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Existing estimates of the climate mitigation potential from cropland carbon sequestration (C‐sequestration) are limited because they tend to assume constant rates of soil organic carbon change over all available cropland area, use relatively coarse land delineations, and often fail to adequately consider the agronomic and socioeconomic dimensions of agricultural land use. This results in an inflated estimate of the C‐sequestration potential. We address this gap by defining a more appropriate land base for cover cropping in the United States for C‐sequestration purposes: stable croplands in annual production systems that can integrate cover cropping without irrigation. Our baseline estimate of this suitable stable cropland area is 32% of current U.S. cropland extent. Even an alternative, less restrictive definition of stability results in a large reduction in area (44% of current U.S. croplands). Focusing cover crop implementation to this constrained land base would increase durability of associated C‐sequestration and limit soil carbon loss from land conversion to qualify for carbon‐specific incentives. Applying spatially‐variable C‐sequestration rates from the literature to our baseline area yields a technical potential of 19.4 Tg CO2e yr−1 annually, about one‐fifth of previous estimates. We also find the cost of realizing about half (10 Tg CO2e yr−1) of this potential could exceed 100 USD Mg CO2e−1, an order of magnitude higher than previously thought. While our economic analyses suggest that financial incentives are necessary for large‐scale adoption of cover cropping in the U.S., they also imply any C‐sequestration realized under such incentives is likely to be additional. Plain Language Summary: As a "Nature‐based Climate Solution" (NCS), the practice of cover cropping has received widespread attention and investment recently. Through cover cropping, croplands may be able to absorb and hold more carbon in soil, drawing down CO2 in the atmosphere (i.e., sequester carbon). However, the sequestration that is feasible, which reflects socioeconomic and land use considerations, remains unquantified. We estimate this feasible potential for carbon sequestration in the U.S. croplands from cover cropping and find it to be a fraction of previous estimates. A large portion of the reduction is due to our use of a more realistic and rigorous definition of the land area suitable for cover cropping for climate mitigation purposes. This land area comprises "croplands remaining croplands" (or stable croplands) that are planted to annual crops, like corn and soybeans, because they can more easily integrate the practice. We exclude irrigated croplands to conserve water resources. At just under 44 million ha, our baseline area estimate is 32% of the current U.S. cropland extent. The rest of the reduction is associated with our use of more conservative rates of increase in soil carbon from cover cropping than earlier studies that are more realistic for assessing soil carbon sequestration potential over large areas. Our economic analyses suggests that without financial incentives, implementing cover cropping could be expensive for most U.S. farmers. This high cost hurdle needs to be evaluated against the cost‐effectiveness of alternatives that compete for the same limited resources for climate mitigation. Key Points: For U.S. croplands, the feasible potential of carbon sequestration from cover cropping is a fraction of previous estimatesDefining the land base suitable for mitigation practices more realistically and rigorously is critical to estimating the feasible potentialCover cropping, though beneficial for soil health, may not be a low‐cost pathway for climate mitigation at scale in the U.S. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) sequestration in agricultural soils is an important tool for climate change mitigation within the EU soil strategy for 2030 and can be achieved via the adoption of soil management strategies (SMS). These strategies may induce synergistic effects by simultaneously reducing greenhouse gas (GHG) emissions and/or nitrogen (N) leaching. In contrast, other SMS may stimulate emissions of GHG such as nitrous oxide (N2O) or methane (CH4), offsetting the climate change mitigation gained via SOC sequestration. Despite the importance of understanding trade‐offs and synergies for selecting sustainable SMS for European agriculture, knowledge on these effects remains limited. This review synthesizes existing knowledge, identifies knowledge gaps and provides research recommendations on trade‐offs and synergies between SOC sequestration or SOC accrual, non‐CO2 GHG emissions and N leaching related to selected SMS. We investigated 87 peer‐reviewed articles that address SMS and categorized them under tillage management, cropping systems, water management and fertilization and organic matter (OM) inputs. SMS, such as conservation tillage, adapted crop rotations, adapted water management, OM inputs by cover crops (CC), organic amendments (OA) and biochar, contribute to increase SOC stocks and reduce N leaching. Adoption of leguminous CC or specific cropping systems and adapted water management tend to create trade‐offs by stimulating N2O emissions, while specific cropping systems or application of biochar can mitigate N2O emissions. The effect of crop residues on N2O emissions depends strongly on their C/N ratio. Organic agriculture and agroforestry clearly mitigate CH4 emissions but the impact of other SMS requires additional study. More experimental research is needed to study the impact of both the pedoclimatic conditions and the long‐term dynamics of trade‐offs and synergies. Researchers should simultaneously assess the impact of (multiple) agricultural SMS on SOC stocks, GHG emissions and N leaching. This review provides guidance to policymakers as well as a framework to design field experiments and model simulations, which can address knowledge gaps and non‐intentional effects of applying agricultural SMS meant to increase SOC sequestration. [ABSTRACT FROM AUTHOR]

