Tests for soil salts and nutrients look at soluble minerals in your soil.
Soil Salts
The usual salt that causes problems is plain old table salt, sodium chloride. It poses a problem in some arid climate areas, and places with poor drainage. The other soluble salts that can cause problems are excesses of fertilizers. Excess fertilizers are seldom a problem in the ground unless you’ve had a fertilizer spill, but sometimes occur in containers that aren’t leached enough.
All salts cause the same basic problem; they make it difficult for plants to take up the water they need, even if the soil is moist. As a result, leaf tips burn and plants wilt and grow poorly.
Soil salts must be tested in a laboratory. The test is simple, but the equipment is too expensive to keep at home. Many soil tests routinely check for soil salts, especially in regions where they are a problem.
Fertility
Farmers and commercial landscaper maintenance teams check their fertilizer levels frequently with soil tests. These tests are an excellent way to give your plants just the fertilizer they need without wasting it.
However, the tests are tricky to carry out properly. The availability of plant nutrients depends on a complex set of factors, including the soil chemistry and the makeup of the clay portion of the soil. For that reason, the kits sold to home gardeners are difficult to use accurately.
Fertility tests performed in laboratories are quite accurate and sophisticated.