Changes In Soil Organic Carbon Stocks Research Articles

Stability of soil organic carbon pools affected by land use and land cover changes in forests of eastern Himalayan region, India

Forests are among the largest terrestrial carbon pools that are most vulnerable to land use and land cover change (LULC). Therefore, it is essential to manage forest ecosystems to enhance soil organic carbon (SOC) pools and soil functionality. The present study was carried out to analyze C stability and change in SOC stock under different forest types in the eastern Himalayan region of India. Topsoil (0–15 and 15–30 cm) samples from six dominant forests i. e. tropical wet evergreen, montane subtropical, temperate, Quercus, bamboo, and shifting cultivation (Jhum) lands were collected and analyzed for selected soil properties and SOC stock. Active (very labile + labile), slow (less labile), and passive (non-labile) C fractions were also analyzed to determine the stability of the SOC pool under the LULC scenario. Results show that the percentage contribution of active C to total organic carbon in topsoil was highest in a temperate forest (74.1%) while lowest in a bamboo forest (48.1%). Unlike, slow C (18.4%) and passive C (26.6%) were highest in Quercus forest. Pearson correlation analysis shows significant positive relation of active and slow C pool with SOC and total nitrogen concentration. The estimates of SOC stock (0–30 cm) were significantly higher in temperate forests (132.7 Mg C ha−1). However, the conversion of natural forests to bamboo forest and jhum land reduced SOC stock by 29% and 68%, respectively. C lability index shows higher labile C in jhum land while recalcitrancy index was highest in a bamboo forest. Our study concluded that LULC change significantly altered the stability and stock of SOC in natural forests. Owing to a higher percentage of slow and passive C pools, Quercus forests play a major role in C sink management.

Long term impact of residue management on soil organic carbon stocks and nitrous oxide emissions from European croplands

Application of crop residues to agricultural fields is a significant source of the greenhouse gas nitrous oxide (N2O) and an essential factor affecting the soil organic carbon (SOC) balance. Here we present a biogeochemical modelling study assessing the impact of crop residue management on soil C stocks and N2O fluxes for EU-27 using available information on soils, management and climate and by testing various scenarios of residue management. Three biogeochemical models, i.e. CERES-EGC, LandscapeDNDC and LandscapeDNDC-MeTrx, were used in an ensemble approach on a grid of 0.25° × 0.25° spatial resolution for calculating EU-27 wide inventories of changes in SOC stocks and N2O emissions due to residue management for the years 2000–2100 using different climate change projections (RCP4.5 and RCP8.5). Our results show, that climate change poses a threat to cropping systems in Europe, resulting in potential yield declines, increased N2O emissions and loss of SOC. This highlights the need for adapting crop management to mitigate climate change impacts, e.g. by improved residue management. For a scenario with 100% residues retention and reduced tillage we calculated that in average SOC stocks may increase over 50–100 years by 19–23% under RCP8.5 and RCP4.5. However, complete retention of crop residues also resulted in an increase of soil N2O emissions by 17–30%, so that climate benefits due to increases in SOC stocks were eventually compensated by increased N2O emissions. The long-term EFN2O for residue N incorporation was 1.18% and, thus slightly higher as the 1% value used by IPCC. We conclude that residue management can be an important strategy for mitigating climate change impacts on SOC stocks, though it requires as well improvements in N management for N2O mitigation.

Continental United States may lose 1.8 petagrams of soil organic carbon under climate change by 2100

