The soil carbon (C) stock, comprising soil organic C (SOC) and soil inorganic C
(SIC) and being the largest reservoir of the terrestrial biosphere, is a critical part
of the global C cycle. Soil has been a source of greenhouse gases (GHGs) since
the dawn of settled agriculture about 10 millenia ago. Soils of agricultural ecosystems
are depleted of their SOC stocks and the magnitude of depletion is
greater in those prone to accelerated erosion by water and wind and other
degradation processes. Adoption of judicious land use and science-based
management practices can lead to re-carbonization of depleted soils and
make them a sink for atmospheric C. Soils in humid climates have potential
to increase storage of SOC and those in arid and semiarid climates have potential
to store both SOC and SIC. Payments to land managers for sequestration of
C in soil, based on credible measurement of changes in soil C stocks at farm
or landscape levels, are also important for promoting adoption of recommended
land use and management practices. In conjunction with a rapid
and aggressive reduction in GHG emissions across all sectors of the economy,
sequestration of C in soil (and vegetation) can be an important negative
emissions method for limiting global warming to 1.5 or 2°C