Rémi Cardinael

Soil organic carbon (SOC) and soil total nitrogen (STN) are critical indicators of soil health and vital sinks in agroecosystems. However, knowledge gaps remain regarding how long‐term crop‐livestock integration impacts coupled SOC and STN stocks on commercial versus communal smallholder farms in Africa. This study quantified whole profile SOC and STN stocks under two land‐use types (croplands and grazing lands) and two livestock management facilities (congregation points and corrals), across two adjacent, distinct mixed crop‐livestock farming systems, while evaluating how these land uses influence δ ¹³ C and δ ¹⁵ N isotopic signatures. A commercial farm and an adjacent communal smallholder farm with similar soil types were selected. Soil samples were collected from six depth increments (0–5, 5–10, 10–20, 20–40, 40–70, 70–100 cm) to determine profile‐wide SOC and STN stocks alongside their δ ¹³ C and δ ¹⁵ N signatures. Land‐use and management type impacted SOC and STN stocks more significantly in the communal system ( p < 0.001) than on the commercial farm ( p < 0.05). On the commercial farm, whole‐profile SOC (Mg C ha ⁻¹ ± SE) and STN (Mg N ha ⁻¹ ± SE) stocks peaked in grazing lands (129.7 ± 12.8; 10.32 ± 1.14) and reached minimums at livestock congregation points (68.1 ± 2.7; 7.04 ± 1.16). Conversely, in the communal smallholder system, both stocks peaked sharply at livestock congregation points (150.0 ± 4.6; 12.26 ± 0.27) and were lowest in croplands (56.5 ± 1.5; 5.20 ± 0.20). Deep subsoil layers (40–100 cm) stored a greater relative proportion of total stocks on the commercial farm (36%–43% SOC; 39%–45% STN) than on the smallholder farm (28%–39% SOC; 29%–39% STN). Soil δ ¹⁵ N values increased with depth across all land‐use and management types. Lower δ ¹⁵ N values in commercial croplands compared with smallholder croplands likely reflect higher synthetic fertilizer use, while the highest δ ¹⁵ N values occurred in cattle corrals. Contrary to typical microbial fractionation—where preferential loss of ¹² C during respiration enriches δ ¹³ C at depth—no consistent vertical increase in δ ¹³ C was observed; all land‐use types were enriched, averaging −17‰. Our results demonstrate that, within the narrow range of soil textures evaluated, land‐use and management serve as the primary determinants of SOC and STN stocks and their isotopic signatures. While livestock congregation points create intense, localized nutrient hotspots, their small spatial extent limits their landscape‐scale sequestration. Consequently, adopting conservation practices in commercial croplands as a proactive intervention, and optimizing the management of extensive communal grazing lands and croplands are collectively essential for enhancing regional biogeochemical storage and ecosystem resilience.

Most evidence for temperate agroforestry’s climate mitigation potential comes from carbon gains in vegetation, while empirical estimates of soil organic carbon (SOC) responses remain highly variable. This variability may emerge from differences in study design, soil sampling, and reporting. To evaluate how study design influences estimates of temperate agroforestry SOC storage, we conducted an evidence evaluation of agroforestry climate mitigation studies across temperate Europe, Canada, and the United States. We reviewed 80 peer-reviewed studies of SOC storage across five major temperate agroforestry systems: silvoarable systems, silvopasture, riparian buffers, boundary plantings, and forest farming. We characterized the internal and external validity of the evidence base to understand how well it quantifies the climate mitigation potential of SOC storage and how representative these estimates are of temperate agroforestry systems in practice. We found that although agroforestry likely increases SOC, we cannot precisely estimate the magnitude or rate of storage at scales relevant to carbon accounting and crediting. Existing SOC estimates are primarily derived from methodologically limited studies that often lack information needed to assess study quality, including pre-treatment and repeated measurements, justification for control-site selection, and estimates of uncertainty. Accurate estimation of temperate agroforestry SOC storage will require improvements in empirical study design and reporting. Nevertheless, despite lower quality evidence being more variable, with higher mean estimates of SOC storage potential, the average neutral to positive response of SOC across study designs suggests that the climate mitigation potential of temperate agroforestry interventions is not diminished by soil carbon responses.

