ABSTRACT
Organic carbon (C) must be among the most commonly analyzed soil constituents, starting with
the earliest soil investigations. Already in the nineteenth century, chemists were routinely
analyzing soil C (e.g., Lawes and Gilbert 1885). Initially, these analyses were done to investi-
gate pedogenesis and to assess soil productivity, both of which are closely linked to organic C
(Gregorich et al. 1997). But more recently, scientists have been analyzing soil organic C (SOC)
for another reason: to measure the net exchange of C between soil and atmosphere (Janzen
2005). Indeed, building reserves of SOC has been proposed as a way of slowing the rising
atmospheric CO2 concentrations caused by burning fossil fuel (Lal 2004a,b).
