Submitted to: Encyclopedia of Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: 9/4/2001
Publication Date: 12/10/2001
Citation: Franzluebbers, A.J. 2001. Soil ecology and the cycling of carbon and nitrogen in the soil environment. Encyclopedia of Soil Science. Interpretive Summary: This article is one of several contributions in the category Soil Ecology for the Encyclopedia of Soil Science. It summarizes the carbon and nitrogen cycles as they take place in soil. The contributions of soil fauna and soil microflora to carbon and nitrogen cycling are important for the efficient utilization of nutrients and protection of soil, water, and air quality. The major environmental factors that control soil organisms are temperature, soil water content, soil texture, and spatial distribution of organic substrates. Optimum temperature and water contents maximize soil organism activity, while deficiencies and excessive levels slow their activity. Soil organisms can be protected from predators inside aggregates formed in fine-textured soils. Organic substrates that determine soil microbial activity are most abundant near plant roots and at the soil surface, where plant residues are deposited. Plant residues with high carbon:nitrogen ratio lead to immobilization of nitrogen and can limit microbial biomass development. Finally, the mechanisms for loss of nitrogen from soil are described, including denitrification, volatilization, leaching, and runoff.
Technical Abstract: Carbon (C) and nitrogen (N) are two of the most important elements that affect the soil's productivity and environmental quality. Carbon is found throughout nature in a wide variety of forms and particularly in soil (i) as complex organic compounds derived from living organisms, (ii) as carbonate minerals such as calcite and dolomite, and (iii) as carbon dioxide and methane as decomposition endproducts. Nitrogen is an essential element of plants, animals, and microorganisms that is a part of chlorophyll, enzymes, amino acids, and proteins, which are necessary for growth and development of organisms. In soil, the quantity of N in organic matter and as clay-fixed ammonium far exceeds quantities in plant-available forms of nitrate and ammonium. Carbon and nitrogen occur in various forms and undergo transformations from one form to another, primarily through biochemical manipulations involving enzymes. The forms and fluxes of an element are commonly illustrated in a cycle following the principles of conservation of mass. Once in soil, the carbon cycle is dominated by the heterotrophic process of decomposition. Carbon and N transformations are carried out by a wide variety of organisms living in soil, which interact to form a food web.