Importance of inorganic carbon in sequestering carbon in soils of the dry regions

Abstract

The world's most populated ecoregions in the tropics are also the regions where there is a high risk of natural resources and environmental degradation. The con-sequences of this degradation are severe soil degradation, contamination of sur-face and ground waters and emission of greenhouse gases from the soil into the atmosphere. Human activities, driven by socio-economic, political and cultural fac-tors that exacerbate gaseous emissions, include conversion of lands under forest and natural vegetation to agriculture and other uses, biomass burning, lack of nutrient inputs under subsistence agricul-ture and draining of wetlands 1 . Soils in the tropics, especially those in the drier regions have low reserves of organic matter and plant nutrients. The soil carbon (C) pool composed of soil orga-nic C and soil inorganic C is not only critical for the soil to perform its produc-tivity and environmental functions, but also plays an important role in the global C cycle. The sequestration of atmosphe-ric C in the soil and biomass not only redu-ces greenhouse effect but also helps maintain or restore the capacity of the soil to perform its production and envi-ronmental functions on a sustainable basis. Thus, there is a great interest in research on sequestration of atmospheric C into the soils for maintaining or restoring soil fertility and mitigating carbon dioxide emissions to the atmosphere 1 . Calcium carbonate is a common mineral in soils of the dry regions of the world, stretching from sub-humid to arid zones. It is estimated that arid and semi-arid regions cover over 50% of the total geo-graphical area of India. The soils of these regions are calcareous in nature. Accord-ing to an estimate by the National Bureau of Soil Survey and Land Use Planning, calcareous soils occupy about 230 × 10 6 ha and constitute 69% of the total geographical area of the country 2 . Some calcareous soils also occur in the humid and per-humid zones of the country, but the occurrence of calcareous soils in the per-humid zones is as a result of strongly calcareous parent material or in young geomorphic surfaces 3 . The arid and semi-arid regions of India are dominated by calcareous Vertisols and Vertic inter-grades. Despite the dominant role that calcium carbonate plays in modifying the physi-cal, chemical and biological properties and behaviour of plant nutrients in the soil, its role in C sequestration in cal-careous soils is not well researched. The role of soil inorganic carbon (SIC) is important for sequestering C, but the mechanisms involved are not well under-stood 1 . The soils of the arid and semi-arid regions may contain two to five times more SIC than soil organic C (SOC) in the top 1 m soil layer. For example, Bhattacharya et al. 4 estimated that the SOC stock in the top 150 cm depth of the black cotton soils (Vertisols and asso-ciated soils) of Maharashtra is 171 Gg (Gg = 10 9 g) and the stock of SIC is 3051 Gg. These estimates clearly demon-strate the predominance of SIC over SOC. The SIC pool consists of primary inor-ganic carbonates or lithogenic inorganic carbonates, and secondary inorganic car-bonates or pedogenic inorganic carbo-nates. Secondary carbonates are formed through dissolution of primary carbo-nates and re-precipitation of weathering products. The reaction of atmospheric carbon dioxide (CO 2) with water (H 2 O) and calcium (Ca 2+) and magnesium (Mg 2+) in the upper horizons of the soil, leaching into the subsoil and subsequent re-precipitation results in formation of secondary carbonates and in the seque-stration of atmospheric CO 2 . The reac-tions can be represented as follows: CO 2 (g) + H 2 O = H 2 CO 3 , (1)

Full text

CORRESPONDENCE
CURRENT SCIENCE, VOL. 84, NO. 7, 10 APRIL 2003 864
Importance of inorganic carbon in sequestering carbon in soils of the
dry regions
The world’s most populated ecoregions
in the tropics are also the regions where
there is a high risk of natural resources
and environmental degradation. The con-
sequences of this degradation are severe
soil degradation, contamination of sur-
face and ground waters and emission of
greenhouse gases from the soil into the
atmosphere. Human activities, driven by
socio-economic, political and cultural fac-
tors that exacerbate gaseous emissions,
include conversion of lands under forest
and natural vegetation to agriculture and
other uses, biomass burning, lack of
nutrient inputs under subsistence agricul-
ture and draining of wetlands1.