Vegetating excavated subsoil is a common practice, such as after the construction of infrastructure or mine rehabilitation. Although hailed as promising for additional carbon storage due to low carbon saturation levels, experimental evidence is scarce of how various pools of organic carbon (fresh or native SOM, mineral-associated or not) behave in revegetated subsoil. Here we compared carbon accrual in unfertilised exposed subsoil and topsoil, with and without vegetation, after 6 months of constant 13C labelling in microcosms under controlled environmental conditions. Due to lower fertility, plant growth was hindered in subsoil, meaning less fresh carbon was transferred into the soil and a decrease in native carbon was observed in both mineral-associated and particulate soil organic carbon pools driven by a positive priming effect. Native carbon also declined in the topsoil particulate organic carbon pool, but increased in the mineral-associated pool, indicating a process of carbon stabilization and transfer from particulate to mineral-associated pools. Plant species identity, root traits, and microbial activity better explained changes in fresh than native carbon. We show that vegetating unfertilized exposed subsoil is not a short-term panacea for additional carbon storage due to its lower fertility and weak capacity for carbon stabilization and that mineral-associated carbon stability depends on soil characteristics, plant species, and carbon origin.

Food security and avoiding land use change in Sub‐Saharan Africa (SSA) requires increasing agricultural productivity, necessitating greater fertilizer use. This may increase soil nitrous oxide (O) emissions, a potent greenhouse gas. This study used Machine learning (ML) models to predict O emissions under future climatic and fertilizer scenarios across SSA. Three models were trained (Random Forest (RF), XGBoost (XGB), and feedforward neural networks (FNN)) on existing forest, grassland, and cropland O measurements. The analysis identified the main drivers influencing O emissions: temperature, soil moisture, rainfall, and fertilizer (cropland). SSA O emissions totaled 253–538 Gg N (1 Gg = g), with forests contributing 119–342 Gg N , grasslands 70–132 Gg N , and croplands 63–64 Gg N . Ranges reflect the full uncertainty across all models. Unexpectedly, severe climate change (SSP5‐8.5 scenario) may decrease total O emissions by 4%–37% across SSA, possibly due to drier soils. However, when climate change was combined with tripled fertilizer use (0–63 to 0–189 kg N ), the models predicted a wide range of cropland emission increases of 6%–23% (XGB–RF), with FNN predicting 139% from baseline projections. These findings highlight that while climate change may reduce overall O emissions from forests and grasslands, agricultural intensification will likely become an increasingly significant emission source. To improve prediction accuracy, more comprehensive O monitoring across SSA is needed. This work underscores the need for international investment in monitoring infrastructure and data repositories to guide sustainable agricultural development and SSA climate policy.

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.

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.

Les systèmes agroforestiers stockent du carbone dans la biomasse des arbres. Cependant leur intérêt ne se limite pas à ce carbone stocké sous forme de bois. En effet, les arbres produisent de grandes quantités de litières, et apportent également du carbone dans les horizons profonds du sol par la mortalité et l’exsudation racinaire. Or, les sols agricoles, ayant de très faibles teneurs en matière organique, ont un potentiel de stockage en carbone bien plus important que les sols forestiers. A ce jour, il n’existe pratiquement pas de travaux permettant d’avoir une estimation de l’impact des arbres agroforestiers sur le carbone du sol. La plupart des études sont en effet menées sur le stockage de carbone dans la biomasse aérienne des arbres. Une étude a ainsi estimé qu’en climat tempéré et pour des densités comprises entre 50 et 100 arbres/ha, le stockage de carbone serait compris entre 1.5 et 4 tC/ha/an, ce qui est très important comparé au potentiel de stockage d’autres systèmes de culture. On se propose donc dans ce travail de contribuer significativement à la connaissance sur les possibilités de stockage de C dans les sols en agroforesterie. Tout d’abord, nous quantifierons les stocks de C dans les parcelles agroforestières et les comparerons aux témoins agricoles. Nous étudierons également l’hétérogénéité spatiale de ces stocks, sous la ligne d’arbres ou sous la culture intercalaire, et ce à différentes profondeurs. Dans un deuxième temps, nous étudierons les entrées de carbone au sol, notamment via la mortalité racinaire des arbres. Puis, nous étudierons les processus liés à la stabilisation de ce carbone dans les horizons profonds du sol. Enfin, nous chercherons à savoir si l’apport de carbone frais dans les horizons du sol ne pourrait pas entraîner une minéralisation d’une partie du carbone stable du sol, phénomène connu sous le nom du priming effect, et qui pourrait jouer un rôle non négligeable dans le bilan de carbone de ces systèmes. La modélisation sera utilisée afin d’estimer le stockage de carbone sur le long terme. L’étude sera menée dans un contexte de système de culture méditerranéen, sur un site expérimental d’exception. L’analyse mécaniste fournira le cadre conceptuel pour la compréhension de la dynamique du C dans d’autres systèmes agroforestiers à l’avenir.

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.