Agriculture Reference
In-Depth Information
5
Soil Organic Matter Dynamics
Controls and Management for
Sustainable Ecosystem Functioning
Eldor A. Paul, Alexandra Kravchenko,
A. Stuart Grandy, and Sherri Morris
The composition of soil, particularly its organic matter content, reflects its role as a
major controller of ecosystem functioning and soil fertility (Paul and Collins 1998,
Basso et  al. 2011, Bhardwaj et  al. 2011). Soil organic matter (SOM), the largest
global reservoir of terrestrial organic carbon (C), contains three to four times as
much stored C as either the atmosphere or plant biomass. The soil biota, consisting
of microorganisms as well as fauna, account for 1-3% of total soil C and complete
the terrestrial C cycle by mineralizing SOM to carbon dioxide (CO 2 ) (Paul and
Collins 1998, Robertson and Paul 2000). Soil organic matter is a complex, multi-
structured, multicomponent pool of organic materials including decomposing plant
residues, associated microorganisms and their products, and a biochemically trans-
formed fraction, sometimes called humic material, that is complex in structure and
often associated with soil minerals. Microbially derived C, because of its unique
chemical structure and intimate association with minerals, is selectively protected
and represents a particularly important component of total SOM. This pool serves
as a dynamic source of labile nutrients and contributes to soil aggregate formation
and erosion resistance (Robertson and Paul 1998, Grandy and Neff 2008).
The investigation of SOM dynamics provides a wealth of information on how
organisms, including vegetation and soil biota, interact with climate, parent mate-
rial, landscape, and management over time to influence ecosystem functioning
(Collins et  al. 1997). One of the most promising approaches for understanding
SOM dynamics uses long-term incubations, together with tracers and density frac-
tionation, to interpret SOM pools and their turnover.
The multiple components that make up SOM can be divided into three pools
based on their turnover times (Paul et al. 2001a, b). The most labile, active pool is
104
Search WWH ::




Custom Search