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ARS Home » Research » Publications at this Location » Publication #62629
Title: SOIL ORGANIC CARBON AND NITROGEN

Author
item Sikora, Lawrence
item Stott, Diane

Submitted to: Soil Science Society of America Special Publication Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 1/13/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The deterioration of productive soils in Africa motivated the United Nations to recommend programs that investigate the quality of present-day soils and determine how changes in practices have affected their present and future use. Soil organic matter has long been considered the key factor for judging soil quality. Measurement of the organic carbon and nitrogen portion in soil organic matter determines accurately the concentration of soil organic matter. However, several methods for measuring organic C or N are available. The purpose of this chapter is to recommend a method for analysis based on availability of the test to the most people, accuracy, safety, ease of interpretation and over-all costs. After reviewing several methods, the automated carbon and nitrogen analysis by dry combustion is recommended. Recommendations on sampling and preparing the soil for analyses are included. Although important, measurement of soil organic matter cannot alone determine soil quality.

Technical Abstract: Soil organic matter (SOM) has long been considered the key quality factor of soil. Soil organic matter is a source of and a sink for plant nutrients and is important in maintaining soil tilth, aiding air and water infiltration, promoting water retention, reducing erosion, and controlling pesticide efficacy and fate (Gregorich et al., 1993). If a land manager had the ability to make only two measurements to determine the quality of the soil, a crude estimate might be the determination of the organic C and N content. The recommended method for accurate determination of both organic C and N is the automated dry combustion method which detects C and N directly. This method should be available in each state, either at the state testing labs or at a commercial lab at a moderate price. The loss-on-ignition determination for organic C is recommended as an alternate low technology, moderate cost method. The wet chemical oxidation nmethods, such as the Walkley-Black or Kjeldahl, are less costly in materials, but is higher in labor costs, requires knowledge of analytical chemistry techniques, and uses hazardous chemicals that pose safety and waste disposal problems. Because SOM is a key to defining quality but does not singly provide sufficient information, measurement must be made in light of other quality indicators.