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Soils are integral to the function of all terrestrial ecosystems and to food and fibre production. An overlooked aspect of soils is their potential to mitigate greenhouse gas emissions. Although proven practices exist, the implementation of soil-based greenhouse gas mitigation activities are at an early stage and accurately quantifying emissions and reductions remains a substantial challenge. Emerging research and information technology developments provide the potential for a broader inclusion of soils in greenhouse gas policies. Here we highlight 'state of the art' soil greenhouse gas research, summarize mitigation practices and potentials, identify gaps in data and understanding and suggest ways to close such gaps through new research, technology and collaboration.
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There are currently 180 million hectares under pasture in Brazil, and despite the country being one of the largest meat producers, there remain around 64 million hectares that show signs of degradation and contribute to the substantial loss of soil organic carbon (SOC). The aim of this study, therefore, was to derive the factors for SOC stock changes in managed pastures and evaluate the potential for SOC sequestration when converting degraded pastures to well-managed or recovered pastures in Brazil. The study involved 169 paired comparisons, including different types of pasture spread over 14 states in Brazil, and analysed the data in linear mixed-effect models deriving the SOC stock change factors for various soil depths (30 to 100 cm) over 30 years since the change in management. The results showed that for 30 years at a depth of 0–30 cm, compared to native vegetation, nominal pasture (non-degraded grassland, but with no significant management improvements) and improved pasture increased SOC stocks by 15% and 8%, whilst degraded pastures reduced the stocks by 10%. However, the recovery of degraded pastures enhances the SOC by 23%. In terms of the rates of SOC change, pasture degradation leads to losses of 0.25 Mg C ha⁻¹ year⁻¹, whilst nominal or recovered pastures can sequester SOC at rates from 0.25 to 0.54 Mg ha⁻¹ year⁻¹. Overall, it was estimated that the recovery of degraded pastures can sequester up to 3445 Tg of CO2. Nominal management or simple improvement practices can maintain or enhance SOC stocks, helping to mitigate the GHG emissions of livestock in Brazil.
Article
Biochar, included as a soil amendment by EU Regulation 2019/1009, has been shown to increase soil organic C stock and nutrient retention. We investigated the effect of biochar incorporation alone (B) and in association with mineral (BMin), digestate (BDig) and slurry (BSlu) fertilization, compared to the respective controls without biochar (C, Min, Dig and Slu), in a silage maize–Italian ryegrass rotation, on yield, soil fertility parameters and nitrous oxide (N2O) emissions. Two types of biochar in three doses (0.2, 0.45, 0.9%) were tested in two cropping seasons. Biochar did not significantly affect maize yield; however, BDig tended to increase silage yield and the ear component compared to Dig, while BMin tended to reduce maize N uptake compared to Min. Biochar incorporation significantly increased soil organic C (+31%) and cation exchange capacity (CEC) (+13%) in all the fertilization treatments; BMin and BDig also showed an increase compared to biochar alone (B). Emission of N2O was mainly driven by fertilization, digestate exhibiting the highest emissions. Biochar addition decreased the cumulative N2O emissions consistently in all the fertilization treatments, though not significantly. The association of biochar with organic fertilizers, in particular digestate, appears promising in increasing the fertilizer efficiency and reducing N2O emissions.
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From hillslope to small catchment scales (< 50 km2), soil carbon management and mitigation policies rely on estimates and projections of soil organic carbon (SOC) stocks. Here we apply a process-based modeling approach that parameterizes the MIcrobial-MIneral Carbon Stabilization (MIMICS) model with SOC measurements and remotely sensed environmental data from the Reynolds Creek Experimental Watershed in SW Idaho, USA. Calibrating model parameters reduced error between simulated and observed SOC stocks by 25%, relative to the initial parameter estimates and better captured local gradients in climate and productivity. The calibrated parameter ensemble was used to produce spatially continuous, high-resolution (10 m2) estimates of stocks and associated uncertainties of litter, microbial biomass, particulate, and protected SOC pools across the complex landscape. Subsequent projections of SOC response to idealized environmental disturbances illustrate the spatial complexity of potential SOC vulnerabilities across the watershed. Parametric uncertainty generated physicochemically protected soil C stocks that varied by a mean factor of 4.4 × across individual locations in the watershed and a − 14.9 to + 20.4% range in potential SOC stock response to idealized disturbances, illustrating the need for additional measurements of soil carbon fractions and their turnover time to improve confidence in the MIMICS simulations of SOC dynamics.
