Soil and Forage Testing Laboratory at Auburn University

Alabama Soil Health Index

Soil health is the ability of soil to perform functions that support life on earth. Soil provides food, fiber, and energy to sustain human life. Soil also protects our natural resources by filtering water and decomposing harmful chemicals.

Properties of a Healthy Soil

  • High organic matter content
  • Optimal nutrients and pH for plant growth
  • Stable soil aggregates to promote water infiltration
  • Large population of beneficial organisms
  • No contamination

Many soils in Alabama could be considered unhealthy due to severe erosion, low organic matter content, and intensive farming practices historically used in the state. It is important to rebuild soil health to conserve this natural resource for use by future generations. Practices such as reduced tillage and cover cropping can increase organic matter and improve soil health in Alabama.

What is included in the Alabama Soil Health Index test?

What is included in the Alabama Soil Health Index test?

  • Routine Soil Test: This includes soil pH, buffer pH for lime requirement, and extractable P, K, Ca, and Mg analyses.
  • Estimated cation exchange capacity and soil group: Cation exchange capacity (CEC) is the sum of exchangeable cations that a soil can adsorb. Cation exchange capacity is affected by soil texture, pH, and organic matter content.
  • Percent base saturation: Base saturation is the percentage of the CEC occupied by the cation form of calcium (Ca2+), magnesium (Mg2+) and potassium (K+), as opposed to acidic cations of hydrogen (H+) and aluminum (Al3+). Base saturation is affected by pH, and at extremely low soil pH (and base saturation), aluminum toxicity can occur.
  • Soil organic matter content: Organic matter consists of carbon-containing compounds from dead and living plant and animal materials. Soil organic matter increases nutrient- and water-holding capacity of soil and is an important indicator of soil health.
  • Soil respiration test: This 24-hour test is an indication of microbial activity in the soil and can be used to estimate potential mineralizable N from soil organic matter.
  • Aggregate stability: Aggregate stability is a measurement of soil structure. Stable soil aggregates increase water infiltration into the soil and are a good indicator of soil health. For this test, soils are classified based upon how well soil aggregates hold together in water.

How to Take a Sample for the Soil Health Index

  • Place soil in a routine soil test box just as you would for a regular sample but clearly mark it for SOIL HEALTH. Also mark the soil information sheet for "Soil Health". These samples will require special handling once they arrive in the AU Soil Testing Laboratory.
  • Do not sample extremely wet soils or very dry soils. For whole-field samples, collect a uniform slice or core of soil from the upper 3-4 inches of topsoil for pastures and / no-till soils in 20 or more random spots throughout the entire field. If the field is cultivated or plowed, take samples to the depth of tillage (usually 6 to 8 inches deep). Mix the subsamples in a clean, plastic bucket. Remove rocks, twigs, roots and vegetation.
  • Try to leave a few undisturbed clods or aggregates of soil intact for the "aggregate stability/slaking" test.
  • Samples can be taken at any time of year but are most beneficial in the months prior to crop establishment.
  • Submit samples to your county extension office or mail directly to:
    Soil Testing Laboratory
    ALFA Building
    961 S. Donahue Drive
    Auburn University, AL 36849-5411
    Allow 2-3 weeks from the time the sample arrives until all the analyses are completed. Results will be returned electronically if a valid email address is listed on the information sheet or a hard copy will be mailed to your address.

Interpreting the Soil Health Index

An example soil health report is pictured below. For each test measured as part of the soil health index, a maximum score has been assigned based on research which correlates a given soil test to yield.

Three color codes will be used for each value in the SQI, green for optimum, yellow for marginal, and red for needs improvement.

Recommendations are given in the "recommendations (REC)" column and in the "comments" section to suggest best management practices, such as cover crops and reduced tillage to improve soil health.

At the bottom of the report, the total "soil health index score" is given as a value between 1 and 100. Most Alabama soils will score between 40 and 80. The soil health index is most useful to assess how management practices are improving soil health over time. For best use of the soil health index, soil samples can be taken 1) from the same area over time or 2) for areas with a similar soil type and different management practices to assess whether management practices have a positive or negative impact on soil health.

Sample Soil Health Report
Factor Values Max Score Your Score Your Value REC
Soil CEC/Soil Group <4.6
(Grp 1)
(Grp 2)
(Grp 3)
(Grp 4)
  5 4 7.5  
Soil pH Very Acidic Acidic Optimal Alkaline   15 15 6.7  
P Rating VL/Low Med High Very High EXTR High 10 5 M 47 See soil test P REC
K Rating VL/Low Med High Very High EXTR High 10 10 H 221  
Base Saturation <10% 11%-25% 26%-50% 51%-75% >75% 10 8 85%  
Soil O.M % <1.0 1.0-1.9 2.0-2.9 3.0-3.9 >4.0 20 12 2.5% PP1, PP2, PP3, SP7
Soil Respiration
(Microbial Activity)
Very Low Low Mod High Very High 10 10 4.3  
N Mineralized
<10 10-20 20-40 40-80 >80 10 10 80-160  
Aggregate Stability No Agg Weak Mod Strong Very Strong Agg 10 4 3 PP1, PP2, PP3, SP7, SP2

Comments: Soil could use improvement. Consider implementing one or more of the above practices.

*Soil compaction and runoff may be a hazard with low aggregate stability. Consider reduced or no-till, high residue management, use of cover crops,and mulching. Consider in-row subsoil or strip tillage.

*Due to high N-mineralization, consider reducing N-fertilizer application by 30-50 lbs N/ac.

See BMPs Above

For more information on soil health, see our publication: Soil Health in Alabama