Soil Carbon and Nitrogen Pools and Fractions

Abstract 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 a major 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.