The soil came from a hedgerow bed planted many decades ago. When I acquired it 4 years ago the hedge was plainly sick. Judging by stuff left behind in the garden shed, maintenance had consisted of heavy fertilizing with a variety of "balanced" NPK fertilizers and other stuff, heavy shallow watering, and removal of all organic debris from the property.

I decided right off the hedge was going to go, and I did not water it. Most of the stems died. The stems were 1-3 inches diameter at the base, but digging them up I found root crowns 6-12 inches in diameter and riddled with rot, in soil barely 6 inches deep.

The soil test from this bed: pH okay, 0 N, too much K, and a P test result so extreme that the color was dark blue violet. The range on the test chamber is yellow to light blue green. So I am looking at remediating phosphorus toxicity, or?

Looks like I need get a laboratory soil test that includes zinc and iron. What else?

You don't mention what part of the country you are from, but it would be worthwhile seeing if your state's extension department offers reasonable, reliable soil testing.

The N test in this kit apparently isn't testing for ammonia nitrogen, because it does not indicate high N for household ammonia.

Without participation in a 3rd party conformity assessment program, there is no assurance that laboratory test results are reliable. If you doubt the reliability of home test kits, you should also doubt the reliability of laboratory test kits.