Land use change (LUC) alters the global carbon (C) stock, but our estimation of the alteration remains uncertain and is a major impediment to predicting the global C cycle. The uncertainty is partly due to the limited number and geographical bias of observations, and limited exploration of its predictors. Here we generated a comprehensive global database of 5,980 observations from 790 articles. The number of sites evaluated is at least seven times larger than in previous meta‐analyses. Our constrained estimates of different LUC's effects on soil organic C (SOC) and their variations across global climates reveal underestimation/overestimation in previous estimates. Converting forests and grasslands to croplands reduced SOC by 24.5% ± 1.53% (−11.03 ± 1.06 Mg ha−1) and 22.7% ± 1.22% (−8.09 ± 0.67 Mg ha−1), while 28.0% ± 1.56% (4.46 ± 0.42 Mg ha−1) and 33.5% ± 1.68% (5.8 ± 0.38 Mg ha−1) increases, respectively, were obtained in the reverse processes. Converting forests to grasslands decreased SOC by 2.1% ± 1.22% (−1.13 ± 0.44 Mg ha−1), while the reverse process increased SOC by 18.6% ± 1.73% (3.31 ± 0.51 Mg ha−1). Modeled relative importance of 10 drivers of LUC's impact on SOC revealed that higher initial SOC (iSOC) does not solely determine SOC loss in SOC‐negative LUC scenarios as previously proposed. Across four decades, reconverting croplands to forests and grasslands recovered only 49.5% (6.1 ± 0.51 Mg ha−1) and 75.3% (7.0 ± 0.38 Mg ha−1) of the iSOC, respectively, indicating the need for protecting C‐rich ecosystems. Our global data set advances information on LUC's effect on SOC and can be valuable to constrain Earth system models to reliably estimate global SOC stocks and plan climate change mitigation strategies. Plain Language Summary: Land use change (LUC) could increase or decrease the global soil organic carbon (SOC) stock and affect carbon cycling and climate change, but estimating its effect size is the most uncertain aspect of the global carbon cycle. Available estimates vary among studies, most of which often use few observations that do not cover most global regions. To provide more accurate estimates of different LUC types' effects on SOC, we compiled a comprehensive database that contains 5,980 observations across all global regions; and revealed that previous studies have underestimated/overestimated these effects. We modeled the predictors of SOC change and found that previous conclusions that higher initial SOC is the main reason for higher organic carbon loss under negative LUC scenarios were inexact. We show that land use practices aimed at restoring SOC could only recover part of the amount lost during similar time frames; hence, it is important to protect carbon‐rich ecosystems. Our study provides robust estimates of LUC's effect on SOC and provides data sets that can reliably assess and model the global carbon cycle and plan strategies for controlling global climate change. Key Points: Comprehensive global database advances robust estimates of land use change's (LUCs) effect on soil organic carbon (SOC) vital for Earth system modelingHigher initial SOC does not solely control rapid SOC loss in carbon‐negative LUC as often proposedDespite SOC buildup in the past four decades, the amount lost cannot be regained by restoration during similar time frames [ABSTRACT FROM AUTHOR]

Nature‐based climate solutions (NCS) are championed as a primary tool to mitigate climate change, especially in forested regions capable of storing and sequestering vast amounts of carbon. New England is one of the most heavily forested regions in the United States (>75% forested by land area), and forest carbon is a significant component of climate mitigation policies. Large infrequent disturbances, such as hurricanes, are a major source of uncertainty and risk for policies relying on forest carbon for climate mitigation, especially as climate change is projected to alter the intensity and extent of hurricanes. To date, most research into disturbance impacts on forest carbon stocks has focused on fire. Here, we show that a single hurricane in the region can down between 121 and 250 MMTCO2e or 4.6%–9.4% of the total aboveground forest carbon, much greater than the carbon sequestered annually by New England's forests (16 MMTCO2e year−1). However, emissions from hurricanes are not instantaneous; it takes approximately 19 years for downed carbon to become a net emission and 100 years for 90% of the downed carbon to be emitted. Reconstructing hurricanes with the HURRECON and EXPOS models across a range of historical and projected wind speeds, we find that an 8% and 16% increase in hurricane wind speeds leads to a 10.7‐ and 24.8‐fold increase in the extent of high‐severity damaged areas (widespread tree mortality). Increased wind speed also leads to unprecedented geographical shifts in damage, both inland and northward, into heavily forested regions traditionally less affected by hurricanes. Given that a single hurricane can emit the equivalent of 10+ years of carbon sequestered by forests in New England, the status of these forests as a durable carbon sink is uncertain. Understanding the risks to forest carbon stocks from disturbances is necessary for decision‐makers relying on forests as a NCS. [ABSTRACT FROM AUTHOR]

