Soil Carbon Transition Curves: Reversal of Land Degradation through Management of Soil Organic Matter for Multiple Benefits - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 35

Arable and rangeland soils in semi-arid
environments are vulnerable to wind ero-
sion (Hevia et al ., 2007; Li et al ., 2008) and
can exhibit compaction and other physical
problems (Hamza and Anderson, 2005; Cas-
tellano and Valone, 2007), leading to dimin-
ished productivity and higher risk of crop
failure (Stage II). Within this context, intrin-
sic soil properties, such as texture and min-
eralogy, and environmental conditions (spe-
cifically climate) affect the resilience or
buffer capacity of soils to mitigate the deg-
radation processes triggered by Stage I land
use. Soils with high clay contents in semi-
arid tropics sequester more soil organic car-
bon (Bhattacharyya et al ., 2000, 2006), and
therefore might be better buffered against
the impacts of declining soil organic car-
bon, whereas sandy soils, even in temperate
climates, will degrade more rapidly and
are more prone to collapse (Noellemeyer
et al ., 2006).

many experimental sites, was also evalu-
ated by a modelling exercise (Bhattacharyya
et al ., 2007a).
Changes in soil organic carbon stocks
of paddy soils in China indicate that the
total stock of carbon stored in the upper
30 cm of soils increased from 2.51 Pg in
1980 to 2.65 Pg in 2008, with an average se-
questration rate of 5.0 Tg carbon per year
(Xu et al ., 2012). This notable increase of
soil organic carbon stocks occurred mainly
between 1980 and 1994, and was associated
with an increase in chemical fertilizer ap-
plications. After 1994, the level of soil or-
ganic carbon stocked in the soil became
relatively stable, with only a slight upward
trend observed, although the use of chem-
ical fertilizer still increased (Xu et al ., 2012).
In central Argentina, the introduction
of no-till agriculture facilitated agricultural
management for carbon accrual (Alvarez
and Steinbach, 2009). Even when plant res-
idues were partially removed by grazing,
no-till soil maintained and recovered soil
organic matter (Quiroga et al ., 2009).
Adequate grazing management can
also reverse the degradation process and
lead to a stabilization or even accumulation
of soil organic carbon. This is done mainly
through rotational grazing schemes that
allow plant debris to be accumulated on the
soil (Savory and Butterfield, 1998; Hooker
and Stark, 2008) or through revegetation
strategies (Jiao et al ., 2011). Higher net pri-
mary productivity achieved through fertil-
ization and improved arable and pasture
crops contributes to higher residue returns
and a more positive carbon budget (Hole-
plass et al ., 2004).
In vast regions of agricultural land
around the world, no-till agriculture was
introduced which facilitated the accumula-
tion of soil organic carbon in arable soils
(Alvarez and Steinbach, 2009; Chapter 23,
this volume). Nevertheless different land-use
types condition the amount of soil organic
carbon they can possibly attain, and consid-
erably lower soil organic carbon contents are
typical for cash crop production in inten-
sive arable agriculture as compared to, for
example, animal husbandry systems in exten-
sive grasslands (Berhongaray et al ., 2013).

Stage III: On the road to recovery

After decades of decline, Minasny et al .
(2011) documented an increase in soil car-
bon in agricultural lands across the island
of Java, Indonesia, in the past two decades.
They attributed this to the effects of soil
conservation plus increased intensity of
cropping, which resulted in higher root in-
puts to the soil.
Table 3.3 shows the changes in carbon
stock of the selected benchmark locations in
the Indo-Gangetic Plains of India in 1980
and 2005, reflecting a positive response to
improved methods of cultivation. In gen-
eral, the increase in soil organic carbon
stock was higher in semi-arid and subhu-
mid dry portions of the Indo-Gangetic Plains.
Carbon stock changes in the soils of selected
benchmark spots in the black soil region
due to intensive agriculture are also evi-
dent, but the relative increase of soil organic
carbon is larger in the Indo-Gangetic Plains
than in the black soil region (Bhattacharyya
et al ., 2008). The application of fertilizer
and a combination of fertilizer and farm-
yard manure has increased the soil organic
carbon stock. This observation, found in