Lemon, well, it's not a mineral defincincy that's for sure.
It's either lack of nitrogen or spider mites. Inspect plant for webbing. While you're at it look for other insects, too.
What type of food do you use to feed your citrus? Feed w/a food high in nitrogen. like 10-5-5 etc. You can even alternate w/miracid then Azalia or citrus food. Toni

Hmmm, I have the very same problem, the leaves look identical. I saw no mites, as I had checked closely, but, eventually the many leaves went yellow rapidly and then fell off, some did not higher up on the tree. This was a month or two ago, now the tree is outside, and grew several new leaves and buds, but the newer branches are weak and the leaves are thinner and not as green. I changed the potting material to an orchid mix/potting soil that is not supposed to hold water and it drains well... I am stumped. I did have some scale, nothing too bad and I cleaned them off with alcohol including some leaves, I thought maybe that caused the yellowing.. I check for new scale weekly.

Toni,

I am interested in why you say it's not a mineral deficiency, I, who is not knowledable about plants, would have thought it was, so I used azeal..azail..aezal..rhodadendron fert. I would like to know for the future, what makes you say it's not a deficiency?

The whole overall tree pic should be in order. 3 leaves just not enough to determine the cause.
When citrus are blooming that's when the most OLD leaves drop to replace them with new. Spring time is when most citrus old leaves drop so it's natural.

I have had a similar problem with leaves turning yellow and dropping in March. I live in Ottawa Canada so my lemon tree is housebound from October to April or May. I have had a problem with scale both winters I have brought it in. I used a Later's Insecticidal Soap solution to clear out the scale (with reasonable success). I have just moved it out (cautiously with an eye to the overnight low!!) and I now have a few new leaves coming out but, overall the plant is not nearly as healthy as when I bought it 3 years ago. Any hints would be greatly appreciated because we love the blossoms AND the fruit so I don't want to give up on it!
Would the salts from a water softener be harmful to the plant?

Toni, thanks for the response, I checked for webbing and insects and have found none. I feed with Miracid Azelia food, its 30-10-10. I havent been giving it much over the winter becasue it was inside but I will give it a full dose today I guess.

dougsinc- I'm pretty sure the salt from the water softner isnt too good for your plant, If the salt builds up It can hurt it. I'd flush it out with the garden hose for a few mintues, just let the water run through the pot for a while- Thats what I'd do but I'll let someone else handle that in case I'm wrong.

Storm, the reason I say it's not a mineral definciency is, if you've ever seen pix of plants w/this problem you'll note veins are pronounced..they're really green while the inside of the leaf is pale to yellow.
I've seen this happen w/a hibiscus I hadn't treated that yr for iron. I usually apply iron 2-3 times a yr and so far, cross my fingers, have not had that problem since the hibiscus fiasco.
I wish I knew of a site that displayed mineral defincies, but I don't..Perhaps someone else knows of one.

Scale will cause yellow and deformed leaves..Most insects that suck leaves will also cause yellowing of leaves.
But lack of nitrogen also causes leaves to yellow. That's why my suggestion is to first check for insects, and if this isn't the case then apply a fertizer high in nitrogen. Toni

Heres a link to a page with pics and descriptions

Here is a link that might be useful: deficiency pictures