Sollins, Phillip; Glassman, Carol; Paul, Eldor A.; Swanston, Christopher; Lajtha, Kate; Heil, Justin W.; Elliott, Edward T. 1999. Soil carbon and nitrogen: pools and fractions. In: Robertson, G. Philip; Coleman, David C.; Bledsoe, Caroline S.; Sollins, Phillip, eds. Standard soil methods for long-term ecological research. New York, NY: Oxford University Press: 89-105.
Soil organic matter (SOM) is important as a major source of most nutrients, especially nitrogen (the one major plant nutrient not supplied by weathering), and as a source of cation exchange capacity, especially in highly weathered soils. SOM also contributes to good soil structure, thus promoting drainage, water-holding capacity, aeration, and root penetration, and provides strong control of soil pH, especially in highly weathered soils. In addition, soil organic matter is amajor global C source and sink. Jenkinson et al. (1991) calculated that an increase in global temperature of 0.03 °C/yr could increase CO2 release from soil by about 1 Gt C/yr over the next 60 years; by comparison, fossil fuel burning currently releases about 5 Gt C/yr.
Soil nitrogen availability limits plant growth in many terrestrial ecosystems, yet increased N deposition due to atmospheric pollution has been implicated in the decline of forest productivity in some heavily industrialized parts of the northern temperate zone (Schulze 1989). The relation between total soil N and nitrogen availability to plants is still unclear, in large part because the nature of soil organic N is only now beginning to be understood.
In this chapter we present standard methods for determination of total soil C and N and measurement of total organic and inorganic soil C. Methods are also presented for separating SOM into biologically meaningful fractions. Field sampling methods and soil standards are discussed in Chapter 2, this volume.