Soil organic carbon dynamic in artificial soils under different treatments

Artificial soils known as technosols are increasingly promoted as a nature-based solution for land restoration and carbon sequestration, yet their long-term capacity to store and stabilise soil organic carbon (SOC) remains poorly constrained. This study evaluates the dynamics, stability and sequestration potential of carbon in experimentally constructed soils under contrasting mineral and organic amendments in Galicia (NW Spain). Six treatments (including artificial soils with and without biochar and dunite, a dunite residue soil and an untreated control) were monitored at two depths (0–15 and 15–30 cm) over an 11-month field campaign and combined with process-based modelling to assess medium-term SOC trajectories.

A comprehensive laboratory dataset including physico-chemical properties (pH, electrical conductivity, bulk density), nutrient status, and functional carbon fractions (CWE, CHE, REM, CFA, CHA, REC) was analysed using multivariate statistics. Principal component analysis revealed that the first two components explained 65–75% of total variance, with PC1 driven by total and organic carbon and PC2 reflecting carbon quality and stabilisation, largely controlled by C/N ratio. Treatments containing biochar (particularly when combined with dunite) exhibited the highest stocks of recalcitrant carbon and the most advanced progression towards stabilised organic matter.

These experimental data were integrated into a multimodel ensemble (RothC, ICBM, Century, Yasso07, AMG and SG) implemented in R using the SoilR framework. After a 1000-year spin-up, 10-year forward simulations were run under two contrasting carbon-input scenarios (2.8 and 5.8 Mg C ha⁻¹ yr⁻¹). The ensemble showed strong sensitivity to amendment type and carbon inputs. Biochar-based technosols consistently produced the highest SOC stocks, with the biochar + dunite treatment gaining up to +5.3 Mg C ha⁻¹ over 10 years under high-input conditions. Conversely, soils without biochar exhibited either near-equilibrium behaviour or limited sequestration capacity.

Overall, the results demonstrate that combining biochar with mineral amendments creates synergistic mechanisms for long-term carbon stabilisation in artificial soils. The multimodel approach provides a robust framework for quantifying uncertainty and supports the deployment of engineered technosols as effective, scalable carbon sinks in land restoration strategies.