25. The term ‘C sequestration’ implies capture and secure storage of atmospheric CO2 into other pools such as biotic, pedologic/soil (together called terrestrial), geologic and oceanic so that it is not re-emitted into the atmosphere. In comparison, SCS occurs through humification of biomass and its stabilization through physical, chemical and biological processes. These processes are described briefly in this report along with techniques for measurement and modeling of the SOC pool for the purpose of trading soil C credits. The strategy of C sequestration is important because: (i) there are not yet viable non-C fuel sources, (ii) there is a strong need to stabilize atmospheric abundance of CO2, (iii) it is essential to restore and enhance ecosystem services through restoration of degraded/desertified soils by increasing the SOC pool, and (iv) it is essential to harness the numerous advantages of SCS over the engineering techniques of C capture and storage (CCS) into geologic/oceanic strata. The important point is that most SLM technologies and practices for SCS are proven and in use in many parts of the world. However, what is lacking is the adoption of these practices at scale. On the other hand, technologies such as carbon capture and storage show promise but are yet to be fully proven and applied widely. But there is no time to lose in dealing with the CC challenge: urgency is the key in reducing accumulation of C in the atmosphere. And the SLM practices presented in this report can be put to immediate use for SCS in a cost-effective manner. In addition to being cost-effective, other benefits of SCS include: (i) improvements in soil quality and agronomic/biomass productivity, (ii) increase in use efficiency of inputs such as fertilizer, irrigation water, energy, (iii) decrease in erosion and non-point source pollution, (iv) reduction in risks of hypoxia in coastal ecosystems, (v) increase in soil biodiversity, (vi) improvement in agronomic production, and (vii) achievement of local, regional and global food security. Despite numerous advantages, there are several concerns of SCS which must also be addressed through SLM options. These are: (i) low soil C sink capacity of 20 to 30 t/ha which can be filled at a modest rate of 0.3 to 1.0 t/ha/yr, (ii) uncertainties about the permanence of SCS which depends on land use, soil management and land tenure, and (iii) need for simple and routine methods of estimating changes in soil C pool for a landscape, region or watershed over a short period of 1 to 2 years. Significant advances have been made since the 1990s in effectively addressing some of these concerns. Land use, land use change, and conversion of degraded/desertified lands to restorative use are important to enhancing the ecosystem C pool. The choice of appropriate SLM practices is important to realizing the economic/technical potential for C sequestration of an ecosystem, because land use is an important means to alter the NPP of a terrestrial ecosystem. SCS is a readily implementable option for both mitigation and adaptation to CC, and it can be undertaken in most parts of the world and at different scales. It is important to point out that in addition to benefits of adaptation, SCS can also provide mitigation comparable in cost to current abatement options in other industries (Bangsund and Leistritz, 2008).
VII. SLM Technologies and Other Greenhouse Gases
26. In addition to CO2, emissions of methane (CH4) and nitrous oxide (N2O) are also influenced by SLM. While CO2 accounts for 63% of the total radiative forcing by long-lived GHGs (WMO, 2008), SLM technologies also play an important role in mitigation of and adaptation to the effects of other GHGs. The data in Table 2 show increase in atmospheric abundance of 3 GHGs due to anthropogenic activities. Methane contributes 18.5% of the direct radiative forcing. Principal sources of CH4 are wetlands, termites, ruminants, rice paddies, fossil fuel exploitation, biomass burning and landfills. Nitrous oxide contributes 6.2% of the total radiative forcing. Principal sources of N2O are oceans, soils, biomass burning, fertilizer use and fossil fuel combustion. Various SLM practices have a positive impact on reducing atmospheric abundance of all three GHGs. Good soil structure, through CA/NT and other mulch farming oxidizes atmospheric CH4 and makes soil a sink. Improving use efficiency of nitrogenous fertilizers reduces N2O emission. The data on CH4 and N2O emission can be converted into CO2 equivalent by multiplication with the appropriate GWP value of 25 and 298, respectively.
Table 2. Atmospheric abundance and radiative forcing of three greenhouse gases (Adapted from WMO, 2007; IPCC, 2007).
