Carbon and the 'carbon cycle'. Over the past century, CO2 levels have risen significantly. There is considerable debate about the reasons -- whether it's a natural cycle or the result of increased CO2 emissions due to human activities-- but there is general agreement that human activity accounts for part of the increase, especially in view of the continuing increase of CO2 levels following the on-set of the industrial age. There is a great amount of research regarding the benefits of organic matter or soil carbon in improving soil quality and the sustainability of balanced agriculture productivity.
Available at: http://works.bepress.com/mark_hanna/98/