It is a critical task of scientists in these disciplines to employ their knowledge to develop methods for reducing the negative impacts of climate change on the soil resulting from climate change.
Deforestation, drainage of wetlands, and, in general, conversion of natural ecosystems to agricultural use have contributed over the last 250 years to about 30% of the total anthropogenic emissions of C to the atmosphere. Soil organic C (SOC) pool (2500 Pg) is the second largest global C pool after the oceanic pool (38,000 Pg), and it stocks more than three times the amount of atmospheric C (750 Pg) and about 5 times the C stored in living biomass. The SOC pool is relatively low in arid sandy soils (30 Mg ha -1 ) but generally ranges from 50 to 150 Mg ha -1 (Lal et al., 2004 ).
A large fraction of the CO 2 emitted from soil is derived directly from mineralization of stocked soil organic C (SOC) and can be attributed to agricultural management practices.
Dynamics of the SOC pool are not completely understood, yet they are key to understanding why accumulation of CO 2 in the atmosphere is actually proceeding at a much slower rate than predicted by models on the basis of fossil fuel burning and deforestation (IPCC, 2001). Estimates of the current net uptake of C by the terrestrial biosphere in the northern hemisphere have identifi ed the existence of a large (1 -2 Pg C yr -1 ) terrestrial C sink (IPCC, 2001;Nabuurs, 2004 ;Ciais et al., 1995 ). For North America and Europe, the terrestrial C sink has been estimated to amount, respectively, to 0.3 -0.6 Pg C yr -1 (Pacala et al., 2001 ) and 0.1 -0.2 Pg C yr -1 (Janssens et al., 2005 ). If Europe were to maintain its current forest and grassland sink and stop all C losses from arable and peat soils, the terrestrial SOC sink alone would absorb 16% of the European C emissions from fossil fuel consumption (Freibauer et al., 2004 ).
Soil organic matter (SOM) decomposition could also be the agent of a feedback mechanism that could further enhance the warming trend of the planet (Cox et al., 2000 ). Under a warmer climate, thawing of high -latitude permafrost regions may result in large releases of CO 2 to the atmosphere (Goulden et al., 1998 ;Oelke et al., 2004 ). Furthermore, changes to massive soil drainage due to permafrost melting may have a large impact on the C stored in high -latitude peatlands (Bubier et al., 2003 ;Lafl eur et al., 2003 ) and may signifi cantly contribute to the climate -carbon cycle feedback (Schimel et al., 1994 ).
The additional release of CO 2 from SOM mineralization from 1991 to 2051, calculated on the basis of a 0.003 ยฐ C yr -1 increase in temperature, amounts to 61 Pg C and is equivalent to 19% of that released from fossil fuel combustion assuming unabated use. It is therefore important to quantify precisely this contribution. Uncertainties in estimation of the contribution of this feedback mechanism depend on changes in the distribution pattern and intensity of precipitation, but also on the behavior of the more recalcitrant fractions of SOM (Jenkinson et al., 1991 ). Better knowledge of the factors that affect decomposition of organic matter (OM) in soil and eventually control rates at which different fractions decompose is urgently required and would be of immediate practical importance.
According to the U.N. Framework Convention on Climatic Change, total worldwide CO 2 emission amounts to 428,941 Gg yr -1 and the 10% reduction required by the Kyoto Protocol would correspond to 11,698 Gg C yr -1 . Lal (2002b) estimated the Soil texture Clay mineralogy Calcium content Determining factors