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| Soil provides food. |
Soil quality is defined in various ways. Implicit in most definitions of soil quality is the idea that the most important attributes of a healthy soil vary, depending upon a human value judgment about the primary function of a particular soil in a specific location.
Many define soil quality in terms of a soil's ability to perform its basic functions. These functions include a soil's role in plant growth, hydrology (i.e., the Water Cycle), biological transformations, and degradation of organic materials. All four of these functions are important in both agricultural and ecological contexts.
Soil quality is frequently defined as: "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" (USDA - Natural Resources Conservation Service, Soil Science Society of America).
Soil quality may also be defined simply as "fitness for use." Although soil has many functions and uses, this bulletin focuses on the use of soils for production of vegetable and small fruit crops. In this context, farmers often define a soil's quality based on its ability to produce a good crop with minimal inputs.
Evaluation of soils for agricultural and other land uses has been practiced for generations. In modern times, extensive soil surveys completed in the United States and elsewhere classified the suitability of soils for agricultural and other uses. However, classifying soils based on their intrinsic (and, mostly, unalterable) properties is not the same as evaluating soil quality.
Soil quality is not concerned with rating or comparing the suitability of different soil types for a specific use, such as agriculture. Instead, soil quality is concerned with evaluating the condition of a particular soil in relation to its potential capacity. Therefore, the focus of soil quality is on properties or processes impacted by soil management. In considering soil quality, do not ask "Is this soil suitable for farming?" Rather, ask "How will my management affect this soil?"