110. While off-setting anthropogenic emissions, C sequestration in terrestrial ecosystems has numerous co-benefits through enhancement of ecosystem services (Figure 15). Important among these are numerous benefits including increase in NPP with attendant improvement in production of food, feed, fuel, fiber and other materials of industrial importance (e.g., timber). Increase in the terrestrial C pool also buffers ecosystems against drastic perturbations through moderation of climate as influenced by atmospheric chemistry, erosive events and non-point source pollution and sedimentation, desertification control, denaturing and filtering of pollutants and improving water quality. There are also numerous supporting services such as increase in biodiversity, maintenance of landscape, improvement in land quality, and enhancement of cultural and aesthetical values of the land. Increase in ecosystem C pool contributes to production of goods and services of value to humans. Ecosystem indicators, which can be used to assess ecosystem health (Dale and Polasky, 2007) depend on the ecosystem C pool. Monteil (2008) reported that dust travelling from the Sahel across the Atlantic affects human health in the Caribbean. Hence adoption of SLM practices in the Sahel, with an attendant improvement in soil quality and productivity, can reduce the incidence of “Harmattan” and also provide local and global environmental benefits.
111. Improvement in watershed conditions via SLM is a key ingredient to reducing soil erosion, sedimentation, and non-point source pollution while enhancing water quality and C sequestration in terrestrial ecosystems. Sediment-bound nutrient transport, a principal cause of non-point source pollution, can be mitigated through simple SLM techniques of watershed management such as installation of microdam catchments used in Northern Ethiopia (Haregeweyn et al., 2008). Desertification and transport of dust to South America (McConnell et al., 2007) are linked to poor watershed management. Increasing drought severity, such as linked to Amazonian deforestation (Cox et al., 2008), can also be mitigated through adoption of SLM on a watershed scale. Nutrients transported by rivers for long distances (Subramaniam et al., 2008) are principal causes of eutrophication of coastal waters and strong indicators of poor land management practices in watersheds. Disposal of untreated municipal/urban waste, an important issue in developing countries, especially in large urban centers of South America (Mendez et al., 2008) is an integral component of watershed management. Thus, adoption of SLM options increases C sequestration, enhances watershed resilience, and improves the environment.
112. Havstad et al. (2007) identified 5 key elements of landscape dynamics: soils geomorphic characteristics, resource redistribution, transport of matter and water, environmental component, and historical legacies. Such landscape multi-functionality and natural capital are also related to SLM and ecosystem C pool. The multi-functionality of the landscape implies provision of a large number of goods and functions relating to social, economic and environmental prosperity and sustainability (Crossman and Bryan, 2009). Another important issue of SLM is that related to the natural capital. It is defined as the stock of assets provided by natural systems and the benefits that flow especially to humans (Costanza et al., 1997). There exists a strong inter-relationship between SLM for ecosystem C enhancement and the natural capital through strong linkage between environmental, economic and social factors. Both concepts of multi-functionality and natural capital can be linked through ecosystem C pool and SLM. An optimal ecosystem C pool is essential for the landscape to be multi-functional and have a high stock of natural capital. Increase in biodiversity is an example of multi-functionality of a landscape, because there exists spatial consequences between biodiversity and ecosystem services (Egoh et al., 2009).
113. Adoption of SLM is essential to soil quality and improvement in ecosystem C pool. Soil quality is defined as the “degree of fitness of a soil for specific use” –its ability or capacity to function for a specific purpose (Doran and Jones, 1996; Gregorich and Carter, 1997). Maintaining the natural resource base and soil quality through improvement in SOC is essential to achieving SLM (Lal, 1997). Rotations and cropping systems which return large quantities of biomass into the landscape generally improve soil quality (Hulugalle and Scott, 2008). Indeed soil quality is an ideal indication of SLM (Herrick, 2000).
XIX. Deepening and Scaling Up of SLM-Related C Sequestration Activities
114. Until the 1990s, the principal objectives of managing SOM in agricultural production systems were those related to improving soil fertility for increasing agronomic productivity. Therefore, SOM (SOC) concentrations and temporal changes were measured in the plow layer or the zone where roots of seasonal crops are concentrated. In this regard, SLM included cropping systems (rotations, sequences, combination, agroforestry measures), tillage methods (NT, reduced tillage, conservation tillage), surface cover (residue mulching, cover cropping), and nutrient management (compost, manure, biological N fixation, mycorrhizae, fertilizer) options which enhanced and sustained SOC concentration in the root zone. The latter has been measured in the units of percentage or weight basis (g/kg, mg/kg). With growing interest since 1990s in using soils as a sink for atmospheric CO2, SOM enhancement has acquired multi-functional considerations. As a C sink, soil depth of interest is 1-2 m rather that just the root zone. The labile SOC fractions and their dynamics (mineralization to release plant nutrients) are important to plant growth and agronomic productivity. In contrast, recalcitrant fractions and their permanence (long residence time without leakage) are important to addressing CC. Rather than the narrow interest in the plot-scale data to manage soil fertility using precision farming for crop production, it is the changes in the SOC pool at the watershed, regional or national scale which are relevant to off-setting anthropogenic emissions for mitigating CC. Thus, appropriate units of measurement are kg/ha, kg/ha/yr, Gt C/yr, etc. In addition to adoption of SLM options at farm scale, the goal is to accrue benefits by adoption at regional, watershed or national scale. It is important, therefore to scale up SLM options to regional and national scales for C sequestration. The need for upscaling of C sequestration activities, however, necessitates understanding and improving: (i) the process of SCS in relation to soil quality, (ii) methods for assessment of soil C at landscape scale in a cost-effective and credible manner, and (iii) predicting soil C pool at different scales. Indeed, improving soil quality through increase in SOC pool is an appropriate adaptation-mitigation win-win strategy, because it affects one of the largest terms of the global C balance through exchange of C between soils and the atmosphere (Gardi and Sconosciuto, 2007) while enhancing food/fiber production. Successful synergetic adaptation-mitigation SLM strategies are those which improve local livelihoods and strengthen resilience of target communities while making soils/ecosystem a net sink for atmospheric CO2 (Cerri et al., 2007a, b; Mauere et al., 2008).
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