Just a little word on lab tests;
Be sure to use an accredited lab. I've had quite a lot of testing done on a variety of soils and substances. There was a local Ag lab which did typical testing for years. All the farmers counted on it. I had testing done by them which was out to lunch. I started sending samples to the Bodycote group instead and was pleased with cheaper accurate results. There are other good labs but just check their accreditation.
I wonder if there is more value in plant tissue testing?