Soil organic carbon sequestration calculated from depth distribution

Abstract

Sequestration of organic C in agricultural soils is necessary to improve soil health to meet the challenges of climate change, diminishing biodiversity, water quality deterioration, and rising demands for food and fiber production. New assessment approaches are needed to quantify how conservation agriculture might contribute to soil health improvement and soil organic C (SOC) sequestration. In the southeastern US, conservation management has been repeatedly shown to stratify SOC concentration with depth. Starting immediately below a zone of tillage influence (i.e. 30-cm depth), SOC concentration is rarely affected by management due to low C inputs and high decomposition potential, while concentration increases toward the surface in a non-linear manner, presumably with greater inputs of residue and root inputs and changing temperature and moisture conditions. Using these observations as an ecological foundation, SOC sequestration was calculated as the summation of SOC stock greater than the baseline condition at 30-cm depth. Data from literature sources were mathematically fitted with this new approach as a validation. Two on-farm surveys with different agricultural management practices (5-40 yr) in the southeastern US yielded preliminary estimates of SOC sequestration. The interquartile range of calculated SOC sequestration was 4.2 to 9.4 Mg C ha-1 for conventional-tillage cropland (n = 45 fields), 13.6 to 29.7 Mg C ha-1 for no-tillage cropland (n = 97 fields), and 15.9 to 26.1 Mg C ha-1 for perennial pasture (n = 29 fields).

Root‐zone enrichment of carbon, nitrogen, and soil‐test biological activity under cotton systems in North Carolina

“…interquartile range was 5 to 20 yr), and the time period for continuous disk tillage was assumed as 50 yr. It should be noted that root-zone enrichment of SOC, TSN, and STBA in this study is considered analogous to potential sequestration, but should be considered an index since pre-existing conditions that could affect enrichment estimates are not easily verified, as indicated by Franzluebbers (2021b). In addition, it should be noted that this calculation method only allows root-zone enrichment estimates and not loss estimates, which is a limitation of this approach.…”

“…This assumption was based on lack of management effect on SOC concentration below 30-cm depth across multiple studies, as reviewed and reported in Franzluebbers (2021b). The mathematical separation process between baseline content and root-zone enrichment was also first described in detail in Franzluebbers (2021b). The hypothesis was that root-zone enrichment of SOC, TSN, and STBA would be greater under conservation tillage than under disk tillage.…”

“…Surface residue C, N, and mass, bulk density at 0-10-cm depth, and individual depth concentrations of SOC, TSN, and STBA were reported elsewhere (Franzluebbers, 2021a). The focus in the current study was on the integrated assessment of root-zone enrichment of SOC, TSN, and STBA using a nonlinear depth distribution method, as described in Franzluebbers (2021b).…”

“…Rather than over interpret these data and rely on accumulation rates, it has been suggested that a more appropriate approach for assessing root-zone enrichment using this method would be to calculate the ratio between root-zone enrichment and baseline content (Franzluebbers, 2021b), i.e.…”

“…The assumption was that SOC, TSN, and STBA concentrations at ≥30-cm depth would not be greatly affected by management. This assumption was based on lack of management effect on SOC concentration below 30-cm depth across multiple studies, as reviewed and reported in Franzluebbers (2021b). The mathematical separation process between baseline content and root-zone enrichment was also first described in detail in Franzluebbers (2021b).…”