Soils in the tropics, especially those in
the drier regions have low reserves of
organic matter and plant nutrients. The soil
carbon (C) pool composed of soil orga-
nic C and soil inorganic C is not only
critical for the soil to perform its produc-
tivity and environmental functions, but
also plays an important role in the global
C cycle. The sequestration of atmosphe-
ric C in the soil and biomass not only redu-
ces greenhouse effect but also helps
maintain or restore the capacity of the
soil to perform its production and envi-
ronmental functions on a sustainable basis.
Thus, there is a great interest in research
on sequestration of atmospheric C into
the soils for maintaining or restoring soil
fertility and mitigating carbon dioxide
emissions to the atmosphere1.
Calcium carbonate is a common mineral
in soils of the dry regions of the world,
stretching from sub-humid to arid zones.
It is estimated that arid and semi-arid
regions cover over 50% of the total geo-
graphical area of India. The soils of these
regions are calcareous in nature. Accord-
ing to an estimate by the National Bureau
of Soil Survey and Land Use Planning,
calcareous soils occupy about 230 ×
106 ha and constitute 69% of the total
geographical area of the country2. Some
calcareous soils also occur in the humid
and per-humid zones of the country, but
the occurrence of calcareous soils in the
per-humid zones is as a result of strongly
calcareous parent material or in young
geomorphic surfaces3. The arid and semi-
arid regions of India are dominated by
calcareous Vertisols and Vertic inter-
grades.
Despite the dominant role that calcium
carbonate plays in modifying the physi-
cal, chemical and biological properties
and behaviour of plant nutrients in the
soil, its role in C sequestration in cal-
careous soils is not well researched. The
role of soil inorganic carbon (SIC) is
important for sequestering C, but the
mechanisms involved are not well under-
stood1. The soils of the arid and semi-
arid regions may contain two to five times
more SIC than soil organic C (SOC) in
the top 1 m soil layer. For example,
Bhattacharya et al.4 estimated that the
SOC stock in the top 150 cm depth of
the black cotton soils (Vertisols and asso-
ciated soils) of Maharashtra is 171 Gg
(Gg = 109 g) and the stock of SIC is
3051 Gg. These estimates clearly demon-
strate the predominance of SIC over SOC.
The SIC pool consists of primary inor-
ganic carbonates or lithogenic inorganic
carbonates, and secondary inorganic car-
bonates or pedogenic inorganic carbo-
nates. Secondary carbonates are formed
through dissolution of primary carbo-
nates and re-precipitation of weathering
products. The reaction of atmospheric
carbon dioxide (CO2) with water (H2O)
and calcium (Ca2+) and magnesium
(Mg2+) in the upper horizons of the soil,
leaching into the subsoil and subsequent
re-precipitation results in formation of
secondary carbonates and in the seque-
stration of atmospheric CO2. The reac-
tions can be represented as follows:
CO2 (g) + H2O = H2 CO3, (1)
H2CO3 = H+ + HCO3– , (2)
CaCO3 + H+ = Ca2+ + HCO3– . (3)
The overall reaction that leads to the
dissolution of calcium carbonate at the
soil surface, followed by its leaching in
the soil profile, is as follows:
CO2 + H2O + CaCO3 = Ca2+
+ 2HCO3– . (4)
The pedogenic inorganic C (PIC) formed
from non-carbonate material is a sink for
C and leads to C sequestration. On the
other hand, pedogenic inorganic C formed
from calcareous material may not be
involved in C sequestration in the soil.
Thus dissolution of carbonates and lea-
ching in the soil profile may lead to C
sequestration. Leaching of bicarbonates
into the groundwater is a major mecha-
nism of SIC sequestration. The rate of C
sequestration by this mechanism may be
0.25–1.0 Mg C/ha/yr5. For SIC seques-
tration to take place, the groundwater is
to be unsaturated with calcium bicarbo-
nate6. The contribution of PIC from non-
carbonate material may be 50–100 kg/ha/
year6.
