I'm guessing that your tree is very under watered. You're watering according to the typical (but not very plant friendly) cycle: frequent, but shallow. Plants prefer deep watering, done on an infrequent schedule.

A 15 minute irrigation cycle is not enough to get water much deeper than an inch or so (if that).

Though it's important not to over water citrus, they still require occasional deep watering in order to stay healthy. I'd suggest that you water your tree by hand once a week, deeply.

Do you fertilize your Lawn...? Could be, just could be that your front yard trees are getting more Nitrogyn than the back ones from your lawn fertilizer leaching into the soil. Remember, Citrus trees are HIGH Nitogyn lovers, as well as aother nutrients. I had a friend in Florida that this happened to. Without looking at pictures, this is just a guess. There are many things that can turn Citrus trees yellow, but there is different kinds of yellow, like leaf veining, leaves that are a light green, and leaves that are just all yellow. Hope this solves your problem.;-)

Well, everything I've read says that citrus do not need much irrigation, that they prefer to be drier rather than wet. I do check the soil between waterings, and even though the top layer dries out, if you dig your fingers down a few inches, you still find some moisture. It's not real wet, but you can still feel some moisture, so I would think this would be ok for trees that prefer not to be too wet. I do fertilise the trees about 4 times a year, whenever the new growth flushes begin. I fertilise the lawns (Floritam) with scotts bonus s weed and feed, but I follow scotts directions and never apply closer than 15' to the dripline of the fruit trees. The thing that makes me not think it's a water issue is that the trees in the front yard are in the same type of soil and on the same irrigation schedule, and they are wonderfully green and healthy, and loaded with growing fruit.
Dave

Dave, it's true citrus need to dry between waterings, but when they're originally watered, citrus need a hearty drink.
You said the trees are on the same irrigation schedule, by chance is the back is getting more sun than the front?

Specific nutrient defiencies, (mainly caused by high soil pH) produce Chlorosis which may be corrected by supplemental feedings of iron, magnesium or nitrogen compounds in various combinations.
BTW, some pesticides, including herbicides, can cause Chlorosis.
Good luck, Toni

Weed and Feed products can do serious damage to trees and shrubs. Plant roots extend MUCH further than the 'drip line', so we may have a real possibility as to what is doing the damage.

Yes, I know that atrazine will kill trees and shrubs. That's why I do not apply close to any of my fruit trees. The directions say do not apply beneath the branches (dripline) of trees, but I stay a good 15 ft away from the dripline of the trees with these products. Other people we know in this area use them in a similar fashion with no ill effects on trees and shrubs. The cirus in the front yard also receive full sun, the same irrigation schedule, and the lawn receives the same care.
Dave

I have an orange tree just like yours that is slowly failing - yellow leaves and browning branches . Last year I took a branch to the Ag Center and they said - no known reason why it's declining - that just happens sometimes . It's incompatible with life .
A year later- the tree bloomed , set fruit but continues to yellow . I do NOT use any weed & feed .
One expert said they have seen many types of trees fade away due the stress of several hurricanes followed by now three years of drought . They recommended cutting the tree down and replacing it with a healthier one . It might just come to that !

I don't know if I wrote before but have had the same problem with my trees for years and last year I think we overwatered and all the blossoms and fruit fell and what was left split. This year I am misting with liquid Kelp and it is amazing, not dark green yet but leaves everywhere, thousands of new growth, amazing flowers and blooms that never fell off the tree for the first time in years. We had so many dry branches and they too are leafing. Look close for disease because that too was present before and I got a liquid for disease and bugs in a beige plastic that just took care of that right away. Now if the ants will go someplace else we're going to have lots of fruit in the winter. Last years growth which there wasn't alot is so sweet. Kelp seems to be helping everything in my garden this year..

There is a particular disease that is suppose to be hard to diagnose because it stays latent for a couple years and some of the new foliage have symtoms that look like a zinc or manganese deficieny with yellow venation.

The most characteristic symtom is a blothy mottling of leaves and the leaf yellowing that may be on a shoot or new flushes being yellow. No doubt your leaves need to be viewed at the molecular level, especially because you are in FL.

A very good pic. of the insect that transmits the disease is found at: ag.arizona.edu/crops/citrus/greening_pest_alert_fl.pdf

Lots of good pics. & inf. can be found at: aggie-horticulture.tamu.edu/citrus/diagnostic/greening/greening.htm