I have tried all kinds of stuff too.. like azomite, seabird guano, dr. earth, seaweed extract / liquid seaweed, worm castings, compost,.. (you can't tell from my soil because I mix it in.. since it's mostly sandy soil, after I mix it in and water a few times, it turns back to grayish white).. Southern Ag Chelated Citrus Nutritional Spray (my tangerine tree didn't produce much last year, but now it's full of blooms, haha, almost used the whole bottle to try to fix it back up), and yes even some chemicals (dynagro 7-9-5, alaska morbloom 0-10-10 , and currently trying that bloom booster that JF always uses , 10-52-10 as a foilar spray)..
the best I found to be a mix of Dr. Earth and seabird guano
this year I'm trying a little different too.. have worm castings and kelp meal ready on hand (once I'm allowed on the hill again, but at least 3 months, so that puts it in June
.. it might be too late this year, but still will do it..
Seabird guano (not from Amazon, but from PlanetNatural) - pellet form and 12-11-2, the best I seen for nitrogen.. about 2-3 cups per plant all around..
http://www.amazon.com/dp/B007QVD5TO/ref=sr_ph_1?ie=UTF8&qid=1458134731&sr=sr-1&keywords=seabird+guano