Agricultural activities and the global carbon cycle

The observed and projected increase in emission of greenhouse gases, with attendant effects on global warming and sea level rise, have raised interests in identifying mitigation options. Terrestrial C sequestration involves capture of atmospheric C through photosynthesis and storage in biota, soil and wetlands. Land use, vegetation and soil management have a strong impact on the biotic processes of C sequestration. Losses of C from the terrestrial ecosystems are exacerbated by deforestation, biomass burning, plowing, resource-based and subsistence agriculture, and practices that mine soil fertility and deplete the soil organic C (SOC) pool. Biomass burning may also produce charcoal, which is an inert carbon with long residence time. Practices that enhance C sequestration include afforestation and reforestation, conservation tillage and mulch farming, integrated nutrient management and adopting systems with high biodiversity. Net C sequestration within an ecosystem can be assessed by taking into account the hidden C costs of fertilizers, pesticides, tillage, irrigation and other input. Restoration of degraded soils and ecosystems has a vast potential of C sequestration. The Kyoto Protocol provides for C sequestration in terrestrial sinks and C trading through Clean Development Mechanisms. Terrestrial C sequestration, besides being a win–win strategy, offers a window of opportunity for the first few decades of the 21st century. It is a natural process of reducing the rates of gaseous emissions while alternatives to fossil fuel take effect.