pH, alkalinity and salinity are three different things.
And, unfortunately, it can be quite confusing.

pH is how acidic or basic something is. It is a measure of the concentration of H+ ions in the substance. It's seems a bit backwards because the higher the concetration of H+, the lower the pH number.
Unfortunately, the term "alkaline" usually means something is basic (low concentration of H+ ions). But alkalinity is not the same as being alkaline.
For instance, my water is alkaline (ph of around 8), but it has low alkalinity.
Alkalinity is the measure of how well the substance being tested can neutralize acidity. This isn't the same as just being alkaline - for instance my pH 8 water has very little buffering and can swing to an acidic pH very easily. This can be a problem for my water garden. But if my water had high alkalinity, it would resist pH change. High alkalinity is the result of the substance containing lots of carbonates.
Salinity is salt content. You can have complete neutral pH and have high salt content. You can have high salt content and low alkalinity ( low amount of acid netralizing carbonates and hydroxides).

The rugosa rose is an example of a plant that has high tolerance of salinity, but is poorer than most other roses when it comes to tolerating soil with a high pH.

Oh, boy, Cnetter . . . if I can't figure this out - someone just telling me that my soil has a pH of 7.4 and the water goes over 8 pH every Summer or that a tomato variety has a high tolerance for salinity and might be a healthy plant in my garden - - isn't going to be helping me, at all.

Hadn't realized that "alkalinity is not the same as being alkaline" - another seeming contradiction of terms.

I had long felt that years of gardening and applying, say, 20 inches of irrigation water thru the growing season, would tend to move my soil towards a neutral pH. But, is that what is happening in places like the Sacramento Valley and many fields in Utah where salts are building up from irrigation? Surely, the deep wells here would have a good deal of dissolved minerals - which way would the soil be heading?

Does your water have a pH of 8 but without much in the way of dissolved minerals and, therefore, have less buffering? (Maybe you don't have to work very hard on that one since I don't have a water garden. ;o)

Promise, I'll study what you've already written and try to see some light . . .

Steve

Irrigation does tend to add to the salinity of soil. I think the way many people around here water their lawns is making it happen faster than it needs to happen. Too many people water too often and the salts tend to build up.

Also, I may be wrong, but I think irrigation water tends to make the alkaline conditions worse, as well. I don't quite understand cnetter's discussion on how alkaline and alkalinity aren't the same, so I may be using the wrong term here, but our soil tends to be alkaline to start and irrigation, especially done wrong, can make it worse.

"Does your water have a pH of 8 but without much in the way of dissolved minerals and, therefore, have less buffering?"

Basically, Yes. Although it is the lack of certain minerals that cause the lack of buffereing.

"Surely, the deep wells here would have a good deal of dissolved minerals - which way would the soil be heading?"

It depends on what the dissolved minerals are. If they are calcium carbonate (or othe alkalinity increasing minerals), then the alkalinity of the soil would increase, and since the acidity of soil is being neutralized, this would also up the pH over time. If the dissolved minerals are Sodium Chloride or Iron, then it wouldn't have an affect. Well, maybe... even that depends on what other chemicals are present. Could get sodium hydroxide. I *think* the fields in Utah that are having problems with salt crusts are heading alkaline, but salinity is the main problem I see discussed.
And salinity can be due to salts other than Sodium Chloride.

You're going to make me dig up my 28 year old chemistry books out of the closet. I'm really really REALLY rusty.

As Cnetter posted pH is a measure of the H+ ion concentration. The pH scale is a logrythmic scale going from 1( the most acidic) to 14 (the least acidic or basic)
Each difference in the scale means that there are ten times as many H+ ions as the number above. IE. a solution with a pH of 1 has ten times as many H+ ions as a pH of 2.
a solution with a pH of 1 has a thousand times more H+ ions as a solution with a pH of 4 (10x10x10. Alkalinity is measure of how well a solution will use up the H+ in solution or neutralize the pH. Solutions with lots of stuff dissolved in it that will use up the H+ ions will have a greater alkalinity than ones that don't have as much stuff eveb though the solution with less stuff may have a higher pH (more basic) Buffering capacity refers to a solutions ability to resist cahnges in pH. If you have lots of baking soda dissolved in water, it will take lots of acid to netralize it. A little baking soda, will only take a little acid. Both solutions would have the same pH, but the lots of baking soda would have more alkalinity, because it can use up more acid.

