Interpretation of Soil Test Results (Agronomic Crops)

At the far left of the INTERPRETATION section are definitions for the “Soil Texture Code”. The Code lists the soil types contained in the broad classifications of “Coarse”, “Medium”, and “Fine”. You will refer to the Soil Texture Code when the texture of your soil is classified in the SOIL TEST RESULTS section.

The next three columns in the INTERPRETATION section graphically illustrate the relative levels of organic matter, soluble salts, and acidity in your soil, along with the buffer index. The graphs use stacked letters to form bar charts and they refer to the categories just below them in the SOIL TEST RESULTS section. In this case “Organic Matter” has five stacked O’s, which tells you that the amount of organic matter is medium in this soil. “Soluble Salts” were not measured, but there is a stack of two H’s above “pH”, telling you that the soil is moderately acid. A category related to pH is the “Buffer Index”, which has four stacked B’s and tells you that the Buffer Index is just below the intermediate level or slightly acid. The Buffer Index is measured only if the pH of a mineral soil is less than 6.0.

The rest of the INTERPRETATION section is not separated into columns, but it follows a similar graphical format that illustrates the relative levels (from “very low” to “very high”) of plant nutrients that were tested for in this soil. Once again, they refer to the categories just below them in the SOIL TEST RESULTS section. In this case, there is a stack of five P’s above phosphorus and a stack of 6 K’s above potassium, indicating that the soil tested in the medium range for both of these major plant nutrients (P is the chemical symbol for phosphorus and K is the chemical symbol for potassium).

Soil texture, organic matter, pH, buffer index, P, and K are part of the Regular Soil Test Series and are the usual categories tested. The nitrate (NO3-N) test is a standard practice used to adjust nitrogen fertilizer recommendations for a variety of crops in western Minnesota and is used in some situations in other parts of the state; see Using the Soil Nitrate Test in Minnesota. Soluble salts and the rest of the plant nutrients listed on the report are tested for only under specific circumstances where a problem is suspected or likely to occur. These circumstances include certain soil types and crops which are more prone than others to develop deficiencies of specific nutrients. See the University of Minnesota Extension bulletin Fertilizer Recommendations for Agronomic Crops in Minnesota for more information on crops and soils where soil tests in addition to the Regular Series are recommended.