I would counsel against the extension. They merely do the NPK and a couple others. From the looks of things, it looks like the imbalance is more severe. That's why I suggested Logan Labs. They are more expensive, but it really does pay off in the long run.
I've done extensive posts on balancing soil. If you are interested, I can repost the links.
Logan Labs is going to get expensive quickly and this plot isn't even ours... so then I'd have to do it again when we move...
Let me explain the situation here in central Wyoming.
We don't have lovely loam soils here. They don't exist. (The closest good soil is 2 hours away.) The nice areas here have sandy clay. The bad areas are not even worth trying to garden on.
Our soils are on the edge of an alkali flat. It's not good soil, it's not a gardener's friend. This is true for our whole area. People have spent loads trying to remediate the soil in our area - to no real gain. I even asked at the extension office and the guy was very pessimistic about growing anything in the soils around here.
The answer appears to be to grow on top of the soil rather than spend loads and loads trying to remediate something that isn't going to be fixed.
Why spend hundreds of dollars we don't have on extensive testing (and then do it again when we move) when I can spend the money on building raised beds (simple frames that can be moved is all I'm talking about at the moment) and trying to put some organic matter into this soil?
I'm not going to give up - I will work with the soil, as well as on top of it... but I wanted you to understand that it's not a simple balancing act here, but something far more difficult that even the experts are struggling with.
How many gardens do you have? I have 3/4 of an acre, in 3 large gardens and it costs me $90/year for testing. it's been worth its weight in gold, to have the tests and amend exactly what is needed.
But if the soils are that bad out there and the land is not yours, then perhaps raised beds is the answer. It really limits how much you can plant though...
By alkali, do you mean you have real high calcium? This is outside my experience, as calcium is not an excess here...
Alkali flats are what's left after a lake evaporates or otherwise drains. It's salty and nasty. It's also strongly alkaline. That part is relatively easy to remedy compared to the salt and other toxins in the soil. The guy at the extension office was talking about how they had even done a study on how to remediate some of the worst of it... and nothing helped.
Actually, until I talked to him, I felt similar to yourself - that surely, there's something that can be done... I can work with the soil, rather than against it... Now, I'm not so sure.
Where it's not alkali, it's very sandy and doesn't hold water. Even with addition of organic matter, it doesn't keep the water very well. (That was also talking to a master gardener in our area.)
So, yeah, I think raised beds (along the lines of hugulkultur) will be key. I was never intending to do a market garden anyway - just enough for ourselves and maybe a little to barter.
We have exactly 1 garden (currently 12 beds including
the one I have the fennel in) and again not our land... maybe we'll inherit it, but maybe not, we don't know at this time.
If all the beds have been used the same way, and were created in roughly the same time, you might be able to do just 1 test.....
I know about how sand holds organic matter. This sandy loam I have here will release the organic matter really quickly if I don't keep it covered. I have what was a top soil pile for re-making the flowerbeds, and it's been sitting a year now. It looks like subsoil....