I would like to see a topic section on fertilization for citrus. Depending where you read, there are a variety of "recommendations" on the frequency and strength of fertilizer for young (up to 3-4 ') trees. Some Citrus Expos are recommending monthly applications. How much? of what? (6-6-6, 8-8-8, 19-10-5 ?). What are the results of too much fetilization?
My specific situation is that I have 21 citrus trees in sandy soil (total sun) on the coastline of SC. The pH of the soil ranges from 6.5 - 7.4. Irrigation is via drip. Three trees have fruited early, grew to small marbles, threw them all off, started over and repeated the cycle. The trees in question are Bearss Lime, Harvey Lemon, & Satsuma Tangerine.
I'm not sure I am dealing with a fertilization problem or not.
Any comments would be appreciated.

How old are your trees? Sometimes it has to do with age.

It may help to boost the fertilizer application with ammonium sulfate just before blooming time and then increase irrigation during the bloom till the fruits are golf-ball sized. I have they same problem as yours and did this to my algerian clementine and satsumas, now I seldom lose a lot of fruits. I still have fruit drops but retain fruits more than normal load that I have to thin them out around the golf-ball sized stage. you will have to correct your problems next year, apply ammonium sulfate fertilizer during late winter to early spring just before the first flush.

For my inground citruses, I never use slow-release fertilizer and stop all fertilizer application by end of July. The main reason is that you don't want to have growth flushes during the warm spells of the fall and winter season, only to be damaged by frosty events. A slow fertilizer release will supply you with fertilizer during to cold months, so that is why I never use them for my inground citruses. For potted, yes, they are almost exclusively fed with slow release fertilizers as I can bring the pots in whenever I can feel the chills in my bones.