The effects of releasing carbon from the terrestrial pool into the atmosphere have significant long‐term and short‐term implications that affect many parts of our globe. Agricultural fields might help to address these concerns and provide cost‐effective solutions, such as lowering carbon dioxide levels (CO2) in the atmosphere while raising carbon levels in the soil. In order to increase agricultural land's potential to absorb and store carbon, the proper selection of suitable microbial inoculants with the capability to sequester carbon into soils is critical. Soil quality and characteristics would improve as a result, and atmospheric carbon would therefore be reduced. Soil microbes have the potential to influence the level of organic matter, which has an impact on the soil's ecological system and characteristics. Soil microbes play a role in carbon sequestration in soils by regulating multiple and distinct pathways for CO2 inputs and losses, such as biochemical processes that could sequester CO2, the capacity to sediment carbonates, the rigid nature of their components and vegetative tissues, or the composition of complex substances that preserve carbon in the soil. Further research is needed to investigate if particular microbial strains that can sequester carbon will help enhance soil quality and prevent climate change. [ABSTRACT FROM AUTHOR]

Biosolids can build soil organic matter, but their ability to increase carbon and nitrogen in persistent fractions in deep soil is not well understood. We aimed to assess the mechanisms that influence soil carbon and nitrogen dynamics at three sites—Sacramento (irrigated, grazed grassland), Solano (rainfed, grazed grassland), and Merced (feed cropping system with alfalfa–corn rotation)—where soils were amended with biosolids for 20 years using density fractionations, organomineral extractions, and correlations between calcium and soil organic carbon at three depths (0–10, 30–50, and 75–100 cm). We found that amended soils had higher carbon and nitrogen content in the free‐ and occluded‐light fractions at all depths relative to the control in the Sacramento and Solano sites; however, the Merced site had a greater relative increase of carbon and nitrogen associated with the heavy fraction. Effect sizes show that biosolids increase carbon and nitrogen content in free‐ and occluded‐light fractions in the surface soil (0–10 cm), and in both light and heavy fractions in the deep soil layer (75–100 cm). Ratios of carbon to iron and aluminum show that chelation is an important mechanism of carbon stabilization in Sacramento and Solano sites throughout the soil profile. No (0–10 cm) to negative (75–100 cm) correlations were observed between calcium and soil carbon in the amended soils in the Merced site. Our results indicate that, while biosolids are typically incorporated at shallow depths, long‐term application of biosolids can increase the amount of free‐ and occluded‐light carbon fractions in deep soil. Core Ideas: Long‐term biosolids increased deep soil C and N concentrations.Density fractionation indicates amended soils had more labile C and N in surface soils.Organometal complexes were a stabilization mechanism in two of the three sites.Negative correlations between C and Ca2+ in amended soils indicate biosolids interact with C.Accounting for deep soil C demonstrated the importance of assessing the climate change mitigation potential of managed soil. [ABSTRACT FROM AUTHOR]

Among options for atmospheric CO2 removal, sequestering soil organic carbon (SOC) via improved grazing management is a rare opportunity because it is scalable across millions of globally grazed acres, low cost, and has high technical potential. Decades of scientific research on grazing and SOC has failed to form a cohesive understanding of how grazing management affects SOC stocks and their distribution between particulate (POM) and mineral‐associated organic matter (MAOM)—characterized by different formation and stabilization pathways—across different climatic contexts. As we increasingly look to grazing management for SOC sequestration on grazinglands to bolster our climate change mitigation efforts, we need a clear and collective understanding of grazing management's impact on pathways of SOC change to inform on‐the‐ground management decisions. We set out to review the effects of grazing management on SOC through a unified plant ecophysiology and soil biogeochemistry conceptual framework, where elements such as productivity, input quality, soil mineral capacity, and climate variables such as aridity co‐govern SOC accumulation and distribution into POM and MAOM. To maximize applicability to grazingland managers, we discuss how common management levers that drive overall grazing pattern, including timing, intensity, duration, and frequency can be used to optimize mechanistic pathways of SOC sequestration. We discuss important research needs and measurement challenges, and highlight how our conceptual framework can inform more robust research with greater applicability for maximizing the use of grazing management to sequester SOC. [ABSTRACT FROM AUTHOR]

