Lemon tree with yellowing leaves

One Of My Greenhouse Lemon Trees(with Green Lemons On It) Has Many Leaves Turning Yellow. What Could Cause This,please, And How Do I Correct It? Thanks

 

There are a number of possibilities, most likely is some kind of deficiency. Here is a link to help diagnose deficiencies.

http://edis.ifas.ufl.edu/CH142

The only other possibility I know would be root rot from overwatering--however it is normal for some older leaves to turn yellow and drop.

Skeet

 

This is the prime time of year for citrus to discard their old leaves. Is the yellow starting along the center vein towards the bottom center?

Millet

 

No,the yellowing seems to be starting from the outside and tips.

 

If the yellowing has developed on the tips and margins of the leaves, the problem is either a mineral deficiency or high soluble salts in the root zone. If it is from high soluble salts, there should be some burning/drying on tips and margins. If it is from a mineral deficiency, than the leaf will still have a normal soft flexible consistency but will be chlorotic.

Millet