Carbon Sink Capacity and Agronomic Productivity of Soils of Semiarid Regions of India - Principles of Sustainable Soil Management in Agroecosystems - page 445

The term “soil carbon sequestration” implies transferring atmospheric CO 2 into
long-lived pools and storing it securely so that it is not immediately remitted. Thus,
soil C sequestration means increasing SOC and SIC stocks through judicious land
and crop management practices (Lal 2004) (Table 16.9). The potential soil C sink
capacity of managed ecosystems approximately equals the cumulative historic C loss
estimated at 55 to 78 Pg (1 Pg = 10 9 Mg = 10 15 g). The attainable soil C sink capacity
is only 50% to 66% of the potential capacity. Atmospheric CO 2 is one of the principal
GHGs, and its concentration has been steadily increasing from 280 µmol mol -1 in
1750 to about 370 µmol mol -1 by 2000 (+32%) and 390 µmol mol -1 by 2010 (+39%).
The atmospheric CO 2 is currently increasing at the rate of 0.5% per year (3.4 Pg C
year -1 ).
The development of agriculture during the last two centuries and particularly
since the 1990s has entailed depletion of SOC stocks. World soils are among the
planet's largest reservoirs of C and hold potential for expanded C sequestration, and
thus provide a prospective way of mitigating the increasing atmospheric concentra-
tion of CO 2 . The United Nation Convention to Combating Desertification (UNCCD)
is concerned that extensive areas of formerly productive land, in the arid and semi-
arid regions in particular, have been rendered unsuitable for crop production due
to land degradation. Land degradation not only reduces crop yields but also often
reduces the C content of agroecosystems, which is of concern in the context of global
warming.

TABLE 16.9
Comparison between Traditional Methods and RMPs in Relation to SOC
Sequestration
Traditional Methods RMPs

1. Biomass burning and residue removal Residue returned as surface mulch

2. CT and clean cultivation Conservation tillage, NT, and mulch farming

3. Bare/idle fallow Growing cover crops during the off-season

4. Continuous monoculture Crop rotations with high diversity

5. Low-input subsistence farming and soil
fertility mining

Judicious use of off-farm input

6. Intensive use of chemical fertilizers INM with compost, biosolids, and nutrient

cycling; precision farming

7. Intensive cropping Integrating trees and livestock with crop

production

8. Surface flood irrigation Drip irrigation, furrow irrigation, or

subirrigation

9. Indiscriminate use of pesticides Integrated pest management

10. Cultivating marginal soils Conservation, restoration of degraded soils

through land use change

Source: Lal, R., Geoderma , 123, 1-22, 2004.