Assessment of Organic Carbon Status in Indian Soils - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 334

Identifying systems for organic C
sequestration

The maximum threshold limit of SOC is
2.42%, which corresponds to a minimum
threshold limit of BD (1.22 Mg m -3 ). This is
the maximum SOC obtained in the forest
ecosystem in SAT, India.

SOC, SIC (soil inorganic carbon) and TC
(total carbon) stocks were estimated while
identifying systems for carbon sequestration
in the semi-arid tropics (SAT) in India. The
database generated was used to identify sys-
tems keeping in view the fact that effective
carbon management can help not only in
building the SOC stock to a level of 10.5 Pg,
from their existing level of 2.5 Pg, but also in
reducing the SIC stock to the tune of 1.9 Pg,
much to the benefit of growing plants in
terms of the better physical and chemical
environment of soils (Bhattacharyya et al .,
2006b). In SAT, benchmark spots of agricul-
ture and horticulture were identified as suit-
able management under two distinctly dif-
ferent conditions ( Fig. 28.1) . The minimum
threshold limit of SOC is 0.63% (0-30 cm
soil depth), which is associated with a max-
imum threshold value of bulk density (BD)
(1.6 Mg m -3 ). These threshold limits were
arrived at since they (of SOC and BD) corres-
pond to approximately 10 Pg SOC stock in
India (0-30 cm soil depth) (Bhattacharyya
et al ., 2000). These minimum SOC and max-
imum BD values correspond to an average
value of 1.19% SIC. The minimum thresh-
old value of SOC may, therefore, increase
SIC and BD effecting poor soil drainage.

Century model experience

LTFE data sets were used to evaluate the
performance of the Century ecosystem model
in contrasting ecoregions of India, viz. Mohanpur
(humid) and Akola (semi-arid), with a mean
annual rainfall of 1619 mm and 793 mm, re-
spectively. At the humid site, the modelled
data simulated the measured data reason-
ably well for all the treatments, with control
and treatments with fertilizer alone and in
combination with organic inputs. Century
modelled changes in SOC more success-
fully at Mohanpur than at Akola. The SOC
levels were low to start with at Mohanpur
and gradually showed an increasing trend
when external inputs (fertilizers and ma-
nures) were added. Century closely predicted
the SOC levels measured at Mohanpur for
all the treatments. In Akola, measured SOC
exhibited a sharp increase when both inor-
ganics and organics were added in combin-
ation or organics applied separately. At the
semi-arid site, Century performed well for
the early years and less well during the end

Conditions

Minimum threshold of SOC (0.63%)
Maximum threshold of BD (1.6 Mg m -3 )

Maximum threshold of SOC (2.42%)
Minimum threshold of BD (1.22 Mg m -3 )

Corresponds to ~ 10 Pg SOC stock in 0-30 cm soil
depth in India

Fig. 28.1. Conditions of identifying systems for organic carbon sequestration in soils of SAT, India.
(From Bhattacharyya et al ., 2006b.)