Article
Human-induced climate change is one of the most pressing challenges of our time. The Helmholtz Association is making essential research contributions to mitigate the causes and impacts of climate change and find ways to adapt. The “Net-Zero-2050” project, the Cluster I of the Helmholtz Climate Initiative, scientifically investigates and evaluates strategies and new ways to reduce, extract and permanently store carbon emissions. Two digital knowledge transfer products (DKTPs) were developed to present the complex research results comprehensively: (1) the “Net-Zero-2050 Web-Atlas” provides information on methods and technologies for CO2 reduction and possible reduction paths; (2) the “Soil Carbon App” provides simulated soil carbon data to estimate climate protection potentials through different land management methods. Both formats intend to support users in making informed decisions and developing appropriate climate neutrality strategies. During the two DKTPs development, common main challenges were identified regarding concepts and stakeholder involvement. Along with that, specific approaches to solving the tasks could be distilled for each product. In the still-evolving arena of digital knowledge transfer, no standard methods can be applied. At the same time, communication of climate research results to decision-makers is becoming more and more relevant. This paper extracts the challenges and gives approaches to facilitate a transfer of the gained experience to future similar projects.
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Soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions are two main greenhouse gases that play important roles in global warming. Studies have shown that microplastics, biochar, and earthworms can significantly affect soil greenhouse gas emissions. However, few studies have explored how their interactions affect soil CO2 and N2O emissions. A mesocosm experiment was conducted to investigate their interactive effects on soil greenhouse gases and soil microbial functional genes in vegetable-growing soil under different incubation times. Biochar alone or combined with microplastics significantly decreased soil CO2 emissions but had no effect on soil N2O emissions. Microplastics and biochar inhibited CO2 emissions and promoted N2O emissions in the soil with earthworms. The addition of microplastics, biochar, and earthworms had significant effects on soil chemical properties, including dissolved organic carbon, ammonia nitrogen, nitrate nitrogen, total nitrogen, and pH. Microplastics and earthworms selectively influenced microbial abundances and led to a fungi-prevalent soil microbial community, while biochar led to a bacteria-prevalent microbial community. The interactions of microplastics, biochar, and earthworms could alleviate the reduction of the bacteria-to-fungi ratio and the abundance of microbial functional genes caused by microplastics and earthworms alone. Microplastics significantly inhibited microorganisms as well as C and N cycling functional genes in earthworm guts, while biochar obviously stimulated them. The influence of the addition of exogenous material on soil greenhouse gas emissions, soil chemical properties, and functional microbes differed markedly with soil incubation time. Our results indicated that biochar is a promising amendment for soil with microplastics or earthworms to simultaneously mitigate CO2 emissions and regulate soil microbial community composition and function. These findings contribute to a better understanding of the interaction effects of microplastics, biochar, and earthworms on soil carbon and nitrogen cycles, which could be used to help conduct sustainable environmental management of soil.
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Purpose Traditional measurement for soil properties is time-consuming and costly, while visible–near-infrared spectroscopy enables the rapid prediction of soil properties. In this study, visible–near-infrared spectroscopy was used to predict these four soil properties including OC (organic carbon) content, TN (total nitrogen) content, pH value, and clay content in rare earth mining areas based on different spectral transformation and calibration methods. Materials and methods A total of 232 soil samples were collected from unexploited, in situ leaching, and heap leaching mining areas in southern Jiangxi Province, China. The chemical properties and reflectance spectra of air-dried samples were measured. Spectral transformations including first-order derivative (FOD), continuum removal (CR), and continuous wavelet transform (CWT) were selected to improve the prediction accuracy of the model. Partial least-squares regression (PLSR), the support vector machine (SVM), and extreme gradient boosting (XGBoost) were used to construct prediction models. Results and discussion The highest prediction accuracies in terms of the coefficient of determination (R²), root mean square error (RMSE), and relative prediction deviation (RPD) were obtained using CWT spectra with XGBoost for organic carbon content (R² = 0.89, RMSE = 0.24, RPIQ = 4.67), total nitrogen content (R² = 0.86, RMSE = 0.01, RPIQ = 4.14), and pH value (R² = 0.73, RMSE = 0.19, RPIQ = 1.66). The best prediction result for clay content was obtained using CWT spectra with the SVM (R² = 0.67, RMSE = 6.45, RPIQ = 2.75). Conclusions The CWT coupled with a non-linear model, such as XGBoost, is an effective method for the accurate prediction of soil properties in rare earth mining areas.
