Soil Quality Information Sheet 

Soil Quality - Introduction 

USDA Natural Resources Conservation Service Revised June 2001 

What is soil? 

Soil is a dynamic resource that supports plant life. It is 

made up of different sized mineral particles (sand, silt, 

and clay), organic matter, and numerous species of 

living organisms. Thus, soil has biological, chemical, 

and physical properties, some of which are dynamic and 

can change in response to how the soil is managed. 

What does soil do for us? 

Soil provides several essential services or functions: 

Soil supports the growth and diversity of plants and 

animals by providing a physical, chemical, and 

biological environment for the exchange of water, 

nutrients, energy and air. 

Soil regulates the distribution of rain or irrigation water 

between infiltration and runoff, and regulates the flow 

and storage of water and solutes, including nitrogen, 

phosphorus, pesticides, and other nutrients and 

compounds dissolved in the water. 

Soil stores, moderates the release of, and cycles plant 

nutrients and other elements. 

Soil acts as a filter to protect the quality of water, air, 

and other resources. 

Soil supports structures and protects archeological 

treasures. 

What is soil quality? 

Soil quality is the capacity of a specific kind of soil to 

function, 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. Changes in the capacity of 

soil to function are reflected in soil properties that 

change in response to management or climate. 

Why is soil quality important? 

Management that enhances soil quality will benefit 

cropland, rangeland, and woodland productivity. 

Enhanced soil quality can help to reduce the onsite and 

offsite costs of soil erosion, improve water and nutrient 

use efficiencies, and ensure that the resource is 

sustained for future use. It also benefits water quality, 

air quality, and wildlife habitat. 
How is soil quality evaluated? 

Soil quality is evaluated separately for each individual 

soil using soil quality indicators that reflect changes in 

the capacity of the soil to function. Useful indicators are 

those that are sensitive to change, and change in 

response to management. The type and number of 

indicators used depends on the scale of the evaluation 

(i.e., field, farm, watershed, or region) and the soil 

functions of interest. For example, infiltration rate and 

aggregate stability help indicate the capacity of the soil 

to intake water and resist runoff and erosion. Changes in 

soil organic matter, including active organic carbon or 

particulate soil organic matter, may indicate changes in 

productivity. Increased bulk density may reflect limits to 

root growth, seedling emergence, and water infiltration. 

Measurements of indicators can be made with simple to 

somewhat complex field tests, or sophisticated 

laboratory analyses. 

To evaluate soil quality, indicators can be assessed at 

one point in time or monitored over time to establish 

trends. 

An assessment provides information about the current 

functional status or quality of the soil. The assessment 

must start with an understanding of the standard, 

baseline value, or reference value to be used for 

comparison. Assessments can be made to help identify

areas where problems occur, to identify areas of special 

interest, or to compare fields under different 

management systems. Land managers can use this 

information, along with data from soil surveys, fertility

tests, and other resource inventory and monitoring data, 

to make management decisions. 

Monitoring of soil quality indicators over time 

identifies changes or trends in the functional status or 

quality of the soil. Monitoring can be used to determine 

the success of management practices or the need for 

additional management changes or adjustments.

What concerns relate to soil quality? 

Evaluating soil quality can improve the response to 

many resource concerns, including those listed below. 

For further information, refer to other Soil Quality

Information Sheets. 

• Loss of soil by erosion 

• Deposition of sediment by wind or floodwaters 

• Compaction of layers near the surface 

• Degradation of soil aggregates or soil structure 

• Reduced infiltration and increased runoff 

• Crusting of the soil surface 

• Nutrient loss or imbalance 

• Pesticide carryover 

• Buildup of salts 

• An unfavorable change in pH 

• Loss of organic matter 

• Reduced biological activity 

• Poor residue breakdown 

• Infestation by weeds or pathogens 

• Excessive wetness 

• Increased water-repellency of soils due to fire 

• Reduced water quality 

• Greenhouse gas emissions 

The full series of Soil Quality Information Sheets is available at http://soils.usda.gov/sqi. 

This Sheet was prepared by the Soil Quality Institute in cooperation with the National Soil Survey Center, NRCS, USDA; 

and the National Soil Tilth Laboratory, Agricultural Research Service, USDA 

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