Anthropogenic perturbation of the global carbon cycle has increased the atmospheric concentration of carbon dioxide, and decreased the carbon pool in the world's agricultural soils. Since the industrial revolution, the atmospheric concentration of carbon dioxide has increased by about 30% from 280 parts per million by volume (ppmv) to 370 ppmv. This increase is attributed to emissions of carbon from fossil fuel combustion estimated at 270 Pg (gigatons), and from land use change and soil cultivation estimated at 136 Pg. Conversion of natural to agricultural ecosystems, with attendant soil erosion and rapid mineralization of soil organic matter, has depleted the carbon pool by 66 to 90 Pg for global soils, and 3 to 5 Pg for soils in the United States. Depletion of the soil organic carbon pool has adverse impacts on soil quality leading to increase in risks of soil erosion, decline in aggregation and soil structure, reduction in plant available water capacity, decline in activity and species diversity of soil fauna, and overall decline in agronomic/biomass productivity. The decline in soil quality is more severe in soils of the tropics than temperate regions, and in soils managed for low-input subsistence farming than those under intensive commercial agriculture. Soils of Sub-Saharan Africa, Central and South Asia, and tropical
America are severely depleted of their organic matter pool, prone to degradation by erosion and other processes, do not respond to inputs, and have low productivity.
The world population of 6.06 billion in 2000 will increase to 7.2 billion in 2012, 8.3 billion in 2030, and 9.3 billion in 2050. Practically all the increase in the world population will occur in the developing countries, where soils are severely depleted of their organic carbon pool and have low productivity. The population of developing countries will increase by 35% from 4.9 billion in 2000 to 6.6 billion in 2025. The required increase in cereal production by 2025 will be 778 million MT, an average of 31 million MT per year. The required increase in 2050 will be 1519 million MT, an average of 30 million MT per year. The required cereal production in developing countries will be more than double by 2050, mainly because of the projected rapid increase in population. The increase in food production will have to come from increasing production per unit area from existing land, because there is little if any potential for bringing new land under cultivation. Therefore, restoring the quality of degraded soils is essential, for which enhancing soil organic carbon pool is a principal prerequisite.
Restoring the depleted organic carbon pool in soils of developing countries of the tropics and subtropics is a challenging task for several reasons. First, the resource poor farmers may not be able to afford the inputs needed to attain the required increase in crop yield even if the inputs were made available. Second, crop residues and other bio-solids that must be returned to the soil are invariably used for other purposes, such as household fuel, fodder, fencing and construction material, and so on. Third, the decomposition rate of organic matter may be four to five times higher in the tropics than in temperate climates. Thus, there is a need to develop appropriate farming systems to cater to the multifaceted demands of the resource-poor small landholders of the tropics.
Encouraging adoption of recommended management practices for enhancing the organic carbon pool is not a simple task for the soils of temperate climates of the developed economies either. There is a strong need to provide incentives and commodify soil carbon, which can then be traded like any other farm commodity. While the Clean Development Mechanism (CDM) under the Kyoto Protocol and the BioCarbon Fund of the World Bank may be policy tools for providing incentives to farmers of developing countries, international emissions trading joint implementation, among others, may be useful tools for those in developed countries.
This book addresses six complex and interactive themes as follows:
1. The impact of projected climate change on soil quality, water resources, temperature regime, and growing season duration on net primary productivity of different biomes
2. Soil carbon dynamics under changing climate
3. The impact of changes in carbon dioxide and ecological environments on agronomic yields and food production in various world regions
4. World food demands and supply during the 21st century
5. Policy and economic issues related to carbon trading and enhancing agricultural production
6. Research and development priorities for enhancing soil carbon pool and food security.
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