On a global scale, soils contain 1500 Pg (Pg = 1015 g) C and 300 Pg N, compared with around 600 Pg C and 13 Pg N in terrestrial biomass, and 720 Pg C in the atmosphere (Chapter 2, this volume). Other important elements have similar relationships (Reeburgh, 1997). Another way to describe these relationships is that 1 m2 of normal Swedish arable topsoil (0-30 cm) with 4% organic matter (OM) contains 400 kg mineral soil, 8 kg C in soil organic matter (SOM) and 0.1 kg C in roots, whereas the atmosphere above this 1m2 contains 1.4 kg C (Andren et at, 1990). Since the pool of C in the atmosphere is considerably smaller than the pool of C in the soil, a small relative change in the amount of C in the soil will have a substantial influence on the C content in the atmosphere. Thus, understanding the processes regulating the dynamics of SOM and how they respond to a changing environment is crucial for managing our natural resources, and for understanding how the state of SOM may feed back to the change in climate. Other recent relevant reviews of this topic can be found in Bouwman (1990), Anderson (1992) and Lal et at. (1995).

Guide to Alternative Fuels

Guide to Alternative Fuels

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