Enhanced primary productivity of the
vegetation and adoption of salinity con-
trol measures involving the use of gyp-
sum and organic amendments can lead to
leaching of calcium bicarbonate in the
profile under irrigation. This would result
in sequestering carbon and amelioration
of salt-affected soils7. Unlike SOC, the
role of SIC in C sequestration is not only
less researched, but also less well under-
stood. Sequestration of SIC certainly has
implications when groundwaters unsatu-
rated with calcium bicarbonate are used
for irrigation. Reconstruction of carbo-
nate fluxes in soil formed in strongly
calcareous parent material over geological
time periods suggests that this mecha-
nism could account for upward of 1 Mg
ha–1 yr–1 of SIC8. These results provide
definitive estimates of contribution that
SIC can make to C sequestration in cal-
careous soils.
It has been postulated that aridity in
the climate is responsible for the forma-
tion of pedogenic calcium bicarbonate and
this is a reverse process to the enhance-
ment in SOC. Thus increase in C seque-
stration via SOC enhancement in the soil
would induce dissolution of native calcium
carbonate and its leaching4, resulting in
SIC sequestration. Thus there may be a
synergy in SOC and SIC sequestration.
Initial estimates on SIC sequestration in
soils should stimulate future research on
its role in C sequestration for enhancing
C stock in impoverished and degraded
calcareous soils in the arid and semi-arid
regions and mitigating the greenhouse
effect.
1. Lal, R., Adv. Agron., 2002, 76, 1–30.
2. Velayutham, M., Mandal, D. K., Mandal,
C. and Sehgal, J. L., National Bureau of

CORRESPONDENCE
CURRENT SCIENCE, VOL. 84, NO. 7, 10 APRIL 2003 865
Soil Survey and Land Use Planning Bulle-
tin No. 35, NBSS and LUP, Nagpur,
1999.
3. Pal, D. K., Dasog, S., Vadivelu, S., Ahuja,
R. L. and Bhattacharya, T., in Global Cli-
mate Change and Pedogenic Carbontes (eds
Lal, R. et al.), CRC/Lewis Publishers,
Boca Raton, Florida, 2000, pp. 149–185.
4. Bhattacharya, T., Pal, D. K., Velayutham,
M., Chandran, P. and Mandal, C., Clay Res.,
2001, 20, 11–20.
5. Wilding, L. P., in Carbon Sequestration in
Soils: Science, Monitoring and Beyond
(eds Rosenberg, N. J. et al.), Battelle Press,
Columbus, 1999, pp. 146–149.
6. Nordt, L. C., Wilding, L. P. and Drees,
L. R., in Global Climate Change and
Pedogenic Carbonates (eds Lal, R. et al.),
CRC/Lewis Publishers, Boca Raton,
Florida, 2000, pp. 43–64.
7. Gupta, R. K. and Abrol, I. P., in Advances
in Soil Science: Soil Degradation (eds Lal,
R. and Stewart, B. A.), Springer-Verlag,
Berlin, 1990, pp. 223–288.
8. Izaurralde, R. C., Rosenberg, N. J. and
Lal, R., Adv. Agron., 2001, 70, 1–75.
K. L. SAHRAWAT
International Crops Research Institute
for the Semi-Arid Tropics,
Patancheru 502 324, India
e-mail: klsahrawat@yahoo.com
NEWS
INDEST Consortium
In a major initiative under the Department
of Secondary and Higher Education, Mini-
stry of Human Resource and Development
(MHRD), an Indian National Digital
Library in Science and Technology
(INDEST) has been set up. With the
launch of INDEST, in the initial phase,
at least 38 major technological institu-
tions in the country such as the IITs,
IISc, NITs, RECs and IIITs are slated to
benefit. The doors are now open for new
consortia members, as the whole concept
is open-ended. INDEST serves to benefit
members by ‘shared subscription’ through
a consortium of libraries. The sharing of
resources at highly discounted rates of
subscription hopes to increase access to
e-journals, etc. for researchers across the
country, while obtaining better terms of
agreement with publishers. The consor-
tium’s web address is http://www.library.
iitb.ac.in/indest/. The aim, according to
INDEST, is to improve ‘quality and quan-
tity of research’.
