27. The SLM options and related ecological actions can be prioritized on the basis of principal land uses. These land uses are chosen on the basis of their agronomic/economic significance to advancing food security for the growing population, and also their sensitivity to be affected by and/or affect the projected CC. Therefore, this report focuses on four land uses deemed important to SLM for mitigation of and adaptation to CC. These are: (i) tropical forest ecosystems, (ii) savannas, grasslands and rangelands, (iii) croplands, and (iv) degraded and desertified soils including salinized soils. Relevant SLM options for these three land uses are outlined in Figure 9. The SLM strategy outlined in Figure 9 is part of a farming system approach that presents an innovative way of exploiting the land resources in rural and periurban areas in ways that maintain the integrity of the land while enhancing the livelihood of the producers. The value of SLM options listed in Figure 9 can be enhanced to accentuate both local and global benefits by harnessing their potential to sequester C in soils and biota, and accrue other co-benefits.
28. Priority action strategies listed in Figure 9 are based on the following criteria: (i) wherever possible, avoid deforestation and conversion of other natural ecosystems (e.g., savannahs, cerrado, pampas, llanos, steppes, peatlands) to agricultural land use, (ii) intensify agricultural production on existing crop lands, (iii) increase use efficiency of inputs by enhancing production per unit input of fertilizer, irrigation water and other energy-based components of farming systems, (iv) take marginal lands out of production and convert these to restorative/perennial land use (e.g., tree crops, afforestation), (v) provide incentives to resource-poor farmers in developing countries through payment for ecosystem services rather than subsidies or emergency handouts, and (vi) commodify C sequestered in the soil by developing transparent mechanisms for trading such C credits.
IX. Operationally Relevant SLM Technologies and Practices for Diverse Soils and Land Uses
29. To be relevant and effective, SLM technology must meet certain key criteria:
(i) Technology must be scientifically proven through reliable and data-driven information, repeatable and measureable results, soil-specific agronomic yields, and objectivity-based conclusions. In addition, the choice of SLM technology must be based on local validation through participatory on-farm research.
(ii) The benefits (agronomic and economic) must be concrete, highly visible, and substantial and must accrue directly to the local producers. In situations where crop yields are extremely low (1 t/ha in rainfed farming in SSA, and SA), a technology which increases yield by 10 to 15% may not be sufficient. In view of the increasing population and rising food demand, SLM technology may need to triple or quadruple crop yields over a short period of 5 to 10 years. Therefore, productivity, efficiency, cost-effectiveness, and profitability are important considerations.
(iii) The SLM technology must be ecologically compatible, especially with regards to the current and projected CC. Important ecological factors are drought stress, unfavorable temperatures, high incidence of pests and pathogens, and increase in risks of erosion and other extreme events.
(iv) The SLM technologies must be socially acceptable and ethically grounded. The severe problem of soil degradation can be reversed by creating awareness about the stewardship of land resources. Faith-based and cultural organizations must be involved to teach responsibility, respect, generational/gender/social equity, fairness, and societal values of natural resources through SLM.
(v) Political support and acceptibility is extremely important to any SLM technology and strategy. The Green Revolution largely by-passed SSA partly due to lack of political support. It is now taking root in some countries of SSA (e.g., Malawi, Ghana) maily because of political support. Visionary leadership, committed to national progress and economic growth (rather than personal), is essential to relevance and effectiveness of SLM options.
(vi) SLM adaptation technologies must be considered as an integral component of the mitigation options. These should be considered neither as policy alternatives, nor as opposite to mitigation. In addition, SLM technologies that have appreciable mitigation benefits should be given the prominence they deserve, relative to other industrial mitigation technologies (e.g., clean coal, CCS).
(vii) There must by a minimal of trade-offs in terms of competition for land, water, nutrients, energy, etc. SLM technologies requiring additional inputs, are essential to advancing food security, restoring ecosystesm services, and improving the environment. In comparison, forest plantations would require additional water, nutrients and lands. Increasing food crop productivity through SLM is potentially important to limiting atmospheric CO2 concentrations (Wise et al., 2009). In view of these considerations, SLM technologies for four prominent ecoregions are described in the following sections.