Article
Northern peatlands are an important global climate regulator storing approximately one-third of the global carbon pool, however the degradation of these ecosystems from land-use change can switch peatlands to persistent and long-term sources of atmospheric carbon dioxide. Active restoration is often required to return degraded peatlands to a net carbon sink. The peat-block restoration technique, where intact peat blocks are extracted from a donor peatland and transferred to restore peatlands where the remnant peat is non-existent, contaminated, and/or undergoes seasonal flooding is increasingly being adopted as a peatland restoration technique given the carbon sequestration that can occur immediately post-restoration. However, donor peat blocks often need to be temporarily stockpiled during the restoration process due to logistical constraints. The dewatering of the peat blocks during this stockpiling period may alter hydrophysical peat properties that sustain critical peatland ecohydrological functionality and ultimately affect peatland restoration success. Yet, the hydrophysical evolution of stockpiled peat blocks remains unknown. Here, we examine how peat block stockpiling time (3, 7, 11, and 14 months and a reference site) impacts peat hydrophysical properties and sphagnum moss photosynthesis, both of which are critical for peatland restoration success. Stockpiling peat differentially impacted the hydrophysical properties between the shallower and deeper peats, where little to no impact from stockpiling was observed in the shallower peats, regardless of stockpiling time. Rather, as stockpiling time increased, there was a marked decrease in macroporosity (pores >75 μm) and mobile porosity (drainable porosity at approximately −100 hpa) at depths below 20 cm but the water conducting matrix porosity (defined as mobile porosity minus macroporosity) was not significantly different than the reference samples. However, stockpiling created inhospitable conditions for sphagnum mosses., as chlorophyll fluorescence ratio was below 0.3, indicating little to no photosynthesis of the stockpiled peat during summertime drought conditions. Taken together, we suggest limiting stockpiling time as much as possible would be advantageous for using the stockpiled peat blocks for the peat-block restoration technique or other restoration efforts, such as floating mat creation.
Article
The abundance and structural composition of nitrogen (N) transformation-related microbial communities under certain environmental conditions provide sufficient information about N cycle under different soil conditions. This study aims to explore the major challenge of low N use efficiency (NUE) and N dynamics in aerobic rice systems and reveal the agronomic-adjustive measures to increase NUE through insights into the ecophysiology of ammonia oxidizers. Water-saving practices, like alternate wetting and drying (AWD), dry direct seeded rice (DDSR), wet direct seeding, and saturated soil culture (SSC), have been evaluated in lowland rice; however, only few studies have been conducted on N dynamics in aerobic rice systems. Biological ammonia oxidation is majorly conducted by two types of microorganisms, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). This review focuses on how diversified are ammonia oxidizers (AOA and AOB), whose factors affect their activities and abundance under different soil conditions. It summarizes findings on pathways of N cycle, rationalize recent research on ammonia oxidizers in N-cycle, and thereby suggests adjustive agronomic measures to reduce N losses. This review also suggests that variations in soil properties significantly impact the structural composition and abundance of ammonia oxidizers. Nitrification inhibitors (NIs) especially nitrapyrin, reduce the nitrification rate and inhibit the abundance of bacterial amoA without impacting archaeal amoA. In contrast, some NIs confine the hydrolysis of synthetic N and, therefore, keep low NH 4 +-N concentrations that exhibit no or very slight impact on ammonia oxidizers. Variations in soil properties are more influential in the community structure and abundance of ammonia oxidizers than application of synthetic N fertilizers and NIs. Biological nitrification inhibitors (BNIs) are natural bioactive compounds released from roots of certain plant species, such as sorghum, and could be commercialized to suppress the capacity of nitrifying soil microbes. Mixed application of synthetic and organic N fertilizers enhances NUE and plant N-uptake by reducing ammonia N losses. High salt concentration promotes community abundance while limiting the diversity of AOB and vice versa for AOA, whereas AOA have lower rate for potential nitrification than AOB, and Frontiers in Plant Science | www.frontiersin.org 1 June 2022 | Volume 13 | Article 913204 Farooq et al. Enhancing