Assessment of Organic Carbon Status in Indian Soils - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 331

Table 28.2. Carbon stocks in the Indo-Gangetic
Plains, India, and other parts of the world (values
in Pg).

An increase in carbon stocks in soils under
continuous wetland rice has also been
reported (Bronson et al ., 1998; Sahrawat
et al ., 2005; Kukal and Rehana-Rasool
Benbi, 2008). A Global Environment Facil-
ity (GEF) financed project on the assessment
of SOC stocks and the change at the na-
tional scale in four countries including
India (Milne et al ., 2006) indicated an in-
crease in the SOC stock in the IGP by about
4.5% from 1990 to 2000, as per the Century
model, due mainly to the increase in prod-
uctivity in rice-based systems (Bhattacharyya
et al ., 2007c). SOC stocks in 2030 are
predicted to decline to the level of 1990
in the wake of presumed land management
changes in near elimination of the fallow-
rice system and doubling of the area under
triple-cropped rotations. An Intergovern-
mental Panel on Climate Change (IPCC)
model showed essentially no change in
SOC stocks from 1990 to 2030. Studies
carried out under the Global Environment
Facility Soil Organic Carbon (GEFSOC)
project and the National Agricultural Tech-
nology Project (NATP) on SOC for the IGP
and BSR regions have further strength-
ened the viewpoint that there is an im-
provement in the SOC of soils under the ex-
isting agricultural management practice
( Tables 28.3 and 28.4) . Continuation of the
same cropping pattern, therefore, rings no
alarm bells on the drop of SOC levels in the
IGP and the BSR in the near future, although
the increase in CaCO 3 in soils will remain a
concern (Bhattacharyya et al ., 2007b).

Soil depth (m)

Region 0-0.3 0-1.5

IGP, India a 0.63 2.00

India b 9.77 29.97

Tropical Regions c 201-213 616-640

World c 684-724 2376-2456 d

a Bhattacharyya et al ., 2004; b Bhattacharyya et al ., 2008;
c Batjes, 1996; d for 0-2.0 m soil depth.

The increasing trend of soil organic
matter over the past two
decades in India

Recent studies on SOC over a long period
indicate an increasing trend in both the
IGP (Benbi and Brar, 2009) and the BSR
(Bhattacharyya et al ., 2007b). The evalu-
ation of large soil test data for 25 years
(1981/ 82 to 2005/06) has shown improve-
ment in the SOC status under intensive
agriculture in Punjab. On average, the SOC
increased by 38% for the whole Punjab,
from 2.9 g kg - 1 in 1981/ 82 to 4 g kg - 1 in
2005/ 06. The increase in SOC content was
significantly related to the increase in R/W
performance. This increase was linear,
from 5.9 t ha - 1 in 1981/ 82 to 8.1 t ha - 1 in
1999/2000. The increased productivity of
R/W has resulted in an increased seques-
tration of carbon in the plough layer by
0.8 t C ha - 1 of increased grain production
(Benbi and Brar, 2009). The All India Co-
ordinated Research Project (AICRP) on
long-term fertilizer experiments (LTFEs)
showed that SOC contents were improved
over years under the recommended level
of fertilizer application (Biswas and Benbi,
1997; Manna et al ., 2006; Singh and
Wanjari, 2009). The increased sequestra-
tion of C in the R/W system under inten-
sive agriculture is due to improved crop
productivity, greater turnover of biomass
(both above ground and below ground),
greater transport of carbon into roots (rhizo-
sphere) and reduced organic matter decom-
position under anaerobic wetland rice.

Benefits of SOC for Crop Production
and Agroecosystem Functioning

SOC and its influence has been studied by
different models, namely Century, RothC
and InfoCrop, with the help of different
LTFEs. Many long-term fertilizer experi-
mental data sets have been documented for
the IGP and the BSR (Bhattacharyya et al .,
2007c, 2011, 2012). Besides, soil survey
data sets have also been used to find out
the benefits of SOC in different land-use
systems.