the special fruit tree fertilizer we used last year was 12-4-8, and said that a nitrogen-only fertilizer would produce lots of leaves but no fruit.
I went back to the web site to see how I had misunderstood it. I hadn't. Then I looked at some other sites and got recommendations that were all over the map. The University of Colorado agreed that I should use nitrogen only. Another ag extension recommended 10-10-10. Another site (not one I'd consider very reliable) said 0-6-8.
I could explain moderately different recommendations by differences in local climate and prevailing soil conditions, but I can't stretch that to cover urea fertilizer and 10-10-10, much less 0-6-8.
Can anyone clarify what I should use on our fruit trees, and why I'm finding such wildly different recommendations?