fruit won't set on dwarf washington navel

[bea]

I have a dwarf washington navel planted 6 yrs. ago in a large cement planter.Every year fruit gets as big as a quarter turns yellow and falls off. Gets full sun, citrus food as recommended,water when needed.I live in So. California.Any suggestions for problem?

 

[LightningLoader]

Something's stressing your tree, but I can't tell what since it sounds like you're doing everything else right. My husband was a citrus major in college and he says you're S.O.L., and that the tree is only supposed to lose 2% of the fruit, not 100%. This doesn't mean that your problem can't be fixed, just that it is an unheard of problem around here. Maybe it has something to do with it being potted?