Home soil test kits can be expected to provide a reasonably accurate soil pH reading (when using distilled water). But they are worthless for assessing nutrient levels or mineral deficiencies. For that you need a professional testing lab. Even many of those do not test for nitrogen levels, as it is difficult to generate an accurate reading for more than a moment in time. It can and will vary widely.

That's a rather discouraging answer. I asked Google about soil analysis services for homeowners, and its AI agent told me that typical costs are $700 to $1800. I assume that's for a single sample. I found one service whose web site specifies that it's intended for homeowners (most apparently don't say), and it said $186 for a basic analysis, $286 for a more comprehensive one. The simple analysis would satisfy me, but testing my five samples would cost $930. And I intended those five to be an initial trial of the testing process. My property is hilly, and extensively graded and "improved"; it would be naive to assume that the results from any one part would tell me anything about others.

It looks like I'll have to settle for the test kit results, no matter how inaccurate they are, or just go with my gut. My gut tells me that my soil is generally short of nitrogen, and that I won't be able to tell what else is wrong until I correct the nitrogen deficiency and see how things grow.

The lab I found was this one. I know nothing about them except what's on their web site. I mentioned them because I searched for something like "soil analysis lab for homeowners," and they're the first match I found that actually mentioned homeowners.

Do you have a recommendation? I'm seeking one because the amount of difficulty I had finding this one, plus its high prices, suggest that my common sense is not going to be a reliable guide in this area.

https://soiltesting.tamu.edu

https://ag.umass.edu/services/soil-plant-nutrient-testing-laboratory

Here's who I've used: https://umaine.edu/soiltestinglab/

Thank you... your suggestions made it plain that this is something ag services do, so I'll check out U.C. Davis, which is actually local for me. If they don't have such a service I'll use one of the ones you suggested.

The CA extension service does not provide soil testing. But it does provide a list of independent testing labs that do.

https://ucanr.edu/sites/newinyomonomg/files/323581.pdf