Soil is the largest terrestrial pool of organic carbon, containing approximately 2344 gigatons of organic carbon globally. This is second only to the ocean. Of this carbon, 54% is stored in the top three metres of soil.
Ploughing soil can lead to an 11% reduction in soil organic matter (Smith, 2004), with a soil carbon loss of up to 50% into the atmospheric climate over a period of 50-100 years (Lehmann, 2006). This means that arable soils often have the lowest soil carbon of all land classes.