United States Department of Agriculture
Natural Resources Conservation Service		 Soil Quality Institute Go to Accessibility Information
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Soil Quality Assessment

Overview

Soil quality is an assessment of how well soil performs all of its functions now and how those functions are being preserved for future use. It cannot be determined by measuring only crop yield, water quality, or any other single outcome.

Soil quality cannot be measured directly, so we evaluate indicators. Indicators are measurable properties of soil or plants that provide clues about how well the soil can function. Indicators can be physical, chemical, and biological properties, processes, or characteristics of soils. They can also be morphological or visual features of plants. Useful indicators:

  • are easy to measure,
  • measure changes in soil functions,
  • encompass chemical, biological, and physical properties,
  • are accessible to many users and applicable to field conditions, and
  • are sensitive to variations in climate and management.

Indicators can be assessed by qualitative or quantitative techniques. After measurements are collected, they can be evaluated by looking for patterns and comparing results to measurements taken at a different time or field.

Examples of soil quality indicators:

Indicator Relationship to Soil Health
Soil organic matter (SOM) Soil fertility, structure, stability, nutrient retention; soil erosion
Physical: soil structure, depth of soil, infiltration and bulk density; water holding capacity
 Retention and transport of water and nutrients; habitat for microbes; estimate of crop productivity potential; compaction, plow pan, water movement; porosity; workability
Chemical:  pH; electrical conductivity; extractable N-P-K Biological and chemical activity thresholds; plant and microbial activity thresholds; plant available nutrients and potential for N and P loss
Biological: microbial biomass C and N; potentially mineralizable N; soil respiration. 
 Microbial catalytic potential and repository for C and N; soil productivity and N supplying potential; microbial activity measure 

 

Soil Quality Indicator Information Sheets

The following documents require Adobe Acrobat

Soil Quality Indicator Guide Sheet (PDF, 740KB) - A How-to Guide

Physical Properties

Aggregate Stability (PDF, 380KB)
Available Water Capacity (PDF, 210KB)
Bulk Density (PDF, 340KB)
Infiltration (PDF, 315KB)
Slaking (PDF, 500KB)
Soil Crusts (PDF, 250KB)
Soil Structure and Macropores (PDF, 480KB)

Chemical Properties

...topics coming soon

Biological Properties

Earthworms (PDF, 485KB)
Respiration (PDF, 329KB)

...more topics coming soon

For more information go to: