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Rangelands provide significant environmental benefits through many ecosystem services, which may include soil organic carbon (SOC) sequestration. However, quantifying SOC stocks and monitoring carbon (C) fluxes in rangelands are challenging due to the considerable spatial and temporal variability tied to rangeland C dynamics as well as limited data availability. We developed the Rangeland Carbon Tracking and Management (RCTM) system to track long‐term changes in SOC and ecosystem C fluxes by leveraging remote sensing inputs and environmental variable data sets with algorithms representing terrestrial C‐cycle processes. Bayesian calibration was conducted using quality‐controlled C flux data sets obtained from 61 Ameriflux and NEON flux tower sites from Western and Midwestern US rangelands to parameterize the model according to dominant vegetation classes (perennial and/or annual grass, grass‐shrub mixture, and grass‐tree mixture). The resulting RCTM system produced higher model accuracy for estimating annual cumulative gross primary productivity (GPP) (R2 > 0.6, RMSE <390 g C m−2) relative to net ecosystem exchange of CO2 (NEE) (R2 > 0.4, RMSE <180 g C m−2). Model performance in estimating rangeland C fluxes varied by season and vegetation type. The RCTM captured the spatial variability of SOC stocks with R2 = 0.6 when validated against SOC measurements across 13 NEON sites. Model simulations indicated slightly enhanced SOC stocks for the flux tower sites during the past decade, which is mainly driven by an increase in precipitation. Future efforts to refine the RCTM system will benefit from long‐term network‐based monitoring of vegetation biomass, C fluxes, and SOC stocks. Plain Language Summary Rangelands play a crucial role in providing various ecosystem services, including potential climate change mitigation through increased soil organic carbon (SOC) storage. Accurate estimates of changes in carbon (C) storage are challenging due to the heterogeneous nature of rangelands and the limited availability of field observations. In this work, we leveraged remote sensing observations, tower‐based C flux measurements from over 60 rangeland sites in the Western and Midwestern US, and other environmental data sets to build the process‐based Rangeland Carbon Tracking and Management (RCTM) modeling system. The RCTM system is designed to simulate the past 20 years of rangeland C dynamics and is regionally calibrated. The RCTM system performs well in estimating spatial and temporal rangeland C fluxes as well as spatial SOC storage. Model simulation results revealed increased SOC storage and rangeland productivity driven by annual precipitation patterns. The RCTM system developed by this work can be used to generate accurate spatial and temporal estimates of SOC storage and C fluxes at fine spatial (30 m) and temporal (every 5 days) resolutions, and is well‐suited for informing rangeland C management strategies and improving broad‐scale policy making. Key Points The Rangeland Carbon Tracking and Monitoring System was calibrated to simulate vegetation type‐specific rangeland C dynamics Regional variability in carbon fluxes and soil organic carbon is well represented by a remote sensing‐driven process modeling approach Soil organic carbon stocks in Western and Midwestern US rangelands increased over the past 20 years due to increased precipitation

A field experiment was performed in Southwest Germany to examine the effects of long-term reduced tillage (2000–2012). Tillage treatments were deep moldboard plow: DP, 25 cm; double-layer plow; DLP, 15 + 10 cm, shallow moldboard plow: SP, 15 cm and chisel plow: CP, 15 cm, each of them with or without preceding stubble tillage. The mean yields of a typical eight-year crop rotation were 22% lower with CP compared to DP, and 3% lower with SP and DLP. Stubble tillage increased yields by 11% across all treatments. Soil nutrients were high with all tillage strategies and amounted for 34–57 mg kg−1 P and 48–113 mg kg−1 K (0–60 cm soil depth). Humus budgets showed a high carbon input via crops but this was not reflected in the actual Corg content of the soil. Corg decreased as soil depth increased from 13.7 g kg−1 (0–20 cm) to 4.3 g kg−1 (40–60 cm) across all treatments. After 12 years of experiment, SP and CP resulted in significantly higher Corg content in 0–20 cm soil depth, compared to DP and DLP. Stubble tillage had no significant effect on Corg. Stubble tillage combined with reduced primary tillage can sustain yield levels without compromising beneficial effects from reduced tillage on Corg and available nutrient content.

[Objectives] To explore the effects of single application of chemical fertilizers on soil carbon fixation capacity and soil fertility under plastic film mulching conditions in eastern Qinghai, and to provide a theoretical basis for realizing the sustainable development of film mulching planting methods in this area. [Methods] The effects of single application of chemical fertilizer cultivation mode under film mulching conditions on the soil organic carbon (SOC), labile organic carbon (LOC), carbon management index (CMI), extractable humus carbon (CHE), humic acid carbon (CHA), and fulvic acid carbon (CFA) in the cultivated layer (0-20 cm) were studied through three consecutive years of field experiments on dryland maize farmland in the eastern Qinghai. [Results] Under the film mulching condition, the SOC, LOC and CMI of the single application of chemical fertilizer cultivation mode were lower than the open field control. CHE, CHA and CFA increased with the increase of planting years, but the degree of increase was generally less than that of the open field control. With the increase of planting years, by 2020, the soil LOC/SOC value of film mulching decreased by 4.97% compared with before the start of the experiment, while the open field control increased by 1.11%; the organic carbon oxidation stability coefficient (KOS) of the film mulching was higher than that of the open field control; the soil CHA/CFA value and PQ value were higher than that of the open field control. [Conclusions] Under the condition of single application of chemical fertilizers, the continuous film mulching cultivation mode reduces the soil carbon fixation capacity, and soil organic carbon tends to be stable, which is not conducive to biological utilization and could reduce the soil fertility and degrade the soil quality, causing adverse effects on the stability of crop yield and sustainable production in the long run.

Aims Long-term application of organic materials has been shown to significantly enhance the content of soil organic matter (SOM), underscoring the critical need to examine the components of soil organic carbon for a deeper understanding of SOM functionalities. Thus, the structural changes and microbial driving mechanisms of water extractable organic matter (WEOM), fulvic acid (FA) and humic acid (HA) were investigated in black soil by a long-term fertilization experiment. Methods This 33-year experiment comprises five treatments: no fertilizer (CK), chemical fertilizer (NPK), chemical fertilizer with low-rate straw (NPKJ1), chemical fertilizer with high-rate straw (NPKJ2), and chemical fertilizer with organic manure (NPKM). We also conducted a detailed study of WEOM, FA, HA, and the microbial community structure in both the 0–20 cm and 20–40 cm soil layers. Results Our findings indicate that organic material application primarily sourced WEOM, FA, and HA from microbial metabolism and plant-derived origins, exhibiting humus and aromatization characteristics with high molecular weight. WEOM was rich in fulvic acid-like and humic acid-like compounds, while FA and HA contained more protein-like components. Organic material use altered WEOM, FA, and HA structures by impacting soil microbial biomass carbon (MBC) and fungal/bacterial biomass. In 0–20 cm soil layer, SOM content was mainly influenced by humus, especially the HA fraction, whereas in 20–40 cm soil layer, it was predominantly affected by WEOM. Conclusions The present study emphasizes that the application of organic materials can influence the structure of microbial communities, thereby affecting the composition of WEOM, FA, and HA, consequently influencing the organic matter content in different soil layers.

AimsThe priming effect (PE) on native soil organic matter induced by exogenous carbon addition influences soil carbon and nutrient cycling across the soil depths. Therefore, this study aimed to explore the effects of exogenous glucose-induced PE on native soil organic carbon (SOC) influenced by soil properties across soil depths, weather factors in different ecosystems and experimental variables.MethodsWe conducted a meta-analysis of 1231 experimental comparisons from 41 publications to explore the responses of native SOC to stable or radioactive carbon isotope (glucose) addition in laboratory incubation experiments representing various ecosystems and soil depths on the global scale.ResultsOverall, glucose addition had 110% positive PE on native SOC. The PE was higher in deep soil (197%) and lowest in topsoil (99%). Deep soil contains significantly lower SOC, dissolved organic carbon and microbial biomass carbon and a higher soil carbon/nitrogen ratio than topsoil. The PE positively correlated with soil carbon/nitrogen ratio and glucose addition rate but negatively correlated with microbial biomass carbon, dissolved organic carbon, SOC and incubation duration. Furthermore, PE positively related to mean annual temperature and precipitation in cropland while negatively correlated with mean annual precipitation in grassland ecosystem.ConclusionsLow soil nutrients and high carbon/nitrogen ratio is the reason for higher PE in deep soil than topsoil. Furthermore, the experimental variables and weather factors provide a framework for understanding the magnitude and direction of PE on native SOC induced by glucose addition and highlight the need for future integrated approaches of studies on PE.

Removing greenhouse gases from the atmosphere is a major challenge for today’s society. A great source of potential for greenhouse gas sequestration is beneath our feet: agricultural soil. By accumulating soil organic carbon in soil, farmers can sequester carbon dioxide and simultaneously reach soils more resilient to extreme weather events. To encourage farmers to build up humus and thus sequester carbon, some humus programmes have been developed by non-governmental organisations. In this regard, action-based reward systems are on their way to challenging the established results-based approaches. Against this background, we analyse how action-based and results-based approaches, as well as other crucial features of humus programmes, affect farmers’ willingness to participate in a humus programme. We conducted a Discrete-Choice-Experiment and analysed it using a mixed logit model. The results show that farmers have a statistically significant preference for action-based humus programmes, shorter programme durations, higher incentives, and an annual and government-funded payment. More specifically, farmer participation is twice as likely if humus formation is rewarded for action rather than results. The willingness-to-accept calculation indicates that a results-based humus programme would cost the funding agency about €20 more per ton of carbon dioxide sequestered in the soil. Above all, humus programmes with an action-based approach and annual payments would increase farmers’ willingness to participate. Our results contribute to the development of targeted humus programmes and policies to increase carbon sequestration in agricultural soils.

Soil carbon stability revisited The mechanisms underpinning soil carbon stability are complicated. The future response of soil carbon to climate change is uncertain but crucial, given that the carbon pool in soils is three times greater than that of the atmosphere. In a Perspective, Michael Schmidt and an international team of collaborators discuss how our understanding of soil carbon cycling has been changing. Rather than being mostly a function of molecular structure, as has been assumed, soil organic carbon stability is an ecosystem property. This means that it arises from complex interactions among many biotic and abiotic factors that are not fully understood. This fact must be more rigorously addressed in a new generation of experiments and soil carbon models, say Schmidt et al ., if we are to improve our attempts to understand this vital component of the Earth system. Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

Boreal forest soils function as a terrestrial net sink in the global carbon cycle. The prevailing dogma has focused on aboveground plant litter as a principal source of soil organic matter. Using ¹⁴C bomb-carbon modeling, we show that 50 to 70% of stored carbon in a chronosequence of boreal forested islands derives from roots and root-associated microorganisms. Fungal biomarkers indicate impaired degradation and preservation of fungal residues in late successional forests. Furthermore, 454 pyrosequencing of molecular barcodes, in conjunction with stable isotope analyses, highlights root-associated fungi as important regulators of ecosystem carbon dynamics. Our results suggest an alternative mechanism for the accumulation of organic matter in boreal forests during succession in the long-term absence of disturbance.

Background and aims Rhizodeposited-carbon (C) plays an important role in regulating soil C concentrations and turnover, however, the distribution of rhizodeposited-C into different soil organic carbon (SOC) pools and how regulated by nitrogen (N) fertilization still remains elusive. Methods We applied five N fertilization rates (0, 10, 20, 40, and 60 mg N kg −1 soil) to rice ( Oryza sativa L.) with continuously labeled 13 CO 2 for 18 days, to measure 13 C allocation into plant tissues and soil C fractions. Results Relative to the unfertilized controls, the ratio of 13 C in plant aboveground shoot /belowground root increased as a result of N fertilization, and the contribution of rhizodeposited-C to SOC was increased by N fertilization, presumably due to the relatively high root biomass and exudates. Also, N fertilization increased 13 C incorporation into large aggregates (0.25–2.0 mm) and the humic acid fraction. Biological C immobilization might occur and preserve rhizodeposition following high rates of N addition, which regulates rhizodeposits and C cycling, thus determining the stabilization of rhizodeposits in the different SOC pools. Conclusion Rhizodeposited-C from rice plants and its distribution within SOC pools strongly depend upon N fertilization, thus determines C sequestration potential from the rice plants.

Soil organic carbon (C) is an essential component of the global C cycle. Processes that control its composition and dynamics over large scales are not well understood. Thus, our understanding of C cycling is incomplete, which makes it difficult to predict C gains and losses due to changes in climate, land use and management. Here we show that controls on the composition of organic C, the particulate, humus and resistant fractions, and the potential vulnerability of C to decomposition across Australia are distinct, scale-dependent and variable. We used machine-learning with 5,721 topsoil measurements to show that, continentally, the climate, soil properties (for example, total nitrogen and pH) and elevation are dominant controls. However, we found that such general assessments disregard underlying region-specific controls that affect the distribution of the organic C fractions and vulnerability. This can lead to misinterpretations that prejudice our understanding of soil C processes and dynamics. Regionally, climate is mediated through interactions with soil properties, mineralogy and topography. In some regions, climate is uninfluential. These results highlight the need for regional assessments of soil C dynamics and more local parameterization of biogeochemical and Earth system models. Our analysis propounds the development of region-specific strategies for effective C management and climate change mitigation.Soil geochemistry can be more important than climate in controlling carbon storage, its composition as well as stability, but controls are distinct, scale-dependent and variable, according to an analysis of topsoil measurements across Australia.