Salinity is a measure of how much stuff is dissolved in water. The reason salinity increases with irrigation is that as water evaporates it leaves the dissolved stuff behind increasing the concentration. If you have good drainage most of the dissoved stuff will stay in the water and get carried away.

Henry in Creede

Well, I've certainly got good drainage, Henry. And, that may be the "saving grace" for a tilled garden as opposed to grass turf, BPGreen. (You can tell from earlier posts that I'm always trying to let the lawn take care of itself - I'll be down to covering the yard with bark one of these days ;o)

And, I may well be (attempting to get Cnetter to ;o) over-analyzing the issue.

Increasing the gardens' organic matter should help in many, many ways but it is a continual struggle. After a year or two, it becomes nearly impossible to even find any material that has been added. I also argue with DW about how much of it I should be moving around in a wheelbarrow and what I'm doing with THAT shovel!

A good deal of work is being done by the seed companies to develop plant varieties that are "salt tolerant." I wonder how much that might be of help to all of us but, perhaps not. With a high enuf pH, apparently it becomes impossible to grow some plants without completely replacing the soil - imagine if we tomato lovers were faced with that dilemma! And, is this the reason for my problems with these tomato diseases in some varieties?

The U of Idaho notes that tomato growth occurs when the soil pH is between 5.5 and 7.5 but they do well (?) in Idaho where the pH ranges from 7.0 to 8. I thought I may be pushing it at 7.4 but the U of I putting it that way makes their statement rather unbelievable.

Calcium and magnesium are reported to be the primary causes of our water hardness. But, dissolved solids (downstream - not here) are far less than the 500 milligrams per liter safe level (about 150mg/l), we are assured.

Information on water seems to be deliberately couched to soothe the public. Reports do go on and on about how the water quality is good but, since the water is susceptible to contamination, more testing, monitoring, and reports are necessary. Remediation efforts to control contamination are indicated by how much $$ is spent on studies.

Steve
hearing demands from small seedlings . . .

"After a year or two, it becomes nearly impossible to even find any material that has been added."

Yes. The organic matter breaks down until it's humus and is only about 10% of what it was to start. You need to add it every year because of this.

Let me further confuse the issue and call "salts" the various chemicals that cause "alkalinity" when they're dissolved but then dry out and leave that white stuff. That crusty ring on the 3 year old potted plant container that looks like salt.

In the Great Basin / Inter mountain West, much of the place used to be a sea, and as that disappeared, it left concentrations of the various salts in the sandstone, clay, and other soils. Generally speaking, the top layer, where the plant roots are, is fairly well leached out. However, areas where natural run-off through porous soils will accumulate the salts, and thats where one finds the dead-cow skull by the pool of water in a white landscape, and the cowboy jumps of his horse, slurps the water, and then sez 'yuck' because it's so alkaline.

Irrigation in the inter mountain West can effect this in two ways, depending on the sub-soils. The irrigation water dissolves the salts, dispersing them throughout the soil. then the water evaporates, leaving a higher concentration of salt in the top layers. So, they irrigate more. Which causes more salt to come up. Thats why, at least around here, that the best farm land is on the tops of hills, or on a slope, where the irrigator can flush the stuff out and on down the river towards California.

On my place, which is on a slope, over the winter the irrigation water I put on in the summer seeps out on the lower reaches of the property, and evaporates. It leaves a white, crystalline residue, that just crumbles off the soil when I touch it.

I can't remember, but there is now some additive that the guys can use in the flats at the bottom of the hills, the places that accumulated all the leached out salts/akalinity-producing compounds from up the hill, the kind of places that only could support sagebrush. I was speaking to a local farmer who was telling me about this, but he really, really has to watch how much irrigation water he uses because just a bit too much on, the whole field turns white. Guy raises oats and hay.