Reading & Interpreting Soil Test Reports
Part 1 – 436 | Unit 1.11
Lecture 1: Using a Soil Test to Assess Soil Quality
- Cation Saturation Ratio (CSR; also known as % base saturation): The CSR approach states
that there are optimal ratios and amounts of certain cation soil nutrients (e.g., calcium,
magnesium, potassium, and sodium) that when present in agricultural soils lead to greater
soil quality (physical, chemical, and biological properties), crop and animal health, an
increased resistance to pests and pathogens (pre- and post harvest), and increased crop
productivity. The % base saturation reflects the % of exchange sites on soil particles that
are “held” by the basic cations (Ca++, Mg++, K+, and Na+); the remainder of sites are held
by acidic cations (H+, Al+++). - Nutrient Build-Up and Maintenance: This approach calls for initial application(s) of given
deficient nutrients in quantities that will raise the soil level of those nutrients to the point
where crop yields are maximized. This is followed by annual amendment applications that
will maintain a non-limiting soil nutrient level. It is often suggested that such build-up be
done over a 2- to 4-year period. This approach emphasizes the major nutrients (nitrogen,
phosphorus, and potassium) and does not focus equally on all 13 essential plant nutrients. - Most testing services have established optimal ratios for general soil fertility that are
a combination of SLAN, CSR, and Nutrient Build-Up and Maintenance approaches. As
different testing services use different extraction techniques, it is import to consult
with your local testing service on the system they use in developing amendment
recommendations. Always request “best practices” benchmarks for maintaining soil quality
if different than above. Specify the crop or crops being grown, and let the lab know that
you are using organic techniques. Request “recommendations” when submitting a soil
sample for analysis. - If possible, use a regional soil testing lab, which will be familiar with your local soil
conditions
Note that different soils can require different nutrient extraction techniques, e.g., some are
developed for soils with a given pH range and will give misleading results for soils outside
of that range. Also, the presence of high levels of certain compounds in the soil may distort
soil tests and require different extraction techniques.
The specific nutrient levels listed in this unit are based on the extraction techniques used at
specific laboratories. Although over 90% of U.S. agricultural testing services use the same
extraction techniques, some variation exists.
Note: It is critical that one confirms the specific “optimal” levels used in this unit with those
used by your local testing service. The optimal levels presented in this unit are examples of
those used by many A & L National Agricultural Laboratories.