Soil and Forage Testing Laboratory at Auburn University

Alabama Soil Quality Index

What is "Soil Quality"?

Soil quality, also referred to as soil health, is defined as how well soil does what we want it to do. Healthy soil gives us clean air and water, bountiful crops and forests, productive grazing lands, diverse wildlife, and beautiful landscapes. (For more information, visit NRCS Soil Health) The Soil Science Society of American defines "Soil quality" as "The fitness of a specific kind of soil, to function within its capacity and within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation".

Almost all soil scientists agree that soil quality issues are one of the main issues limiting sustainable farming systems. Most will also agree that in Alabama, a very high percentage of our soils would be considered "poor quality soils". This not only limits productivity but can result in increased water quality problems due to runoff, erosion hazards, and low quality production. Most Alabama producers are not aware of the fact that their soils need help. A few small-scale producers are adopting "organic" or so-called "sustainable" techniques to help them improve their soils. This test will help those producers who are interested in improving and monitoring soil quality.

Objective and Premises behind the Alabama SQI

The overriding objective of the Alabama SQI is to help Alabama producers improve the quality/health of their soils. To accomplish this, we used five premises in developing an SQI.

  1. The SQI should make farmers and gardeners aware of soil quality/soil health.
  2. The SQI should suggest ways of improving soil quality/soil health.
  3. The SQI must be adaptable to existing soil test methodologies.
  4. The SQI must be relatively inexpensive to run on traditional soil samples.
  5. The SQI must provide information in a simple, easy to understand manner.

What is included in the test?

The Alabama Soil Quality Index (SQI) is a series of both routine and non-routine soil tests which can be used to evaluate soil quality issues. It is not a comprehensive evaluation but it is related to conditions which exist for Alabama. It will not try to compare Alabama soils with soils in other regions of the U.S. The SQI is strictly a laboratory evaluation of a collected soil sample which may or may not represent the field or area of interest. It is subject to the same sampling errors associated with routine soil tests.

The test includes:

  1. A Routine Soil Test. This includes soil pH, buffer pH for lime requirement, and extractable P, K Ca, Mg.
  2. Estimated cation exchange capacity, base saturation, and soil group
  3. Extractable micro-nutrients and metals. The main purpose of this is to see if there has been any buildup of metals or micro-nutrients in the soil which could potentially create toxicities in some plants and have human health implications. Plant nutrients include Cu, Fe, Zn, Mn and B. Other metals include Pb, Co, Cr, and Cd.
  4. Soil organic matter. This value is usually low in cultivated, Alabama soils but is highly correlated with soil health issues.
  5. 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.
  6. Aggregate stability/slaking. Soils will be placed into one of four categories based upon how well soil aggregates (small clumps of soil) hold together in water. This is actually known as a "slaking test".
  7. Soil EC (electrical conductivity). This is usually quite low in Alabama soils. Moderate values usually indicate recent fertilization while high values suggest salt problems.

How should samples be taken?

Collecting samples for the SQI is very similar to sampling for routine analysis (fertilizer recommendations). In fact, you will receive a routine soil test report and nutrient recommendations as part of the SQI.

  • Samples can be taken at any time of year. Do not sample extremely wet soils or very dry soils. This could affect the analyses.
  • For whole-field samples, collect a uniform slice or core of soil from the upper 2-3 inches of topsoil in 20+ random spots throughout the entire field. If 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.
  • Place soil in a routine soil box just as you would a regular sample but clearly mark it for SOIL QUALITY. Also mark the soil information sheet for "Soil Quality". These samples will require special handling once they arrive in the Soil Testing Laboratory.
  • There is a $XX per sample charge for the SQI.

The Soil Quality Test is not suitable for grid sampling but may be applied to zone sampling where zones are about 5 acres each. Sample zones as for whole-field samples.

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 one week 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.

How are the results interpreted?

Results for each sample will be compiled on a single sheet or pdf form with traditional ratings of nutrients from "very low" to "extremely high". "High" would be considered the optimum value that a high-quality soil should achieve. Other factors will be placed into 4 or 5 categories and assigned a value (Fig. 1, 2). Three color codes will be used for each value in the SQI, green for optimum, yellow for marginal, and red for needs improvement.

The most important interpretation will be the total "SOIL QUALITY INDEX" (SQI) which will be given as a value between 0 and 100. Most Alabama soils will fall in the 40 to 80 range. A producer can use this index over time to assess how his production practices are improving overall soil quality. Inputs into the SQI may be adjusted over time. Recommendations/comments will be given for best management practices that can be used to improve each component of the SQI (Table 1). Web links to USDA-NRCS best management practices will have to be attached to the one-page SQI.

Linking Index to Conservation Practices

A critical part of the Soil Quality Index is existing conservation practices that can be used to improve soil quality. There will be two sets of practices recommended to improve soil quality:

  1. Primary Practices that would be recommended in all situations.
  2. Supporting Practices that would be recommended depending upon specific site situations and conditions (soil type, slope, operations goals and needs, etc.).

