This manuscript reviews the potential impact of residue management, conservation tillage and soil restoration on carbon sequestration in world soils. The greenhouse effect is among four principal ecological issues of global concern that include: (i) adequacy of land resources to meet needs of present and future generations; (ii) role of world soils and agricultural practices in the "greenhouse" effect; (iii) potential of crop residue management, restoration of degraded soils, and conservation tillage in carbon sequestration in soil; and (iv) minimizing risks of soil degradation by enhancing soil resilience and soil quality. Annual increase in CO, concentration in the atmosphere is 3.2 X 1015 g, and there exists a potential to mitigate this effect through C sequestration in soils. Just as world soils are an important active pool of organic carbon and play a major role in the global carbon cycle, crop residue is a major renewable resource which also has an important impact on the global carbon cycle. I have estimated the annual production of crop residue to be about 3.4 billion Mg in the world. If 15% of C contained in the residue can be converted to passive soil organic carbon (SOC) fraction, it may lead to C sequestration at the rate of 0.2 X 1015 g/yr. Similarly restoring presently degraded soils, estimated at about 2.0 billion ha, and increasing SOC content by 0.01%/yr may lead C sequestration at the rate of 3.0 Pg C/yr. Conservation tillage is an important tool for crop residue management, restoration of degraded soil, and for enhancing C sequestration in soil. Conservation tillage, any tillage system that maintains at least 30% of the soil surface covered by residue, was practised in 1995 on about 40 X 106 ha or 35.5% of planted area in USA. It is projected that by the year 2020, conservation tillage may be adopted on 75% of cropland in USA (140 X 106 ha), 50% in other developed countries (225 X 106 ha), and 25% in developing countries (172 X 106 ha). The projected conversion of conventional to conservation tillage may lead to a global C sequestration by 2020 at a low estimate of 1.5 X 1015 g, and at a high estimate of 4.9 X 1015 g of C. These potentials of C sequestration can be realized through adoption of regional, national and global soil policy that stipulate appropriate use of world soil resources.
