Here's an Italian study that says organics stores nutrition in soil better for citrus...
[url]https://orgprints.org/7814/[/url] Love the spelling in the abstract...
This Chinese study shows that pushing chemical fertilizer increases the need for trace minerals...
[url]https://www.ipni.net/ppiweb/sechina.nsf/$webindex/38D48BDB7103705C48256B6A0007A971?opendocument&navigator=fruits[/url]
So where do trace elements come from in an organic or wild system? They are etched out of the soils by a weak acid reaction caused by biology, some of which can help the plant greatly. Here's something from the best guy in the biz, Dr. Mike Amaranthus, on why he thinks they're important (I have seen his company on
Modern Marvels, the cable TV show and have had the pleasure of conversing with the good doctor on two ocassions. Smart fellah.)
[url]https://www.mycorrhizae.com/index.php?cid=391[/url]
The Homeowner button will take you to where you can find Dr. Mike's stuff for home use; this is the good stuff...
So the tree is getting the N-P-K from the fertlilizer but it's killed all the biology...but with that biology we need very small quantities of fertilizer, the kind we can get organically, because the plant is ten times better at finding nutrients (because of the symbiotic fungii that are helping feed the plant, because the plant is feeding them). Plus we start a whole host of other trophic cyles as bacteria get eaten by protozoa get eaten by soil mites get eaten by worms get eaten by birds and moles, all releasing nitrogen in the form of, well poop. But that's how Nature works; when we interrupt that cycle with chemical fertilizers, we rob the plant of it's natural systems and replace them with our own. Except we often aren't very aware of what the plant wants, well, because it's a plant and they haven't learned communications yet. Give them time. A lot of time...
So while we aren't 100% certain it's a micronutrient deficiency we do have two scientific papers that suggest strongly that might be the case, and a strong suggestion that the best thing you could do to get better all around conditions for your tree would be to add soil biology and not kill it. Thought about going organic? It won't solve everything, but it does take care of a lot of issues, like infertile soil (and an increasing lack of pollinators; another possible issue...)
HG