Soil Carbon Sequestration for Mitigation: How much can climate mitigation in agriculture rely on sequestering carbon in soils on existing, working agricultural lands?  My report with the World Resources Institute, World Bank and the UN focused heavily on avoiding ongoing losses of soil carbon by clearing more forests or plowing up native grasslands. It also called for urgent efforts to rewet drained peatlands used for agriculture and forestry, which occupy only 0.5% of global agricultural land but generate around 2% of all human emissions. But in this chapter, we found that the ability to sequester more carbon on existing agricultural land was highly limited based on the science we know today. 

A blog summarizing this soil carbon story available here, drew some comments.  They included a conment claiming that that we underestimated this potential by Keith Paustian and others, and a comment by David Powlson and others endorsing our conclusion.  They are available on this page.