Formation of forest islands in West Africa has been linked to anthropogenic soil improvement resulting in luxuriant tree growth in otherwise open savanna landscapes. However, there is limited understanding of how such unique ecosystems modulate soil carbon (C) dynamics and nutrient cycling. In this study, we report soil nutrient characteristics and two distinct soil organic carbon pools of Anogeissus grove (forest island) associated with abandoned village sites of the Mole National Park in the Guinea savanna or tropical continental climatic zone of Ghana, taking opportunity of a previously published study in Biotropica in 1978. We compared present‐day differences in soil characteristics between the previously studied forest grove and adjoining open savanna in the Park and evaluated vegetation dynamics since first measurement in 1974. Overall, we see changes related to self‐thinning and expansion of the grove on a decadal timescale. Soil organic matter and available phosphorus contents were greater in the grove and increased by 19.6% and 18.7%, respectively over time, showing persistence after four decades. Mineral‐associated organic carbon (MAOC) differed significantly (p <.05) between the vegetation types, being 3.44% in the grove and 2.34% in the savanna. The grove was ca. 25% greater in particulate organic carbon (POC) content than the savanna. In both vegetation types, >55% of carbon was stabilized in the mineral fraction. Our study demonstrates long‐term human impacts on soil and vegetation and offers a clear nature‐based solution for climate change mitigation through sustainable land management by indigenous people toward achievement of the "4p1000" initiative. [ABSTRACT FROM AUTHOR]

The term carbon (C) sequestration has not just become a buzzword but is something of a siren's call to scientific communicators and media outlets. Carbon sequestration is the removal of C from the atmosphere and the storage, for example, in soil. It has the potential to partially compensate for anthropogenic greenhouse gas emissions and is, therefore, an important piece in the global climate change mitigation puzzle. However, the term C sequestration is often used misleadingly and, while likely unintentional, can lead to the perpetuation of biased conclusions and exaggerated expectations about its contribution to climate change mitigation efforts. Soils have considerable potential to take up C but many are also in a state of continuous loss. In such soils, measures to build up soil C may only lead to a reduction in C losses (C loss mitigation) rather than result in real C sequestration and negative emissions. In an examination of 100 recent peer‐reviewed papers on topics surrounding soil C, only 4% were found to have used the term C sequestration correctly. Furthermore, 13% of the papers equated C sequestration with C stocks. The review, further, revealed that measures leading to C sequestration will not always result in climate change mitigation when non‐CO2 greenhouse gases and leakage are taken into consideration. This paper highlights potential pitfalls when using the term C sequestration incorrectly and calls for accurate usage of this term going forward. Revised and new terms are suggested to distinguish clearly between C sequestration in soils, SOC loss mitigation, negative emissions, climate change mitigation, SOC storage, and SOC accrual to avoid miscommunication among scientists and stakeholder groups in future. [ABSTRACT FROM AUTHOR]

Community gardens, as common spaces where people gather to grow food, help foster public health, greener urban environments, life-long learning and vibrant communities. However, despite being promoted as sustainable horticulture and conservation agriculture, their soil health and carbon (C) sequestration potential, with implication for climate change mitigation, remains underexplored. This study assessed soil samples collected from raised beds (gardening area) and adjacent bare ground (control) at six community gardens in the Perth metropolitan area, Australia. These sites covered three soil mapping units (SMUs): calcareous deep sands, coloured sand and pale sands The soil in raised beds exhibited superior characteristics than surrounding urban soil including lower bulk density, higher pH buffering capacity, available nutrients including nitrogen (N), phosphorus (P) and potassium (K), cation exchange capacity (CEC), total C and microbial biomass. Notably, we estimated that raised bed soils accumulated significant levels of C in the top 10 cm layer (0.55 kg/m2 or 5.5 T/ha). Our findings also indicate no significant heavy metal contamination in any of the community garden soils. Although the global area of community gardens is marginally small, these results suggest they hold potential for carbon sequestration, especially in urban and peri-urban environments. The improved soil health and C storage potential in community garden soil are largely attributed to the regular application of compost produced within the community gardens. [ABSTRACT FROM AUTHOR]

