J Stevens
Retired Associate Professor and Extension Soil Specialist
Most soil testing laboratories use some form of rating scale within which soil test values are placed. On a Soil Test Results sheet, you see a table of values for soil pH, Phosphorus, Potassium, Calcium, Magnesium, Sodium, Sulfur, Copper, and Zinc.The nutrient values are given as ppm/ parts per million. To the right of these nutrient values are the ratings or interpretations for that particular nutrient or item, such as pH.
What do these ratings mean to you and your clientele?
The LSU AgCenter Soil Testing and Plant Analysis Laboratory (STPAL) utilizes a common rating scale. An example of this is as follows:
Rating | Meaning |
Very Low | Less than 50 % of the crop yield
potential or esthetic value is expected without the addition of that nutrient.
A plant response is expected! |
Low | Somewhere between 50–75 % of the crop yield potential or esthetic value is expected without the addition of that nutrient. A plant response is expected! |
Medium | From 75- to perhaps 95 % of the crop
yield or esthetic value is expected without the addition of the nutrient. A
plant response is expected! |
High | A yield increase to the added
nutrient or an increase in esthetic value is not expected. The soil can supply
the entire crop nutrient requirement for both the vegetative and reproductive
stages of development. No need to fertilize with that nutrient! |
Very High | A yield increase or increase in
esthetic value from adding that nutrient is not expected. The soil can supply
much more than the entire crop requirement, and still contain a reserve of that
nutrient for the next crop. No need to fertilize with that nutrient! |
Please keep this information readily available, using it to explain what these ratings mean.
Keep this in mind, the ratings mean more than the numerical values that are reported!
The LSU AgCenter and the LSU College of Agriculture