| Macronutrients | Units | Very Low | Low | Medium | High | Very High |
|---|---|---|---|---|---|---|
| Phosphorus | pounds/acre | 0-24 | 25-45 | 46-71 | 72-137 | >137 |
| Potassium | pounds/acre | 0-40 | 41-81 | 82-145 | 146-277 | >277 |
| Magnesium | pounds/acre | 0-45 | 46-83 | 84-143 | 144-295 | >295 |
| Calcium | pounds/acre | 0-615 | 616-1007 | 1008-1400 | 1401-1790 | >1790 |
Notes
Values for soil test categories are specific to the extractant used, in this case Mehlich-3.
The "high" category is considered optimum fertility. Categories "very low", "low", and "medium" are below optimum; "very high" is above optimum (excessive).
| Micronutrients | Units | Critical Level | High |
|---|---|---|---|
| Zinc | ppm soil | 1.0 | 50 |
| Copper | ppm soil | 0.5 | 20 |
| Boron | ppm soil | 0.5 | 20 |
| Iron | ppm soil | 50 | 100 |
| Manganese |
pH dependent: calculate an activity index MnAI = 101.7 + 3.75Mn - 15.2pH |
25 | 100 |
Notes
Micronutrient categories are less well defined than macronutrient categories. Values below the "critical level" should be considered deficient; values above "high" should be considered a warning. Certain micronutrients can be toxic to plants at excessive levels.
In addition to its effect on manganese availability, soil pH also affects availability of other micronutrients. Aeration can also be a factor. See Micronutrient Statements or specified fact sheets for more information.