Delineation of carbon management zones (CMZs) by capturing geospatial distribution of soil organic carbon (SOC) stock down the profile is an effective strategy for precision agriculture and climate change mitigation. Satellite (Landsat OLI 8), terrain (SRTM 30 m DEM) and bioclimatic (WorldClim dataset) factors were used as covariables in this digital soil mapping approach. Depth harmonization using the quadratic spline method (equal-area) was carried out prior to quantile regression forest (QRF) algorithm-based modelling to estimate SOC stock at six standard soil depths (0-5, 5-15, 15-30, 30-60, 60-100 and 100-200 cm). Soil depth and SOC stock for the whole soil profile were used for the delineation of CMZs using fuzzy k-means clustering. The predicted SOC stock, varied from 14.68 to 42.35 Mg ha-1 in the top layer (0-5 cm depth), while 17.91 to 36.88, 14.15 to 34.70, 12.55 to 35.59, 10.30 to 28.52 and 7.26 to 20.16 Mg ha-1 in the depths of 5-15, 15-30, 30-60, 60-100 and 100-200 cm, respectively. The QRF algorithm performed well in predicting SOC stock with high R2, which ranged from .67 to .83 for all the soil depths. To delineate three CMZs, modified partitioning entropy and the fuzzy performance index were used. In CMZ2, there was a significant increase in SOC stock, followed by CMZ1 and CMZ3. This zone (CMZ2) was located in the central region of the study area and was mostly covered by dense forest and perennial plantations (rubber). The CMZs provided the necessary foundation for the development of site-specific carbon management techniques that can enhance ecosystem service and meet climate change mitigation goals. [ABSTRACT FROM AUTHOR]

There is growing awareness of the potential value of agricultural land for climate change mitigation. In Sweden, cropland areas have decreased by approximately 30% over recent decades, creating opportunities for these former croplands to be managed for climate change mitigation by increasing soil organic carbon (SOC) stocks. One potential land-use change is conversion of cropland to grazed grasslands, but the long-term effect of such change in management is not well understood and likely varies with soil type and site-specific conditions. Through sampling of mineral and peatland soils within a 75-year chronosequence of land converted from crop production to grazed grassland, we assessed how time since conversion, catenary position, and soil depth affected SOC storage. The SOC stocks calculated at an equivalent soil or ash mass increased through time since conversion in mineral soils at all topographic positions, at a rate of ~0.65% year-1. Soils at low topographic positions gained the most carbon. Peat SOC stock gains after conversion were large, but only marginally significant and only when calculated at an equivalent ash mass. We conclude that the conversion of mineral soil to grazed grassland promotes SOC accumulation at our sites, but climate change mitigation potential would need to be evaluated through a full greenhouse gas balance. [ABSTRACT FROM AUTHOR]

The article discusses the importance of time in accurately defining and quantifying carbon sequestration in soils for climate change mitigation. The authors argue that the definition proposed by Don et al. is incomplete because it does not explicitly consider the time that carbon remains stored in an ecosystem. They emphasize that a comprehensive definition should include both the amount of carbon sequestered and the duration of its storage. The authors suggest that considering time in the definition of carbon sequestration is crucial for effective climate change actions. [Extracted from the article]

The article discusses the importance of soil carbon sequestration (SCS) as a tool to mitigate climate change. The authors estimate that agricultural soils have the potential to sequester 3-14 Gt CO2/year by 2050 through SCS practices. They emphasize that SCS should be implemented alongside emission reductions in all sectors. The article also highlights the need for better estimates of biomass availability for SCS practices and acknowledges the variability in carbon loss and saturation levels. The authors argue that undervaluing the potential of SCS can lead to inaction on climate change. [Extracted from the article]

The article "Climate change mitigation through soil carbon sequestration in working lands: A reality check" questions the validity and realism of claims made by Almaraz et al. regarding the potential magnitude of soil carbon sequestration (SCS) in agricultural soils. The authors argue that Almaraz et al. overestimate the availability of organic matter for compost and biochar, inaccurately interpret carbon sequestration rates, and make premature assumptions about the applicability of enhanced rock weathering. They emphasize the need for realistic evaluations of the limitations and trade-offs of SCS practices and caution against overly optimistic estimates that can mislead policymakers. The authors declare no conflicts of interest. [Extracted from the article]

Munoz et al. (2024) raised concerns regarding our recent contribution and the definition of the term C sequestration in soils (Don et al., 2024). We performed a review and therefore based our analysis on existing definitions of C sequestrations, mainly by the IPCC. We recommend sticking with terminologies around C sequestration and climate mitigation, as outlined in our review, in order to keep it consistent and manageable. [ABSTRACT FROM AUTHOR]