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United States Department of Agriculture

Agricultural Research Service

Title: Assessing Soil Quality by Testing Organic Matter

Authors
item Sikora, Lawrence
item Cambardella, Cynthia
item Yakovchenko, Vladimir - OICD
item Doran, John

Submitted to: Soil Science Society of America Special Publication Book Chapter
Publication Type: Proceedings
Publication Acceptance Date: July 1, 1995
Publication Date: N/A

Interpretive Summary: The United Nations is concerned about the declining quality of soils in the world and stresses the need to determine quality and the effects of practices on soil quality. Most gardeners and farmers admit that a key to successful production of crops is adequate soil organic matter. Therefore, an indicator of increased quality of soil would be an increase of organic matter or decreased organic matter in the case of declining quality. Tota soil organic matter concentration changes very slowly, however, in response to changes in practices and therefore is not a good "early warning" signal. There are fractions of organic matter that change more quickly in response to change in practice. These fractions can be classified generally as "biologically active" fractions. The question, however, is how to interpret the changes in these fractions and their relationship to changes in total soil organic matter. Research is underway to answer this question.

Technical Abstract: Organic matter influences most soil properties and as such is the single most important indicator of soil quality. Loss of organic matter is considered detrimental to soil quality which is defined as the capacity of a soil to function within ecosystem boundaries, to sustain biological productivity, maintain environmental quality, and promote plant and animal health (Doran and Parkin, 1994). Soil organic matter (SOM) consists of different components such as living organisms, slightly altered plant and animal organic residues, and well-decomposed organic residues which vary considerably in their stability and susceptibility of further decomposition. Change in total SOM is slow in most instances and, therefore, may not be a good indicator of soil quality over short time periods of less than 5 to 10 years. Therefore measurement of the most labile and dynamic SOM fractions may provide more useful information and serve as 'early warning' indicators of the long-term effects of management on SOM and soil quality. Examples given include particulate organic matter, microbial biomass, and specific respiration which is defined as units of CO2-C per unit biomass C per unit of time. These SOM components respond more quickly to changes in management and soil treatment. However, consensus on the interpretation of these changes as they affect soil quality has not been reached.

Last Modified: 10/24/2014
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