Knowledge gaps, research strategies and robust assessment methods for soil organic carbon storage in coffee production systems

Abstract. Regenerative agriculture is increasingly promoted in the coffee sector as a strategy to enhance soil health and contribute to climate change mitigation through soil organic carbon (SOC) storage. However, robust evidence on the magnitude and drivers of SOC change in coffee production systems remains fragmented and methodologically inconsistent. We systematically reviewed 80 peer-reviewed studies assessing SOC stocks in coffee systems across major producing regions. Our analysis shows that the literature is dominated by synchronic (space-for-time) approaches (~91 %), while true diachronic studies quantifying SOC stock change over time are rare. Only a minority of studies accounted for soil bulk density differences using equivalent soil mass (ESM) approaches, fewer than half sampled below 30 cm soil depth, and more than half did not report previous land use, an essential determinant of SOC trajectories. Across studies, SOC stocks were generally higher in coffee systems than in annual cropping systems and lower than in natural forests, with agroforestry systems sometimes approaching forest SOC levels. However, reported management effects were highly context-dependent and often confounded by differences in soil type, climate, and land-use history. As a result, current evidence does not allow robust quantification of carbon removal potential in coffee systems, nor reliable attribution of SOC differences to specific management practices. Based on this synthesis, we provide methodological guidance for rigorous SOC research in coffee systems, including recommendations on study design, sampling depth, bulk density correction, laboratory procedures, and reporting standards. We argue that future studies must explicitly define research objectives, baseline trajectories, and the spatial scale and context to which their findings apply and distinguish between SOC stock differences and true sequestration rates. Strengthening experimental designs, harmonizing methodologies, and improving data transparency are essential to generate credible, policy-relevant evidence on SOC storage and climate mitigation in coffee landscapes.