AbstractAimsHigh‐resolution information on soils’ vulnerability to climate‐induced soil organic carbon (SOC) loss can enable environmental scientists, land managers, and policy makers to develop targeted mitigation strategies. This study aims to estimate baseline and decadal changes in continental US surface SOC stocks under future emission scenarios.LocationContinental United States.Time period2014–2100.MethodsWe used recent SOC field observations (n = 6,213 sites), environmental factors (n = 32), and an ensemble machine learning (ML) approach to estimate baseline SOC stocks in surface soils across the continental United States at 100‐m spatial resolution, and decadal changes under the projected climate scenarios of Coupled Model Intercomparison Project Phase Six (CMIP6) earth system models (ESMs).ResultsBaseline SOC projections from ML approaches captured more than 50% of variability in SOC observations, whereas ESMs represented only 6–16% of observed SOC variability. ML estimates showed a mean total loss of 1.8 Pg C from US surface soils under the high‐emission scenario by 2100, whereas ESMs showed no significant change in SOC stocks with wide variation among ESMs. Both ML and ESM predictions agree on the direction of SOC change (net emissions or sequestration) across 46–51% of continental US land area. These differences are attributable to the high‐resolution site‐specific data used in the ML models compared to the relatively coarse grid represented in CMIP6 ESMs.Main conclusionsOur high‐resolution estimates of baseline SOC stocks, identification of key environmental controllers, and projection of SOC changes from US land cover types under future climate scenarios suggest the need for high‐resolution simulations of SOC in ESMs to represent the heterogeneity of SOC. We found that the SOC change is sensitive to key soil related factors (e.g. soil drainage and soil order) that have not been historically considered as input parameters in ESMs, because currently more than 95% variability in the SOC of CMIP6 ESMs is controlled by net primary productivity, temperature, and precipitation. Using additional environmental factors to estimate the baseline SOC stocks and predict the future trajectory of SOC change can provide more accurate results.

Changes in organic matter contents and carbon stocks in Dutch soils, 1998–2018

Changes in soil organic matter (SOM) content and soil organic carbon (SOC) stock in the 0–30 cm and 30–100 cm soil layers between 1998 and 2018 in the Netherlands were estimated by repeated sampling of 1152 locations in the Soil Sampling Programme (SSP). These locations were selected following a stratified simple random sampling design. We discuss various barriers we met: restricted accuracy of information on soil bulk density, uncertainties due to positional errors, differences in sampling support, and changes in laboratory analysis methods since 1998. Domains of interest such as mineral soils were defined either on the basis of the stratification of the SSP sample (geomatching) or on the basis of soil profiles observed at the selected locations (classmatching). The mean SOM content changed significantly in the 30–100 cm layer (-17.68 gkg-1) in the entire area of interest (non-built-up area in the Netherlands) between 1998 and 2018 (at a 5% significance level). A decrease in SOM content between 1998 and 2018 could be shown for the 0–30 cm layer in mineral soils under cropland if classmatching was applied (at a 5% significance level), but no change could be shown in this layer in the remaining domains of interest, whether geomatching or classmatching were applied. For the 30–100 cm layer in mineral soils, significant changes in mean SOM content were shown by classmatching: −8.59 gkg-1 under cropland and −4.75 gkg-1 under grassland. The calculations indicate that SOC stocks decreased between 1998 and 2018 in both the 0–30 cm and the 30–100 cm layer of mineral soils under both cropland and grassland. The accuracy of the bulk density data needs to be improved in future measurements to increase the accuracy of calculations of the SOC stock changes.

Land conversion from annual to perennial crops: A win-win strategy for biomass yield and soil organic carbon and total nitrogen sequestration

How much can we increase biomass yield by promoting land conversion from annual to perennial crops? Will increased biomass extraction for biorefineries reduce soil organic carbon (SOC) and total nitrogen (TN) stock? Which cropping system is more stable for biomass production over time? To our knowledge, no study has concurrently investigated the effects of land conversion from annual to perennial crops on biomass yield, yield stability, and changes in SOC and TN stock, which limits the understanding and application of sustainable agroecosystems producing biomass for biorefineries. Based on five-year continuous observations in central Jutland Denmark, our results showed that perennial crops significantly increased biomass yield by 19% and yield stability by 88% compared to annual crops. Perennial crops significantly increased SOC content by 4% and SOC stock by 11% at 0–100 cm depth across the five years. The opposite responses of SOC content and stock under annual and perennial crops led to even more significant differences between the crop types. Perennial crops had no effect on soil TN content and increased soil TN stock to one meter depth by 22%, whereas continuous annual crops had no effect on it. Neither annual nor perennial crops had effects on SOC and TN stock when estimated based on equivalent soil mass because the soil density increased under perennial crops. Our results showed that changes in SOC and TN stock between annual and perennial crops varied with the specific calculating methods (fixed depth/equivalent mass), thus the selected methods should be clearly defined in the future research. Increases in SOC content at one meter depth were positively correlated with biomass yield and yield stability, suggesting a win-win strategy for climate mitigation and food security. Altogether, our results highlight the potential to redesign the current cropping system for sustainable intensification by selecting proper perennial crops for green biorefineries.

Topsoil carbon sequestration of vegetation restoration on the Loess Plateau

Vegetation restoration plays an important role in enhancing soil organic carbon (SOC) sequestration. However, there are diverse types of vegetation restoration with different SOC sequestration rates. Understanding the dynamic of SOC at topsoil (0–20 cm) and potential problems of the different types (i.e., woodlands, shrub lands, artificial grasslands, orchards, and abandoned lands) are important for future sustainable development. We surveyed 73 peer-reviewed studies conducted on the Chinese Loess Plateau from 2000 to 2019. The relative change in SOC stock under shrub lands, woodlands, and abandoned lands performed significantly and positively related to restoration time (P < 0.001). The rate was highest for shrub lands (0.55 ± 0.45 t ha−1 yr−1) compared to that of other restoration types. The Robinia pseudoacacia, a typical N-fixers, sequestrate more SOC (3.84% yr−1) than other tree species (1.18% yr−1). Orchards and artificial grasslands, however, were based on the relatively weak relations between restoration age and SOC stock with the low efficiency of SOC stock change (19.0 ± 32.1% and 20.2 ± 35.2% respectively overall time). The restoration age, initial SOC stock, and temperature significantly influenced the relative change in SOC stock (P < 0.001). In addition, the shrub lands remained inert to the temperature and precipitation (P > 0.05), indicating its wide adaptability on the Loess Plateau. We conclude that restoration types and environmental factors control SOC dynamic, and must be considered for the vegetation restoration types.

EPIC model simulation to assess effective agro-ecological practices for climate change mitigation and adaptation in organic vegetable system

Mediterranean agriculture is markedly threatened by climate change and extreme events (drought and flooding). For the first time, the EPIC model was used in a long-term organic vegetable field experiment to evaluate the performance of agro-ecological practices, as adaptation and mitigation measures to cope with climate change in Southern Italy. These practices were a soil hydraulic arrangement (consisting of ridges and flat strips) combined with crop rotation (winter and summer cash crops), organic fertilization (poultry manure vs. no fertilization), and cover crops (pure or in mixture vs. no cover) managed as living mulch, green manure, or flattened by roller crimper. Seven treatments were selected for the simulation procedure. EPIC was calibrated and validated using measured crop yield and soil organic carbon stock values. The statistical metrics of EPIC showed r to be between 0.96 and 0.97, the Nash–Sutcliffe model efficiency between 0.54 and 0.94, and the relative root mean square error between 2 and 18%. Then, the model was run under baseline current climate (1985–2014) and near-future climate change (2015–2044) scenarios. Climate change increased both microbial respiration and nitrate leaching compared to the baseline, while soil organic carbon stock change and nitrous oxide emissions were mainly influenced by agro-ecological practices. Cover crop management could be an effective solution to limit negative climate effects, since it allowed improving summer cash crop yield (32%) and soil organic carbon stock change (2%), and reducing nitrogen losses (–34%), as compared to the no-cover-crop system. Finally, under climate change, green manure increased microbial respiration (5%) and reduced nitrogen losses (− 19%), compared to roller crimper flattening. Our findings indicated that the tested agro-ecological practices contribute to re-designing new climate change-resilient vegetable systems, by involving the stakeholders in promoting a co-innovation and co-research knowledge platform and fine-tuning agro-ecological practices in a wider range of environments.

A robust initialization method for accurate soil organic carbon simulations

Abstract. Changes in soil organic carbon (SOC) stocks are a major source of uncertainty for the evolution of atmospheric CO2 concentration during the 21st century. They are usually simulated by models dividing SOC into conceptual pools with contrasted turnover times. The lack of reliable methods to initialize these models, by correctly distributing soil carbon amongst their kinetic pools, strongly limits the accuracy of their simulations. Here, we demonstrate that PARTYSOC, a machine-learning model based on Rock-Eval® thermal analysis, optimally partitions the active- and stable-SOC pools of AMG, a simple and well-validated SOC dynamics model, accounting for effects of soil management history. Furthermore, we found that initializing the SOC pool sizes of AMG using machine learning strongly improves its accuracy when reproducing the observed SOC dynamics in nine independent French long-term agricultural experiments. Our results indicate that multi-compartmental models of SOC dynamics combined with a robust initialization can simulate observed SOC stock changes with excellent precision. We recommend exploring their potential before a new generation of models of greater complexity becomes operational. The approach proposed here can be easily implemented on soil monitoring networks, paving the way towards precise predictions of SOC stock changes over the next decades.

Higher carbon sequestration on Swedish dairy farms compared with other farm types as revealed by national soil inventories

Small changes in the large stock of soil organic carbon (SOC) can have a substantial influence on the climate impact of agriculture. We used information from a Swedish soil monitoring program, in combination with farm census data, to analyze decadal SOC concentrations and SOC stock changes on dairy farms compared with other farm types, and to quantify the climate impact of these changes on dairy farms. Soil monitoring data included topsoil samples from two inventories on 159 dairy farms, 86 beef farms, 318 arable farms, and 13 pig farms, taken at the same locations in 2001–2007 and 2011–2017. Concentrations of SOC on dairy farms (3.0%) were significantly higher than on arable farms (2.3%) and pig farms (2.4%), but not significantly different from beef farms (3.1%). SOC concentration was correlated with proportion of ley at farm scale. SOC stocks in the upper 20 cm increased significantly on dairy, beef, and arable farms, by 0.38, 0.14, and 0.21 Mg C ha−1 year−1, respectively, between 2001–2007 and 2011–2017. For dairy farms, this corresponded to −1.4 Mg CO2 ha−1 and approximately −0.22 kg CO2 kg−1 energy-corrected milk, demonstrating that SOC changes could have a substantial influence on the climate footprint of milk.

A Meta-Analysis of the Soil Organic Carbon Stock Change Following Perennialization

A Meta-Analysis of the Soil Organic Carbon Stock Change Following Perennialization

Mudanças no estoque de carbono orgânico e produtividade de culturas em solo arenoso tropical sob sistemas de produção de grãos-algodão em sequeiro na Bahia, Brasil

ABSTRACT Most studies about soil organic carbon stock changes in the Cerrado (Brazilian Savanna) biome are either related to field data collected in clayey Ferralsols or different land uses, as if they were in equilibrium. This study aimed to evaluate the effect of tillage systems and crop sequences on the soil organic carbon stock and crop yield, in a sandy Ferralsol from Bahia, Brazil. The experimental design was randomized blocks, with four replicates. Soil samples were collected after fve years of cotton, soybean and maize monocropping under heavy disk harrow and leveling harrow (conventional tillage), and of crop rotation of cotton, soybean and maize with green manure or cover crop (no-tillage). Additional samples were collected from a non-cultivated site (Neotropical Savanna, Cerrado sensu stricto). Soil conservation practices such as no-tillage and crop rotation with cover crop and green manure favored the soil organic carbon stock at the 0-40 cm layer, with the highest values reaching 36.03 Mg ha−1. The accrued soil carbon stock under conventional tillage and monoculture of cotton, maize and soybean was lower than under no-tillage, which ranged from 30.9 to 54.9 %, with the soil organic carbon stock increasing at the annual rate of 2.36 Mg ha−1 during fve years. The no-tillage, with the soybean-maize-cotton rotation, in combination with cover crop and green manure, increased the cotton and soybean yields, with a simultaneous organic carbon accumulation in the sandy soil.

Soil organic carbon content and stock change after half a century of intensive cultivation in a chernozem area

Soil organic carbon (SOC) is a significant soil parameter controlling soil quality and productivity and also playing an essential role in the global carbon cycle. Assessment of long-term SOC content and stocks changes is only possible by comparing historical and present data. The Czech Republic holds a national database of agricultural soils completed during the 1960s, which we used to assess SOC changes. SOC content and stock changes were detected after more than 50 years of intensive cultivation in a rolling chernozem landscape prone to soil erosion by re-sampling soil profiles from the 1960s and assessing these changes in relation to local topography. Each re-sampled soil profile was classified based on its position within the terrain, into one of three distinct slope positions namely shoulder slope (SH), backslope (BS), and foot slope (FS) which refers to a predisposition to soil erosion (SH, BS) or deposition (FS). Despite previous studies reporting SOC content decline over the past several decades, our results showed an increase in SOC content in all slope positions, being the most pronounced at FS position. However, median value for the SOC stock significantly decreased at SH positions primarily due to intensive erosion (decreased by 2.82 kg·m−2). At the FS positions, the median value for the SOC stock increased but not significantly (increased by 5.51 kg·m−2). Changes in the SOC stock were primarily driven by changes in the topsoil depth, which significantly decreased at the SH positions by 22 cm; the opposite result was found for the FS position. The local topography as a driver of SOC stock changes was further supported by the significant correlation between SOC stock changes and topographical attributes (predominantly with Multiresolution Valley Bottom Flatness index, Topographic position index or Topographic wetness index) showing increasing SOC stocks in terrain depressions or valley bottoms due to soil accumulation. We concluded that soil erosion is a dominant process in our study area, explaining the long-term changes in SOC stock.

Analysis of the consequences of land-use changes and soil types on organic carbon storage in the Tarim River Basin from 2000 to 2020

With fast development of industry and agriculture in last two decades, land use changed greatly on specific soil types of intrinsic low quality with C loss potential and necessitates avoiding. Although researchers studied the effect of land-use changes on soil carbon storage, that on some soil types had rarely been reported, which led to relatively more C loss. We explored the impact of land-use changes and soil types on soil organic carbon (SOC) sequestration in the top 30 cm in the Tarim River Basin (the second largest inland river in the world) from 2000 to 2020. The land-use images with a one-kilometer spatial resolution and soil data from the Harmonized World Soil Database were analysed. The groundwater levels were monitored by 11 wells along the river from 2012 to 2017. Land-use changes were dominated by increases in the areas of cultivated land (1843–4099 km2) and woodland (5055–5433 km2) and decreases in grassland area ( 19076–12634 km2). The increase in cultivated land area was acquired from grassland (54%), woodland (32%) and unused land (14%), which was dominated by Phaeozems, Solonchaks and Fluvisols (84%). The converted land use to woodland was dominated by Fluvisols, Phaeozems, Arenosols and Solonchaks (98%). The converted land use from grassland to other land-use types was dominated by Arenosols, Fluvisols and Phaeozems (85%). The SOC was reduced by 9.83 Tg (+8.04 in cultivated land, +0.06 in woodland, −17.93 in grassland). The SOC stock change efficiency (SOCE kg C m−2) was SOC change divided by area change. The increase in SOC (Tg) of cultivated land was 5.04 from grassland (SOCE 3.76) and 2.9 from woodland (SOCE 3.68). The SOC of woodland increased by 8.66 Tg at cost of losing grassland (SOCE 3.35). Moreover, land-use changes affected local ecological environment. The cultivated land along the river increased 298 km2, and the desertification advanced towards oasis by decreasing 950 km2 of grassland in transition zone. The average groundwater table increased in the upstream (−3.12 to −2.33 m) and midstream regions (−1.84 to −1.71 m) monthly from 2012 to 2017 and in the downstream region (−7 to −2.84 m) annually from 2009 to 2017. This was attributed to expanded cultivated land and salt-washing cultivation on Solonchaks. In conclusion, the land-use conversion from grassland to woodland and cultivated land, mainly for Fluvisols, Phaeozems and Solonchaks, caused negative SOC storage, especially in riverbanks and oasis-desert transition zones facing climate change.

Assessing Soil Organic Carbon Stock Dynamics under Future Climate Change Scenarios in the Middle Qilian Mountains

Soil organic carbon (SOC) simply cannot be managed if its amounts, changes and locations are not well known. Thus, evaluations of the spatio-temporal dynamics of SOC stock under future climate change are crucial for the adaptive management of regional carbon sequestration. Here, we evaluated the dynamics of SOC stock to a 60 cm depth in the middle Qilian Mountains (1755–5051 m a.s.l.) by combining systematic measurements from 138 sampling sites with a machine learning model. Our results reveal that the combination of systematic measurements with the machine learning model allowed spatially explicit estimates of SOC change to be made. The average SOC stock in the middle Qilian Mountains was expected to decrease under future climate change, while the size and direction of SOC stock changes seemed to be elevation-dependent. Specifically, in comparison with the 2000s, the mean annual precipitation was projected to increase by 18.37, 19.80 and 30.80 mm, and the mean annual temperature was projected to increase by 1.9, 2.4 and 2.9 °C under the Representative Concentration Pathway (RCP) 2.6 (low-emissions pathway), RCP4.5 (low-to-moderate-emissions pathway), and RCP8.5 (high-emissions pathway) scenarios by the 2050s, respectively. Accordingly, the area-weighted SOC stock and total storage for the whole study area were estimated to decrease by 0.43, 0.63 and 1.01 kg m–2 and 4.55, 6.66 and 10.62 Tg under the RCP2.6, RCP4.5 and RCP8.5 scenarios, respectively. In addition, the mid-elevation zones (3100–3900 m), especially the subalpine shrub-meadow Mollic Leptosols, were projected to experience the most intense carbon loss. However, the higher elevation zones (&gt;3900 m), especially the alpine desert zone, were characterized by significant carbon accumulation. As for the low-elevation zones (&lt;2900 m), SOC was projected to be less varied under future climate change scenarios. Thus, the mid-elevation zones, especially the subalpine shrub-meadows and Mollic Leptosols, should be given priority in terms of reducing CO2 emissions in the Qilian Mountains.

Soil Organic Carbon Stocks in Afforested Agricultural Land in Lithuanian Hemiboreal Forest Zone

In the context of the specificity of soil organic carbon (SOC) storage in afforested land, nutrient-poor Arenosols and nutrient-rich Luvisols after afforestation with coniferous and deciduous tree species were studied in comparison to the same soils of croplands and grasslands. This study analysed the changes in SOC stock up to 30 years after afforestation of agricultural land in Lithuania, representing the cool temperate moist climate region of Europe. The SOC stocks were evaluated by applying the paired-site design. The mean mass and SOC stocks of the forest floor in afforested Arenosols increased more than in Luvisols. Almost twice as much forest floor mass was observed in coniferous than in deciduous stands 2–3 decades after afforestation. The mean bulk density of fine (&lt;2 mm) soil in the 0–30 cm mineral topsoil layer of croplands was higher than in afforested sites and grasslands. The clear decreasing trend in mean bulk density due to forest stand age with the lowest values in the 21–30-year-old stands was found in afforested Luvisols. In contrast, the SOC concentrations in the 0–30 cm mineral topsoil layer, especially in Luvisols afforested with coniferous species, showed an increasing trend due to the influence of stand age. The mean SOC values in the 0–30 cm mineral topsoil layer of Arenosols and Luvisols during the 30 years after afforestation did not significantly differ from the adjacent croplands or grasslands. The mean SOC stock slightly increased with the forest stand age in Luvisols; however, the highest mean SOC stock was detected in the grasslands. In the Arenosols, there was higher SOC accumulation in the forest floor with increasing stand age than in the Luvisols, while the proportion of SOC stocks in mineral topsoil layers was similar and more comparable to grasslands. These findings suggest encouragement of afforestation of former agricultural land under the current climate and soil characteristics in the region, but the conversion of perennial grasslands to forest land should be done with caution.

Soil organic carbon dynamics from agricultural management practices under climate change

Abstract. Sequestration of soil organic carbon (SOC) on cropland has been proposed as a climate change mitigation strategy to reduce global greenhouse gas (GHG) concentrations in the atmosphere, which in particular is needed to achieve the targets proposed in the Paris Agreement to limit the increase in atmospheric temperature to well below 2 ∘C. We analyze the historical evolution and future development of cropland SOC using the global process-based biophysical model LPJmL, which was recently extended by a detailed representation of tillage practices and residue management (version 5.0-tillage2). We find that model results for historical global estimates for SOC stocks are at the upper end of available literature, with ∼2650 Pg C of SOC stored globally in the year 2018, ∼170 Pg C of which is stored in cropland soils. In future projections, assuming no further changes in current cropland patterns and under four different management assumptions with two different climate forcings, RCP2.6 and RCP8.5, results suggest that agricultural SOC stocks decline in all scenarios, as the decomposition of SOC outweighs the increase in carbon inputs into the soil from altered management practices. Different climate change scenarios, as well as assumptions on tillage management, play a minor role in explaining differences in SOC stocks. The choice of tillage practice explains between 0.2 % and 1.3 % of total cropland SOC stock change in the year 2100. Future dynamics in cropland SOC are most strongly controlled by residue management: whether residues are left on the field or harvested. We find that on current cropland, global cropland SOC stocks decline until the end of the century by only 1.0 % to 1.4 % if residue retention management systems are generally applied and by 26.7 % to 27.3 % in the case of residue harvest. For different climatic regions, increases in cropland SOC can only be found for tropical dry, warm temperate moist, and warm temperate dry regions in management systems that retain residues.

Spatial and temporal dynamics of soil organic carbon stock and carbon sequestration affected by major land-use conversions in Northwestern highlands of Ethiopia

Soil organic carbon (SOC) is the major component of the terrestrial carbon (C) budget, a key indicator of environmental sustainability. So, estimating SOC stock and soil carbon (C) sequestration dynamics is important for evidence-based and carbon-conscious decisions. Quantification of SOC stock and soil C sequestration affected by land-use changes (LUCs) have received much attention in addressing food and climate security. This study aims to estimate the dynamics of SOC stock, soil C sequestration and associated soil parameters affected by major LUCs from 2012 to 2021 in Awi highlands of Amhara Regional State of Ethiopia. The study area has experienced dramatic LUC, particularly plantation and growing of Acacia decurrens (J.C. Wendl.) tree followed by recurrent deforestation and then cropping and back to the plantation. The study quantified spatial and temporal dynamics of SOC stock, soil C sequestration and associated changes affected by the LUCs. A total of 22 topsoil (0–20 cm) legacy data was obtained from the Ethiopian Soil Information System (EthiSIS) database of 2012. The same number of samples were collected at the same locations in 2021 by using the same sampling procedure as that of 2012. In addition, the same number of core samples were collected in 2021 for bulk density analysis. To estimate the unmeasured bulk density of legacy data, we applied a pedotransfer function. We used empirical equations and basic statistics to assess changes in SOC stock and C sequestration rate between the two periods. Statistically significant variation (P < 0.01) in SOC stock and C sequestration was observed between the two periods. LUC from acacia plantation to croplands caused a decline of SOC stock by −30.16%, and it also caused the decline of total nitrogen stock, available phosphorus, cation exchange capacity (CEC). However, the reverse LUC caused an increase in SOC by 27.74% and the abovementioned soil parameters. LUC from plantation forest to cropland caused emission of 8.3 tons of CO2 year−1. Generally, overall LUCs caused the net negative change in SOC stock by (−2.42 %) and associated soil parameters in the last ten years. Our study provides evidence that overall LUCs in the current study site caused a decline in SOC stock, along with associated soil parameters with carbon emitted to the atmosphere. Hence, sustainable land-use management options which can offset losses in SOC stock should be implemented soon.

The effect of soil and water conservation measures on soil organic carbon in a typical small watershed in the Mollisol region of Northeast China

