I've been playing with the idea. I think I will have to do that...

The quality of water used to irrigate citrus is very important. Citrus trees are sensitive to high soluble salt concentrations (hard water), both for in ground trees, and container grown trees -- especially container trees. For container growers, soluble salt contaminates normally come from the irrigation water that is being used. The damage that can be done by the continued use of water with high soluble salt concentrations are, among the many problems that it causes, is the reduction of fruit that the tree will/can produce. A poor harvest, or no harvest at all, after a years effort is very depressing to a hard working and hopeful grower. The damage done is directly related to the Electrical Conductivity (EC) of the irrigation water. EC is a measure of the level of an electric current that will pass through a solution, depending on the amount of soluble salts that are dissolved in that solution. The EC can be easily found by using an EC meter. Many EC meters also are combined with a pH function. The decreases in the amount of fruit a citrus tree will produce due to soil salinity, (soil salts contaminate), are:

EC reading of 1.7 or lower is a reduction of O% (No decrease of harvest)
EC reading of 2.3 results in a 10% reduction of fruit at harvest.
EC reading of 3.3 results in a 25% reduction of fruit at harvest.
EC reading of 4.8 results in a 50% reduction of fruit at harvest
EC reading of 8.0 results in the loss of the entire crop. (No harvest)

Millet

Millet, nice informative thread.
I saw this comment of yours elsewhere on the site and I believe it is relevant to the discussion here:

Millet wrote:

It does look like a manganese deficiency. The deficiency can be corrected by applying Manganese sulfate or manganese chelate. This condition can also be brought on by long term irrigating with water high in bicarbonates.

Is the source of this deficiency not necessarily the presence of the carbonates, but soil pH? Where at high pH (resulting from accumulated carbonate salts), the Mn (along with possibly a few other nutrients) is no longer available to the tree? Any high pH water source (whether or not it is high in carbonates) could potentially cause this, correct? I believe many municipal water sources have their pH adjusted to somewhere between 8.0 and 9.0. This is done to reduce its corrosiveness and minimize the likelihood of lead leaching from old pipes.

Shouldn't flushing container citrus with several volumes of water 4-5 times per year minimize the probability of excess carbonate (and other soluble salt) accumulation becoming a problem.
Or am I missing something?

Also, regarding the EC soil readings, are the reduced crop yields at high EC readings primarily the result of increased osmotic stress? It is my understanding that "salt" stress/toxicity, primarily from accumulation of chloride ions in the plant tissues, can happen at lower concentrations of soluble salts than is necessary for osmotic stress to become a factor.

Tom, your above thoughts are correct, and stated very clearly. The safe levels of bicarbonates in water for long term irrigation is 50-PPM (it is actually claimed to be 100-PPM). My deep well's water contains 200-PPM. After continued irrigation with this well water, my trees started to show numerous problems. The fruit production became minimal, and foliage damage and growth restriction were obvious. After simply switching to rain water, the problems cleared up within 6 months. In a 55-gallon drum I now use 10-gallons well water blended with 45 gallons of rain water.- Millet

The amount of water an in ground orange tree can use during a July day.

The size of a citrus tree and variety determines its high summer water usage in July:

Oranges - 8 feet spread - uses 10 gallons of water per day

12 feet spread - uses 22 gallons of water per day

16 feet spread - uses 39 gallons of water per day

20 feet spread - uses 60 gallons of water per day

Grapefruit and Lemons use about 20 percent more water than the amount needed for oranges. Water needs for mandarin/tangerines is about 10 percent less than that for the orange.

Millet

As a citrus tree with mature fruit nears harvest time, giving the tree MODERATE water stress increases the sugar (Glucose & Fructose) content in the juice sacs, thus producing a sweeter fruit. - Millet

Click the like below and scroll down the page for a pretty cool water usage calculator based on tree height:

http://128.227.177.113/ACPS/Data.html

Best,