Assessment of Organic Carbon Status in Indian Soils - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 340

The reported emissions due to enteric
fermentation and rice cultivation were
6.59 Tg C-CH 4 year - 1 and 3.07 Tg C-CH 4 year - 1 ,
respectively (NATCOM, 2004). The aver-
age emission coefficient derived from all
categories weighted for the Indian rice
crop was 74.05 ± 43.28 kg ha - 1 (Manjunath
et al ., 2011). The total mean emission from
the rice lands of India was computed as
2.54 Tg C-CH 4 year - 1 . Methane from Indian
agricultural soils is only 0.23% of the global
warming caused by the world's CO 2 emis-
sion (Bhatia et al ., 2004).

the SIC:nitrogen ratio is relatively narrow
in lowland rice-rice systems, which indi-
cates that the pedo environment in rice soils
keeps the deteriorating effect of CaCO 3 for-
mation and the concomitant sodicity at
bay. Pedogenic CaCO 3 formation has been
linked with the development of soil sodici-
ty. This sodicity causes chemical soil deg-
radation, indicating poor content of SOC.
Pan et al . (1997) indicated that both SOC
and SIC were equally important for C trans-
fer and potential CO 2 sequestration. They
found a negative correlation between SOC
and SIC in arid ecoregions of China. It is
now known that, with the adversity of the
climate, there will be depletion of organic
carbon and C will be sequestered as CaCO 3
in the soils (Pan and Guo, 2000; Bhattacha-
ryya et al ., 2004). Despite this, the system
of intensive agriculture in the IGP and the
BSR has increased the SOC stock. In spite
of the formation of CaCO 3 in the soils, the
SOC increase suggests that the prevailing
agricultural land uses have been able to
enhance or maintain the level of organic
carbon in the soils of these two food pro-
duction zones of the country. Despite the
fact that the increase in CaCO 3 is a bane
for farmers, the increase in SOC has al-
ways been possible due to the adoption
of suggested management interventions,
even in arid and semi-arid environments.
However, the rise in CaCO 3 ( Tables 28.3
and 28.4) warrants a fine-tuning of the
existing management interventions. Until
then, the status of inorganic C in soils
will remain a warning signal for potential
soil degradation (Bhattacharyya et al .,
2007b).

General Observations

Out of the two important food-growing
regions, the IGP has contributed largely to
high levels of crop production compared
to the BSR. It was observed that during
the post-Green Revolution era, cropping
intensity in the dominant states of the IGP
increased from 137% (1976/77) to 158%
(1999/2000). During the same period, the
BSR remained less intensively cultivated,
with an increase in cropping intensity from
111% to 123%. Despite this difference,
SOC stock of both the soils has increased
from 1980 to 2005. However, the increase
was more in the IGP than in the BSR. This
was due to more biomass turnover to the
soils, as evidenced from the increased SOC
in the fertilized areas of a long-term experi-
ment ( 30 years) in the IGP. In addition, an
exercise through the GEFSOC modelling
system also projected an increase in SOC
stock using the LTFE data sets of the IGP.
SOC stocks in the BSR indicated an in-
crease, albeit more in the double-cropped
areas and also in areas where green ma-
nuring was practised, indicating that the
prevailing agricultural land uses helped
in sequestering more organic carbon in soils
of both these regions. The mechanisms in-
volved in preferential accumulation of or-
ganic matter in wetland soils under paddy
may be ascribed mainly to anaerobiosis
and the associated chemical and biochem-
ical changes that take place in submerged
soils. It has recently been reported that

Acknowledgements

The present work is a compilation of find-
ings of different projects funded by the
Global Environment Facility (GEF), the
Department of Science and Technology
(DST), India, the National Agricultural
Technology Project (NATP) and the Indian
Council of Agricultural Research (ICAR),
New Delhi, India.