Presently, science and technology insti-
tution libraries bear about Rs 4 crores as
expenses for subscription towards jour-
nals etc. This costs the Government of
India approximately Rs 150 crores annu-
ally, to support library acquisitions all
over the country for centrally funded
institutions. INDEST could provide com-
parable or even better facilities of infor-
mation-sharing at Rs 18.6 crores, that is
the funding invested by the Government
of India per annum in the consortium.
The quantum of government support is
not likely to vary in future years, accord-
ing to Pawan Agarwal, MHRD.
Based on the recommendations of the
MHRD Task Force, institutions have been
grouped into three categories. Category I
comprises IISc, Bangalore and the seven
IITs. Category II, all the RECs/NITs;
Indian School of Mines, Dhanbad; North
Eastern Regional Institute of Science
and Technology, Itanagar, and the Sant
Longowal Institute of Engineering and
Technology, Chandigarh: Category III
comprises six IIMs (Ahmedabad, Banga-
lore, Kolkata, Indore, Kozhikode, Luck-
now); the National Institute of Training
in Industrial Engineering, Mumbai, and
the Indian Institute of Information Tech-
nology and Management, Gwalior. Few
additional members have recently joined
Category III, such as the Dhirubhai
Ambani Institute of Information and
Communication Technology, Gandhi-
nagar; TIFR Laboratory of Computa-
tional Mathematics, Pune; Birla Institute
of Technology, Ranchi; Nirma Institute
of Technology, Ahmedabad, and SONET,
Hyderabad. AICTE has set-up a commit-
tee to find out the possibility of AICTE-
accredited institutions joining the
consortium.
The electronic resources available
through INDEST are the following:
Full-text electronic resources:
• IEEE/IEE Electronic Library
(http://ieeexplore.ieee.org)
• Elsevier: Science Direct
(http://www.sciencedirect.com)
• Springer Verlag’s link
(http://link.springer.de/)
• ProQuest: Applied Science and Tech-
nology Plus
(http://www.il.proquest.com/pqdauto/)
• ProQuest: ABI/Inform Complete
(http://www.il.proquest.com/pqdauto/)
• ACM Digital Library
(http://portal.acm.org/portal.cfm)
Online Databases:
• Ei Compendex Plus and INSPEC
(http://www.engineeringvillage2.org/)
• SciFinder Scholar (Access through a
Z39.50 Windows-based interface)
• MathSciNet
(http://www.ams.org.mathscient)
• ISI Web of Science
(http://isiknowledge.com/)
• J-Gate Custom Content for Consortia
(http://www.informindia.co.in).
Belonging to a particular category deter-
mines type of access, as usability and
suitability of various electronic resources
have been the criteria for selection to a
particular category.
On 4 March 2003, the first annual meet-
ing of INDEST consortium was held at
IIT Delhi. According to Pawan Agarwal,
the resources of management, civil and
mechanical engineering institutions were
not adequately covered, although the
Task Force had identified such resources.
He spoke of the issues involved that con-
fronted INDEST, such as funding, sele-
ction of resources, spreading the benefits
to all institutions, collaborative working,
shifting to an electronic work environ-
ment, training of users, copyright issues
and lack of networking.
Further, mention must be made of
efforts currently on by several agencies
to form their own ‘Nets’, such as UGC,
CSIR, ICAR, etc., outside of the INDEST
consortium. The MHRD hoped that there
would be no duplication of efforts and
such dissenting voices would eventually