From Baselines to Benchmarks: Using the GSOC-MRV Protocol to quantify SOC Gaps and target Interventions in the FAO RECSOIL Initiative

Quantifying soil organic carbon (SOC) gaps is a practical approach to estimate SOC sequestration potential and to prioritize soil management and climate-mitigation actions. Within the FAO Global Soil Partnership’s RECSOIL initiative we quantified SOC gaps and assessed their climatic and edaphic controls across contrasting environments. Soil sampling design and field procedures followed the FAO GSOC-MRV Protocol, enabling standardized and auditable SOC and soil-health monitoring at farm/project scales.

We analyzed 259 sites across Armenia, Costa Rica, Togo, Ghana, and Mexico, compiling SOC concentration (0–30 cm), texture, mean annual precipitation (MAP), mean annual temperature (MAT), land use (cropland/grassland), and USDA soil order. Data were stratified by country and soil type. SOC gaps were defined as the difference between the stratum-specific 80th percentile SOC benchmark and the observed SOC value, set to zero when observations exceeded the benchmark. Relationships between SOC gaps and explanatory variables were evaluated using generalized least squares (GLS), including a soil-type-specific variance structure to address heteroscedasticity.

Mean SOC gaps (±SD) were 20.8±21.5 g kg⁻¹ in Costa Rica, 8.4±7.2 g kg⁻¹ in Armenia, 3.0±2.9 g kg⁻¹ in Mexico, and 2.9±2.1 g kg⁻¹ in Togo–Ghana. Land use showed no effect, whereas MAP and MAT were significant predictors. Andisols and Mollisols exhibited larger SOC gaps than Alfisols, while Inceptisols showed smaller gaps. Overall, climate and soil properties dominated SOC gap patterns, supporting stratified benchmarks to better target interventions and optimize MRV designs in smallholder-inclusive SOC initiatives.