Soil organic carbon sequestration with depth distribution is sensitive to land management

Authors: Franzluebbers, Alan

Submitted to: Agricultural & Environmental Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2021
Publication Date: 1/20/2022
Citation: Franzluebbers, A.J. 2022. Soil organic carbon sequestration with depth distribution is sensitive to land management. Agricultural and Environmental Letters. 86:79-91. https://doi.org/10.1002/saj2.20346.
DOI: https://doi.org/10.1002/saj2.20346

Interpretive Summary: Measuring and monitoring changes in soil organic C (SOC) concentrations and stocks are important for understanding ecosystem functions. Sequestration of SOC has traditionally been measured from resource-intensive studies over extended periods of time, but an alternative approach of calculating root-zone SOC enrichment is described here as a proxy for estimating SOC sequestration using nonlinear distribution of SOC concentration in the surface 30 cm. From literature data across 52 studies, estimated SOC concentration at 30-cm depth was not different between pairs of conservation management and conventional-till cropland, suggesting support for the concept of using SOC concentration at 30-cm depth as a baseline concentration from which enrichment can be calculated. Root-zone SOC enrichment across this (n = 420) and an earlier study (n = 171) was 12.0 ± 0.6 Mg C ha–1 (mean ± SE) under conventional-till cropland (n = 209), 16.1 ± 0.6 Mg C ha–1 under no-till cropland (n = 269), 20.6 ± 1.0 Mg C ha–1 under grassland (n = 90), and 25.8 ± 3.8 Mg C ha–1 under woodland (n = 23). Regional climatic conditions and soil texture were important in influencing baseline SOC storage and total SOC stock but were minor factors in affecting root-zone SOC enrichment with conservation management. Root-zone SOC enrichment is a relatively simple and straightforward calculation method to indicate SOC sequestration, and if deployed across a diversity of management and farm locations, could lead to better SOC stock inventories and analyses of how contemporary management influences SOC stock change in different ecoregions.

Technical Abstract: Measuring and monitoring of soil organic carbon (SOC) is important for understanding ecosystem functions. Although sequestration of SOC has traditionally involved resource-intensive studies over extended periods of time, an alternative approach was used here based on a non-linear change in SOC concentration in the surface 30 cm of soil. Using literature data across 52 studies, SOC concentration at 30-cm depth was no greater in paired observations between conservation management and conventional-till cropland, suggesting little evidence of deep sequestration of SOC. However, progressively greater SOC sequestration in the upper 30 cm was observed with no-till cropland (6.1 +/- 0.7 Mg C/ha), grassland (6.0 +/- 2.5 Mg C/ha), and woodland (17.3 +/- 3.6 Mg C/ha) than with conventional-till cropland. Utilization of this alternative method of calculation would allow SOC sequestration estimates to be obtained from a greater diversity of management systems and farm conditions.