Since 1995 the IPCC has promoted carbon sequestration in agricultural soils as a one of many climate change mitigation strategies (IPCC, 1995). In principle, certain “improved” practices such as no-till, cover cropping, and increased crop diversity can result in the long-term storage of excess atmospheric carbon in the soil profile. The adoption of such practices constitutes a change in land management (in contrast to land cover and land use change which have higher carbon sequestration potentials). Government agencies and private enterprises have been keen to promote the development of carbon offset markets in which land managers are paid for carbon sequestered in agricultural landscapes.
One major issue with agriculture-based carbon offsets is that methodologies for quantifying carbon sequestration at the field and landscape scales are poorly developed. Another major issue with agriculture-based carbon offsets is that improved practices most likely can only provide a small amount of carbon storage that can be sold as credits to other economic sectors. Schlesinger (2022) (not open access) states:
“for the United States to mitigate 5% of its current carbon dioxide emissions to the atmosphere, about 0.94 tons of carbon would need to be stored in each hectare of cropland annually……For comparison land abandoned from agriculture typically accumulates carbon at rates of 0.1 to 0.3 mtC/ha/year…….any mitigation of climate change will first require that the agriculture sector become “carbon neutral” so that additional soil carbon sequestration might reduce the content of carbon dioxide in the atmosphere.”
Schlesinger goes on to argue that most improved management practices are not likely to lead to large amounts of net carbon sequestration in agricultural soils due to emissions related to agricultural production and photosynthetic constraints.
Even if agricultural soils have a limited capacity to store anthropogenic carbon emissions, farming practices designed around maximizing carbon sequestration remain important. Carbon sequestration can help the agriculture sector reach “net-zero” emissions (when paired with significant GHG emissions reductions). Additionally, carbon sequestering practices like no-till, cover cropping, and increased crop diversity can provide production benefits which improve soil function such as increased water holding capacity and reduced erosion. From an environmental perspective carbon sequestering practices can reduce soil, air, and water pollution when implemented at broader scales.
In summary, practices designed around carbon sequestration can provide significant benefits. However, the small carbon sequestration capacity of agricultural soils raises questions about the viability of ag.-based carbon offset markets.