Primary Practices (PP)

Supporting Practices (SP)

Complete list of conservation practices. The conservation practice and/or an internet link to the practice will be included as part of the SQI.

Implementing the SQI

Most producers should be able to use the SQI without additional help or assistance as long as they are able to gain access to USDA-NRCS web sites where the best management practices are listed. At some point, these may be included on the AU Soil Testing Lab website along with this training material. Cooperative Extension agents, NRCS Conservationists, consultants and Certified Crops Advisors (CCAs) will be a valuable asset in incorporating field observations and field measurements into the SQI.

The Alabama Soil Quality Index - Example Report (Fig.1)

Factor84ValuesMax. valueYour ScoreBMP recommended
Soil CEC/soil group<4.6 (Grp 1)4.7-9.0 (Grp 2)9.0- 15.0 (Grp.3)>15.0 (Grp 4)    
2455 55 
Soil pHw<5.05.1-5.85.9-7.07.0-8.0>8.0   
Base saturation<10%11-25%26-50%50-75%>75%   
Soil O.M.(%)<0.50.6-1.01.1-2.02.1-3.0>3.0   
N mineralized (lb/a)<1011-2021-3031-50>50   
Soil respiration Very LowLowModerateHighVery High   
Aggregate stabilityNo aggregatesWeakModerateGoodVery strong aggregates   
EC (1:2) Mmho/cm<0.400.40-0.800.81-1.601.61-3.20>3.20   
MetalsTwo or more metals "very high"One metal is "very high" All metals optimum   
TOTAL SOIL QUALITY INDEX10084Continue with existing practices

Comments: Soil Quality Index is high. Continue with existing practices.

Fig. 1. (Above) Example of a high quality soil from a well-managed cotton field in the Tennessee Valley of North Alabama. SQI = 84

The Alabama Soil Quality Index - Example Report (Fig.2)

FactorValuesMax. valueYour ScoreBMP recommended
Soil CEC/soil group<4.6 (Grp 1)4.7-9.0 (Grp 2)9.0- 15.0 (Grp.3)>15,0 (Grp 4)    
2455 52 
Soil pHw<5.05.1-5.85.9-7.07.0-8.0>8.0  Apply Ag. lime at recommended rates
Base saturation<10%11-25%26-50%50-75%>75%   
Soil O.M.(%)<0.50.6-1.01.1-2.02.1-3.0>3.0  PP2, PP3, SP3, SP7
N mineralized (lb/a)<1011-2021-3031-50>50  Building soil organic matter will help.
Soil respiration Very LowLowModerateHighVery High  Building soil organic matter will help.
Aggregate stabilityNo aggregatesWeakModerateGoodVery strong aggregates  PP1, PP2, PP3, SP7, SP2
MetalsTwo or more metals “very high”One metal is “very high”All metals optimum   

Comments: Soil could use improvement. Consider implementing one or more of the above practices. Soil compaction and/or runoff is a hazard. Consider reduced or no-till, high residue management, use of cover crops, and mulching. Consider in-row subsoiling or strip tillage.

Fig. 2. (Above) Example of a sandy, eroded, cultivated soil from the Southeastern Alabama Coastal Plain. SQI = 52

Table 1. (below) Interpretation and comments to be used with SQI.

Comment on reportNRCS practice
If SQI > 80Soil Quality Index is high. Continue with existing practices 
If pH < 5.8Add Ag. lime at recommended rates 
If P=EHP is excessive and additional P in fertilizers or manures should be avoided. 
If P value = VL or LConsider using animal manures to build soil P (PP4)PP4
If K = VL, L or M See soil test K recommendations
If SOM = < 1.0%Consider residue and tillage management and cover cropsPP2, PP3, SP3, SP7
If N mineralized > 50 lb/aConsider reducing commercial N applied by 30 to 50 lb. N/acre 
If aggregate stability is moderate or lessSoil compaction and runoff is a hazard. Consider reduced or no-till, high residue management, use of cover crops, and mulching. Consider in-row subsoiling or strip tillage.PP1, PP2, PP3, SP7, SP2
If N mineralized < 20 lb N/acreBuilding soil organic matter will help increase mineralizable N. 
If respiration is VL or LBuilding soil organic matter will help improve soil respiration. 
If one metal is VH CAUTION. Zn, Cu, Cd, Pb, or Cr is very high. This could be an indication of contamination from micro-nutrient fertilizers, manures or some other application. Metals cannot be removed from the soil. Keep soil pH above 6.0 to reduce metal uptake by plants. 
If 2 or more metals are VHWARNING. This soil has been contaminated from excessive metal application either from fertilizers or some other application. Metals cannot be removed from the soil. Keep soil pH above 6.0 to reduce metal uptake by plants. 
If 50 < SQI < 80Soil could use improvement. Consider implementing one or more of the above practices.See BMPs above.
If SQI < 50Your total soil quality index is low. Use one or more of the following primary practices to help improve the soil quality index. Re-test your soil in 3 years to determine if the practices are helping. You may be eligible for assistance from your local Soil and Water Conservation District Office or USDA-NRCS office.(list of NRCS Primary and Secondary practices)