Nitrogen Use Efficiency denitrification accounts for higher N 2 production. Archaeal abundance, diversity, and structural composition change along an elevation gradient and mainly depend on various soil factors, such as soil saturation, availability of NH 4 + , and organic matter contents. Microbial abundance and structural analyses revealed that the structural composition of AOA was not highly responsive to changes in soil conditions or N amendment. Further studies are suggested to cultivate AOA and AOB in controlled-environment experiments to understand the mechanisms of AOA and AOB under different conditions. Together, this evaluation will better facilitate the projections and interpretations of ammonia oxidizer community structural composition with provision of a strong basis to establish robust testable hypotheses on the competitiveness between AOB and AOA. Moreover, after this evaluation, managing soils agronomically for potential utilization of metabolic functions of ammonia oxidizers would be easier.
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Reversibility of soil carbon sinks is a major obstacle in assigning soil carbon sequestration as negative emission technology and it is still unclear how a non-permanent CO2 removal shall be accounted for. In this study, we combine various scenarios of reversible and non-reversible soil carbon sinks with atmospheric CO2 impulse response functions and calculations of the resulting radiative forcing. A time horizon of up to 500 years was considered. Results show that any soil carbon sink generates negative radiative forcing (i.e., cooling) when aggregated over longer time scales. Whereas also non-permanent CO2 removals from the atmosphere provide negative average radiative forcing, their effect is substantially smaller than that of permanent removals of the same magnitude. We show that the average annual soil organic carbon balance over the integrated time window largely determines the average radiative forcing independently of rates of carbon gain or loss and longevity of the sink. This basic principle allows an unbiased assessment, comparison, and rating of mitigation projects that take advantage of soil carbon. The suggested approach is based on quantitative and relatively simple metrics and may therefore support guidance to climate policies and soil carbon markets.
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As regional and continental carbon balances of terrestrial ecosystems become available, it becomes clear that the soils are the largest source of uncertainty. Repeated inventories of soil organic carbon (SOC) organized in soil monitoring networks (SMN) are being implemented in a number of countries. This paper reviews the concepts and design of SMNs in ten countries, and discusses the contri
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Atmospheric methane is the second most important greenhouse gas after carbon dioxide, and is responsible for about 20% of the global warming effect since pre-industrial times. Rice paddies are the largest anthropogenic methane source and produce 7-17% of atmospheric methane. Warm waterlogged soil and exuded nutrients from rice roots provide ideal conditions for methanogenesis in paddies with annual methane emissions of 25-100-million tonnes. This scenario will be exacerbated by an expansion in rice cultivation needed to meet the escalating demand for food in the coming decades. There is an urgent need to establish sustainable technologies for increasing rice production while reducing methane fluxes from rice paddies. However, ongoing efforts for methane mitigation in rice paddies are mainly based on farming practices and measures that are difficult to implement. Despite proposed strategies to increase rice productivity and reduce methane emissions, no high-starch low-methane-emission rice has been developed. Here we show that the addition of a single transcription factor gene, barley SUSIBA2 (refs 7, 8), conferred a shift of carbon flux to SUSIBA2 rice, favouring the allocation of photosynthates to aboveground biomass over allocation to roots. The altered allocation resulted in an increased biomass and starch content in the seeds and stems, and suppressed methanogenesis, possibly through a reduction in root exudates. Three-year field trials in China demonstrated that the cultivation of SUSIBA2 rice was associated with a significant reduction in methane emissions and a decrease in rhizospheric methanogen levels. SUSIBA2 rice offers a sustainable means of providing increased starch content for food production while reducing greenhouse gas emissions from rice cultivation. Approaches to increase rice productivity and reduce methane emissions as seen in SUSIBA2 rice may be particularly beneficial in a future climate with rising temperatures resulting in increased methane emissions from paddies.
