Managing soil organic carbon in agriculture: the net effect on greenhouse gas emissions

A change in agricultural practice can increase carbon sequestration in agricultural soils. To know the net effect on greenhouse gas emissions to the atmosphere, however, we consider associated changes in CO2 emissions resulting from the consumption of fossil fuels, emissions of other greenhouse gases and effects on land productivity and crop yield. We also consider how these factors will evolve over time. A change from conventional tillage to no-till agriculture, based on data for average practice in the U.S., will result in net carbon sequestration in the soil that averages 337 kg C ha(-1) yr(-1) for the initial 20 yr with a decline to near zero in the following 20 yr, and continuing savings in CO2 emissions because of reduced use of fossil fuels. The long-term results, considering all factors, can generally be expected to show decreased net greenhouse gas emissions. The quantitative details, however, depend on the site-specific impact of the conversion from conventional to no-till agriculture on agricultural yield and N2O emissions from nitrogen fertilizer.