Basic Principles of Soil Carbon Management for Multiple Ecosystem Benefits - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 269

(Six et al ., 2000; Barthes et al ., 2008). The
arrangement of stable aggregates defines the
soil pore volume and size distribution,
which in turn affects most soil properties
related to water and gas transport (Horn
and Smucker, 2005). Many studies have
shown that soils under permanent pastures
have better structure than agricultural soils
that are tilled frequently (Pulleman and
Marinissen, 2004; Zach et al ., 2006; Noelle-
meyer et al ., 2008; Berhongaray et al .,
2013). This is one way in which crop rota-
tions that include grass fallows contribute
to soil structure maintenance. No-till (NT)
agriculture (see Chapter 23, this volume)
also has been shown to improve soil struc-
ture when compared to traditional ploughed
cultivation systems through reducing soil
disturbance (Six et al ., 2002b; Smith and
Bolton, 2003; Hollinger et al ., 2005; Zo-
tarelli et al ., 2005; Lorenz et al ., 2006; Lal
et al ., 2007; Quiroga et al ., 2009; Fernández
et al ., 2010; López et al ., 2012). However, C
input into a soil is also a major factor in sta-
bilizing soil structure and soil C (Kong and
Six, 2010). Therefore NT combined with
other agricultural practices that enhance C
input such as mulching (Rockström et al .,
2009) and planting of cover crops will fur-
ther stabilize soil structure and increase
soil C (Ding et al ., 2006; Alletto et al ., 2011;
dos Santos et al ., 2011; Restovich et al .,
2012; Zhu et al ., 2012).

and therefore is affected strongly by SOM
dynamics. SOM content is an important fac-
tor determining aggregate stability (Cerda,
2000; Eynard et al ., 2004), and the dry ag-
gregate size fraction (<0.84 mm) can be used
as an indicator of the susceptibility of soils
to wind erosion (Zobeck et al ., 2003; López
et al ., 2007). A shift from conventional cul-
tivation to conservation tillage systems can
reduce water (Schuller et al ., 2007) and
wind erosion drastically (Hevia et al ., 2007).
This beneficial effect of conservation tillage
has been related to higher SOM contents
and greater surface porosity under conser-
vation till (Kirkby et al ., 2000; Rhoton and
Shipitalo, 2002). Another factor contribut-
ing to erosion control is the permanent soil
cover provided by living or dead plants
under conservation tillage (López et al .,
2003; Soane et al ., 2011) or natural vegeta-
tion systems (Adema et al ., 2004). Repeated
ploughing to a fixed depth can lead to sub-
surface soil compaction and the formation
of plough layers (Hamza and Anderson,
2005), which reduce water infiltration and
hence increase erosion (Zink et al ., 2011).
Rotational and integrated cropping systems
that promote subsurface root development
can mitigate the effect of repeated plough-
ing (Keller et al ., 2012). In rangelands or
pastures, grazing intensity is an important
driver of erosion; overgrazing promotes ero-
sion (Oztas, 2003) by compacting the soil's
surface layer (Franzluebbers and Stuede-
mann, 2008; Steffens et al ., 2008; Barto
et al ., 2010) and reducing above- and below-
ground C inputs.

Soil carbon management
for erosion control

The loss of mineral and organic soil par-
ticles through water and wind erosion cause
an irreversible loss of resources that sustain
soil-based ecosystem services. In some cases,
erosional processes transport both organic
matter and clay particles short distances, and
result in a spatial redistribution of these
elements (Polyakov and Lal, 2004; Li et al .,
2008a,b): in many cases, however, the
eroded particles are transported much
greater distances and lost from productive
lands (Ballantine et al ., 2005). The preven-
tion of soil erosion depends largely on the
stability of soil structure (Fattet et al ., 2011)

Soil management for climate
regulation

Soil C stocks are determined by inherent
soil properties such as clay content and
type, as well as climate, vegetation and land
use (Swift, 2001; Noellemeyer et al ., 2006;
Gili et al ., 2010). Soils have a finite quantity
of C they can store, and the potential for C
sequestration in a given area will be greatest
for degraded soils with C contents well
below their saturation level (Six et al .,