No-Till Systems to Sequester Soil Carbon: Potential and Reality

The conversion of soils from conventional till (CT) to no-till (NT) management has been identified as a soil management practice with the potential to increase soil organic carbon (SOC) sequestration and help mitigate global climate change. However, the changes in SOC observed in NT systems have often been variable and dependent on a combination of factors, including climate, cropping system, soil type and crop/soil management. This had led to large variation in the rates of sequestration observed worldwide. In addition, there is concern some studies may have overestimated SOC sequestration rates due to methodological issues, with some authors concluding that once these methodological factors are considered, the potential for NT to sequester C on a worldwide scale may be limited. When the effect of NT on N2O and CH4 emissions are also considered, the benefits of NT management to mitigate climate change can be further eroded and NT may even increase net greenhouse gas (GHG) emissions - for example from fine textured and poorly drained soils where NT management increases N2O emissions. However, the potential for net C sequestration in NT systems is site specific and where site conditions/management favor SOC accumulation and lead to neutral or decreases in N2O production, significant decreases in global warming potential (GWP) can be observed. This highlights the need to consider the net GWP of NT on a soil type, site or regional basis.