Tissue testing has several weaknesses just as soil test do.

A tissue test will report the one element that is limiting productivity of that crop.
In my case the first one was copper.
Take care of that and then the next element will make it's self known.
In my case that was Molybdenum. (always have trouble spelling that)
Then the third element makes it's self known.
In my case that was potash.

To be fair when I looked at the ratios, from the very beginning tissue testing was telling me I needed potash. Problem was I believes a Very High Soil test meant what it said.

There are many interactions between fertility elements. I early found Cu & Mo will do things to each other. Add Cu and the Mo level tissue level will go down. Much as applying heavy amounts of phosphate fertilizer will depress the zinc uptake, unless some zinc is also applied.

By trial and error I found, here, using some Sulfur Potassium Magnesium, locally known as K-Mag, will improve the uptake of potassium fertilizer, (0-0-60).

Soil testing problems.
Labs seldom use Olsen chemistry on acid soils, but they will use their Mehlich or Bray chemistry on calcareous soils. Therefore I must point out that my soil will be in the 8 pH range and for then to use the Olsen chemistry. Every time!
Add to this the labs will not routinely look at the level of free lime in the soil so we can adjust the amount of phosphate required. They all know calcium will form an unavailable calcium phosphate, rapidly after application.
There are numerous charts and graphs that hint that the higher the soil CEC the higher the reported Potassium level must be for K availability. Has to do with the clay particles attracting cations.
The deal is most labs like to say no potash is required with a 140 or a 170 ppm K.
This is where tissue testing shines, it will calibrate your soil test values. With my soil at a 40 CEC, if the soil test is less than 380 ppm K the tissue test will be deficient. (Unless of course there are two elements that are even more deficient). This soil will show some response to potassium fertilizer up to 500 ppm K.

Most soil test only for nitrate, and ignore nitrite and ammonium. Most soils are probed to 6 maybe 8 inches. Nitrates can be found below these depths. Result less nitrogen than is available is reported.

To be fair, my lab reports excessive tissue nitrogen in my alfalfa, when I know that it translates to 23 maybe 26% CP. Normal for the stage the plants were sampled. Also normal for the top 6 inches of alfalfa, rather than the entire growth.

Hopefully you can avoid more than 20 years of trial and error and constant study by using a consultant who understands your crop, your soil, your climate, and your management style.

My focus has been on this Central Texas climate, with our heavy clay soils, and staying focused on alfalfa for hay and bermudagrass for hay.

Have a Grand & Glorious Season.