Soil Test Ratings or Interpretations

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:

RatingMeaning
Very LowLess than 50 % of the crop yield potential or esthetic value is expected without the addition of that nutrient. A plant response is expected!

LowSomewhere between 50–75 % of the crop yield potential or esthetic value is expected without the addition of that nutrient. A plant response is expected!
MediumFrom 75- to perhaps 95 % of the crop yield or esthetic value is expected without the addition of the nutrient. A plant response is expected!

HighA 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 HighA 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!

3/11/2010 7:40:09 PM
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