X. Tropical Forest Ecosystems (TFEs)
30. Forest land uses are important buffers against sudden environmental (e.g., climate) change. Indeed, geographical ranges of tree species have expanded and contracted several times since the last glacial epoch (Hamrick, 2004). Yet, the impact of change of TFEs on the environment and vice versa is an important factor in identifying appriopriate SLM strategies. The large land area and high biodiversity of TFEs warrant a detailed examination of their importance in the global C cycle. Tropical forests store 40-50% of C in terrestrial vegetation (Lewis et al., 2009). The TFEs occur within the humid tropics or the bioclimates characterized by consistently high temperatures and high relative humidity. Total annual rainfall of these regions ranges from 1500 mm to 4500 mm received over 8-12 months. The TFE biome occupies a total area of 1.8 billion hectares (Bha); the vegetation of the humid tropics is dominated by rainforest, covering 1.1 Bha to 1.5 Bha, or about 30% of the land area within the tropics (Table 3). But the available estimates of area of TFE vary widely. For example, Bruenig (1996) estimated the area of rainforest at 1.64 Bha in 1985 and 1.5 Bha in 1995. Knowledge about the major soil types and their distribution is essential to understanding soil-related constraints and making a rational choice of the appropriate SLM options.The available information indicates that the predominant soils of these ecoregions are Oxisols, Ultisols, Alfisols, and Inceptisols. Of the total land area of TFEs of 1.8 Bha, 35% are Oxisols, 28% are Ultisols, 15% are Inceptisols, 14% are Entisols, 4% are Alfisols, 2% are Histosols, and 2% comprises Spodosols, Mollisols, Vertisols and Andisols (NRC, 1993). Soil-related constraints to crop production include nutrient imbalance characterized by low availability of N, P, Ca and Mg; low pH, and toxic concentrations of Al and Mn. Rather than attaining the steady state condition of the ecosystem C budget, even mature TFEs are natural C sinks because of the recovery of landscapes following disturbances (e.g., storms, fire, wind damage). Lugo and Brown (1992) estimated that TFEs removed from the atmosphere 2.0 to 3.8 Gt C/yr during 1980s.
Table 3. Estimates of area under tropical rainforest (Adapted from NRC, 1993; FAO, 2003).
|
Region
|
Tropical Rainforest Area (Mha)
|
1980
|
1990
|
2000
|
Africa
|
289.7
|
241.8
|
224.8
|
Latin America
|
825.9
|
753.0
|
718.8
|
Asia
|
334.5
|
287.5
|
187.0
|
Total
|
1450.1
|
1282.3
|
1130.6
|
31. Conversion of natural TFEs to agricultural land use leads to a rapid decline in the SOC pool which, in severely degraded soils, may decrease to 20% of the antecedent pool (Figure 10). Adoption of recommended SLM practices and technologies on degraded soils of TFEs can help sequester more SOC (mitigation) and adapt to CC. These practices include: no-till (NT) cropping of root or grain crops with crop residue mulch and integrated nutrient management (INM) for soil fertility improvement, adoption of agroforestry measures, establishing tree crop plantations (cocoa, coffee) with companion shade crops, and afforestation with rapidly growing and site-adapted plantations (Lal, 2005a, b). The rate of SOC sequestration under these SLM strategies depends on the amount and quality (C:N ratio, lignin content, etc.) of biomass added, depth and proliferation of the root system, conservation-effectiveness of these measures for erosion control and change in soil moisture and temperature regimes that decreases the rate of decomposition of the biomass. The key is to select SLM practices that increase biomass addition to the soil, decrease the rate of its decomposition, and create a positive ecosystem C budget. Restoration of degraded soils and agriculturally marginal lands through afforestation and establishment of perennial vegetation cover (plantations) is an important strategy. Afforestation is also important for water conservation and reducing risks of soil erosion and sedimentation. Establishment of deep-rooted species helps transfer biomass C into the sub-soil where it is away from the zone of frequent perturbations (e.g. farm operations, erosion), and is sequestered for a long time.
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