Soil organic carbon (SOC) content is one of the most important indicators of soil sustainability. Understanding how soil and water conservation (SWC) measures affect the SOC stock is important for the protection of soil and water quality. In the present study, the impacts of SWC measures on the SOC stock change in a typical small watershed in the Mollisol region of Northeast China were investigated using a grid soil sampling scheme. A total of 292 soil samples were collected in the same locations in 2005 and 2016. The results indicated that the average annual increase rate of SOC was 5.43‰. The equivalent soil mass (ESM) method indicated that the change rate of the SOC stock significantly increased from 2005 to 2016, with an average annual increase rate of 3.33‰. The SOC stock change was significantly affected by the SWC measures, the initial SOC content, and the interaction between the SWC measures and the initial SOC content. Furthermore, grassland had a greater change rate of the SOC stock than the other SWC measures (P < 0.05). As the initial SOC content increased, the change rate of the SOC stock significantly decreased (P < 0.05). The change rate of the SOC stock in forestland significantly increased with an increase in the initial SOC level, but the opposite trend was found in the grassland and terrace (P < 0.05). In addition, soil erosion occurred on the upper and middle slopes, and soil deposition occurred on the foot slope in the typical sloping farmland (P < 0.05); forestland had better control effect on soil erosion than farmland. Our findings provide science-based recommendations for enhancing SOC storage in agricultural sites by implementing SWC measures.

Modelling and mapping soil organic carbon stocks under future climate change in south-eastern Australia

Soil organic carbon (SOC) plays a key role in the sequestration of carbon that could otherwise be warming the atmosphere. Climate change including increased temperature and changed rainfall will greatly impact the global SOC cycle. There are still significant gaps in our knowledge of the size of the global SOC pool and how future climate will affect SOC stocks and flows in many parts of the world, including Australia. In this study, we used SOC data in a Digital Soil Mapping framework to predict current and future SOC stocks across the state of New South Wales (NSW) in south-eastern Australia. In the first phase of the study we estimated the current SOC stock using multiple linear regression (MLR) and random forest (RF) modelling, and in the second phase we projected the change of SOC stocks in the near future (2050s) and far future (2090s) under two Shared Socio-economic Pathways (SSPs) scenarios based on 25 global climate models (GCMs) from the Coupled Model Inter-comparison Project Phase 6 (CMIP6). Our spatial modelling showed that estimated current SOC stocks in NSW decreased from east to west. Multi-GCM ensemble means suggested SOC stocks would decrease by 7.6–12.9% under SSP2-4.5 and 9.1–20.9% under SSP5-8.5 across NSW under future climate. The extent of change in SOC stocks varied spatially with the largest mean decrease of SOC stocks occurring in the North Coast and South East (alpine) regions of NSW. Our findings can support decision-making in land management and climate change mitigation strategies in NSW at the regional level. Furthermore, the modelling methods can be applied to other areas where edaphic and landscape properties, land use, and climate data are available.

Challenges in using soil carbon modelling in LCA of agricultural products\u2014the devil is in the detail

PurposeCurrently, there is no consensus on how the impacts of land use on the soil organic carbon (SOC) stocks would be best quantified within life cycle assessments (LCA) of agricultural products. The impacts of different decisions were tested within a model-based assessment of soil carbon changes on the life cycle global warming impact for spring wheat produced in two example regions in Finland (Southwest Finland and Northern Savonia) on mineral fields.MethodsGlobal warming impact for spring wheat was assessed, including CO2 emissions due to the SOC change. The SOC change assessment was made with the soil carbon model Yasso07. The effects of assumptions on land use history were tested, i.e. the initialisation of the model and time horizon of the analysis (20 or 100 years) on the SOC change estimates. Other greenhouse gas emissions contributing to the global warming impact of spring wheat production were assessed using general LCA methodology taking into account the greenhouse gas emissions caused by the production of input materials and fuels, as well as direct and indirect N2O emissions from the soil due to fertilising and the decomposition of crop residues and organic matter, nitrogen leaching and volatilisation and lime application.Results and discussionThe selection of the model initialisation method and timeframe remarkably affected the SOC change estimates. The global warming impact of wheat production, without accounting for SOC changes, was 0.68 and 0.89 kg CO2-eq/kg yield in Southwest Finland and Northern Savonia, respectively. The impact of SOC stock changes on the total global warming impact varied from –4 to 5% in Southwest Finland and from 5 to 21% in Northern Savonia, depending on the assumptions used to initialise the model or the timeframe applied in the analysis. Adding a cover crop as a means to increase the SOC stock removed between –67 and –26% of the total global warming impact in both regions.ConclusionsIt is essential that all the decisions made in the analysis are transparently reported and communicated. The choice of assumptions regarding the reference state, model initialisation and time horizon of the assessment period should be made based on the scope and goal definition of the LCA study.