The carbon budget in soils

The global soil C reservoir, similar to 1500 Gt of C (1 Gt = 10(12) kg of C ), is dynamic on decadal time scales and is sensitive to climate and human disturbance. At present, as a result of land use, soil C is a source of atm ospheric CO2 in the tropics and possibly part of a sink in northern latitud es. Here I review the processes responsible for maintaining the global soil C reservoir and what is known about how it responds to direct and indirect human perturbations. "I am fire and air; my other elements I give to baser life" -William Shakespeare, Antony and Cleopatra.