117. The SOC turnover and agronomic productivity are strongly influenced by climatic factors and a range of environmental variables. Therefore, several models have been developed to assess SOC sequestration under different land uses and management scenarios. Two widely used SOC prediction models are CENTURY 4.0 (Parton et al., 1987; 1988) and Roth C-26.3 (Coleman and Jenkinson, 1995; Jenkinson and Rayner, 1977). These models have been extensively used to assess the effects of modifying agricultural practices to increase soil C pool in Africa and Latin America (Farage et al. 2007), in the Brazilian Amazon region (Cerri et al., 2007) and Asia. Traore et al. (2008) used Roth C 26.3 in subhumid West Africa to estimate the SOC pool for community level C contracts. The Soil and Terrain (SOTER) model (FAO et al., 2007) is based on land resource information system in which each map unit represents a unique, relatively uniform combination of landform/terrain, parent material and soil characteristics (Van Engelen and Wen, 1995). Batjes (2008) mapped SOC pool in Central Africa using SOTER. The Global Environment Facility (GEF) co-financed a project to develop and demonstrate a system for producing spatially explicit estimates of SOC pool and changes at the national and sub-national scales. This project used Century, Roth C, and other models to develop the GEFSOC Modeling System (Milne et al., 2007). The model has been used to estimate SOC pool in the Brazilian Amazon, the Indo-Gangetic Plains of India, and for Kenya and Jordan (Falloon et al., 2007).
118. A bottom-up modeling approach can also be useful in assessing the regional C budgets using field data. Pascala et al. (2001) estimated the C budget in the U.S. using a variety of inventory data on the basis of a bottom-up approach. Janssens et al. (2003) used top-down and bottom-up approaches to estimate Europe's current C sink capacity. There are numerous uncertainties in such estimates because of the complex nature of C uptake and heterogeneity of land surfaces. Therefore, the net ecosystem carbon exchange (NEE) technique, a bottom-up approach, is used to measure the ecosystem C budget. This procedure is based on the flux measurements using micro-meteorological methods called FLUXNET (Baldocchi et al., 2001). Ito (2008) has applied the FLUXNET technique using AsiaFlux data to estimate the regional C budget of East Asia. Ratification of the Kyoto Protocol has indeed encouraged development of a range of modeling techniques to assess the potential of C sequestration in cultivated soils under different climate change scenarios. Using this technique, Lugo and Berti (2008) identified SLM practices for North-East Italy as follows: (i) conversion of cropland to grassland with sequestration rate of 2.5 to 13.8 t C/ha by the end of the first commitment period, and (ii) business as usual was a source of C by 20.8 t C/ha.
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