Soil Carbon Dynamics Under Regenerative Agricultural Practices in Semi-Arid Regions
DOI:
https://doi.org/10.5281/zenodo.22795949Keywords:
soil organic carbon, regenerative agriculture, no-till, cover cropping, rotational grazing, compost amendment, semi-arid soils, carbon sequestration, c, RothC modellingAbstract
Semi-arid croplands cover roughly a third of the world's agricultural land yet are routinely treated as poor candidates
for soil carbon restoration because low and erratic rainfall limits plant carbon inputs. We tested this assumption
using a nine-year (2013-2022) paired-site monitoring network of 18 commercial farms across two semi-arid
Mediterranean cropping regions, the Ebro Basin of northeastern Spain and the Thessaly plain of central Greece
(mean annual precipitation 380-460 mm), comparing conventional tillage-based cereal and cereal-legume rotations
against four regenerative management regimes: cover cropping, no-till, rotational sheep grazing of post-harvest
stubble and cover crop residue, and periodic solid compost amendment, each replicated across 3-5 paired fields
sharing soil type and management history. Soil organic carbon stocks were measured at 0-15, 15-30 and 30-60 cm
at three-year intervals using bulk-density-corrected equivalent-soil-mass sampling, and long-term trajectories were
projected to 2050 with a locally calibrated RothC model. Averaged across sites, compost-amended fields accrued
0.54 +/- 0.11 Mg C ha-1 yr-1 in the 0-30 cm layer over the monitoring period, followed by fields combining no-till with
cover cropping (0.37 +/- 0.09 Mg C ha-1 yr-1) and rotationally grazed fields (0.22 +/- 0.08 Mg C ha-1 yr-1), while
conventionally managed control fields showed a small, statistically non-significant decline (-0.05 +/- 0.07 Mg C ha-1
yr-1). Gains were concentrated almost entirely in the 0-15 cm layer; below 30 cm, no treatment differed significantly
from the control after nine years. RothC projections suggested that observed accrual rates would need roughly
25-40 years to raise 0-30 cm stocks by the equivalent of two additional years of typical regional crop residue return,
and that a single severe multi-year drought could erase three to five years of accumulated gains. These results
indicate that regenerative practices can measurably increase soil carbon in semi-arid cereal systems, but at rates
an order of magnitude below those reported for temperate humid croplands, with compost amendment offering the
largest and most reliable gains and shallow-depth concentration and drought sensitivity as persistent constraints on
the pace and durability of sequestration.
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