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Carbon is a critical component of soil vitality and is crucial to our ability to produce food. Carbon se-questered in soils also provides a further regulating ecosystem service, valued as the avoided damage from global climate change. We consider the demand and supply attributes that underpin and constrain the emergence of a market value for this vital global ecosystem service: markets being what economists regard as the most efficient institutions for allocating scarce resources to the supply and consumption of valuable goods. This paper considers how a potentially large global supply of soil carbon sequestration is reduced by economic and behavioural constraints that impinge on the emergence of markets, and alternative public policies that can efficiently transact demand for the service from private and public sector agents. In essence, this is a case of significant market failure. In the design of alternative policy options, we consider whether soil carbon mitigation is actually cost-effective relative to other measures in agriculture and elsewhere in the economy, and the nature of behavioural incentives that hinder policy options. We suggest that reducing the cost and uncertainties of mitigation through soil-based measures is crucial for improving uptake. Monitoring and auditing processes will also be required to eventually facilitate wide-scale adoption of these measures.
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Compost amendments to grasslands have been proposed as a strategy to mitigate climate change through carbon (C) sequestration, yet little research exists exploring the net mitigation potential or the long-term impacts of this strategy. We used field data and the DAYCENT biogeochemical model to investigate the climate change mitigation potential of compost amendments to grasslands in California, USA. The model was used to test ecosystem C and greenhouse gas responses to a range of compost qualities (carbon to nitrogen [C:N] ratios of 11.1, 20, or 30) and application rates (single addition of 14 Mg C/ha or 10 annual additions of 1.4 Mg CÁha À1 Áyr À1). The model was parameterized using site-specific weather, vegetation, and edaphic characteristics and was validated by comparing simulated soil C, nitrous oxide (N 2 O), methane (CH 4), and carbon dioxide (CO 2) fluxes, and net primary production (NPP) with three years of field data. All compost amendment scenarios led to net greenhouse gas sinks that persisted for several decades. Rates of climate change mitigation potential ranged from 130 6 3 g to 158 6 8 g CO 2-eqÁm À2 Áyr À1 (where ''eq'' stands for ''equivalents'') when assessed over a 10-year time period and 63 6 2 g to 84 6 10 g CO 2-eqÁm À2 Áyr À1 over a 30-year time period. Both C storage and greenhouse gas emissions increased rapidly following amendments. Compost amendments with lower C:N led to higher C sequestration rates over time. However, these soils also experienced greater N 2 O fluxes. Multiple smaller compost additions resulted in similar cumulative C sequestration rates, albeit with a time lag, and lower cumulative N 2 O emissions. These results identify a trade-off between maximizing C sequestration and minimizing N 2 O emissions following amendments, and suggest that compost additions to grassland soils can have a long-term impact on C and greenhouse gas dynamics that contributes to climate change mitigation.
Book
The ability to accurately monitor, record, report and verify greenhouse gas emissions is the cornerstone of any effective policy to mitigate climate change. Accounting for Carbon provides the first authoritative overview of the monitoring, reporting and verification (MRV) of emissions from the industrial site, project and company level to the regional and national level. It describes the MRV procedures in place in more than fifteen of the most important policy frameworks - such as emissions trading systems in Europe, Australia, California and China, and the United Nations Framework Convention on Climate Change - and compares them along key criteria such as scope, cost, uncertainty and flexibility. This book draws on the work of engineers and economists to provide a practical guide to help government and non-governmental policy makers and key stakeholders in industry to better understand different MRV requirements, the key trade-offs faced by regulators and the choices made by up-and-running carbon pricing initiatives. Analyses how common issues are treated in existing carbon pricing mechanisms - helps readers to understand the key trade-offs faced by regulators when MRV procedures are implemented, and why different regulators may strike a different balance, depending on their specific context Includes 'MRV ID tables' for the policy frameworks and up-and-running carbon pricing schemes that are discussed - allows for easy comparison of the different MRV requirements in different systems Provides cost estimates of MRV and lists the nature and stringency of MRV requirements for most schemes/case studies - allows readers to benchmark MRV systems (particularly those currently being designed) against existing ones