Is there evidence for significant tillage-induced soil organic C sequestration below the plow layer?

Authors: Franzluebbers, Alan

Submitted to: Advances in Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: 5/19/2021
Publication Date: 12/30/2021
Citation: Franzluebbers, A.J. 2021. Is there evidence for significant tillage-induced soil organic C sequestration below the plow layer? Advances in Soil Science. 1:1-23. https://www.taylorfrancis.com/.

Interpretive Summary: Can significant amounts of soil organic carbon be stored below the surface foot of soil under conservation agricultural aproaches? This was the question posed in a review of literature trying to answer if possible, and to what extent possible, if available evidence were presented. Published literature from three dozen studies was collected and soil organic carbon data analyzed from a total of 71 direct comparisons (more than one comparison in each study due to different cropping systems and/or management approaches tested). The evidence was clear that no tillage compared with conventional plow and/or disk tillage led to significantly greater storages of soil organic carbon in the surface 4 to 8 inches of soil. However, many studies showed that no tillage had less soil organic carbon in lower depths to about 2 feet. On balance over the whole profile to 2 foot depth, soil organic carbon was sometimes greater under no tillage than conventional tillage and more often not different between no tillage and conventional tillage. Available evidence suggests that soil organic carbon is not sequestered below the plow layer to any greater extent under no tillage than under conventional tillage, and more typically, is lower under no tillage than under conventional tillage in the 1 to 2 foot depth of the soil profile. This information will help famers, agricultural advisers, and policy makers understand how conservation agriculture changes the physical environment of the soil.

Technical Abstract: Soil organic carbon (SOC) is a key indicator of agricultural productivity, and it controls many other ecosystem services important to ecological stability and environmental sustainability. How tillage management influences SOC has been a topic of interest for decades, particularly as it relates to location of sequestered C within the soil profile. In a review of available literature, surface soil (i.e. 0-30 cm or often considered the plow layer) is often enriched in SOC with no tillage (NT) compared with conventional inversion tillage (CT). More dramatically, the surface 10 cm of soil under NT is almost always greater in SOC content than under CT, depending on duration of comparison and cropping system C inputs. However, SOC often appears to be redistributed with depth in the profile, resulting in significant declines with NT compared with CT below the surface 10 cm, and sometimes below the surface 30 cm. Various reviews and meta-analyses have concluded that surface SOC sequestration with NT can be affected by the extent of C inputs, cropping system complexity, soil texture, and climatic conditions. Evidence for subsoil sequestration of SOC with NT is lacking and the preponderance of evidence would suggest that whole-profile SOC content is either slightly greater with NT than with CT (due to the large surface-soil effect), or more often not significantly different between tillage systems. Additional analyses described in this report suggest that subsoil organic C is not greatly affected by tillage management, at least in the 30-60-cm layer of soil. Surface SOC accumulation with NT compared with CT is significant and important for delivering improved ecosystem services from agriculture, and this result may be more important than whether SOC can be sequestered deeper in the profile.