Variability Of Soil Organic Carbon Research Articles

Synergistic Use of Multi-Temporal Radar and Optical Remote Sensing for Soil Organic Carbon Prediction

Exploring soil organic carbon (SOC) mapping is crucial for addressing critical challenges in environmental sustainability and food security. This study evaluates the suitability of the synergistic use of multi-temporal and high-resolution radar and optical remote sensing data for SOC prediction in the Kaffrine region of Senegal, covering over 1.1 million hectares. For this purpose, various scenarios were developed: Scenario 1 (Sentinel-1 data), Scenario 2 (Sentinel-2 data), Scenario 3 (Sentinel-1 and Sentinel-2 combination), Scenario 4 (topographic features), and Scenario 5 (Sentinel-1 and -2 with topographic features). The findings from comparing three different algorithms (Random Forest (RF), XGBoost, and Support Vector Regression (SVR)) with 671 soil samples for training and 281 samples for model evaluation highlight that RF outperformed the other models across different scenarios. Moreover, using Sentinel-2 data alone yielded better results than using only Sentinel-1 data. However, combining Sentinel-1 and Sentinel-2 data (Scenario 3) further improved the performance by 6% to 11%. Including topographic features (Scenario 5) achieved the highest accuracy, reaching an R2 of 0.7, an RMSE of 0.012%, and an RPIQ of 5.754 for the RF model. Applying the RF and XGBoost models under Scenario 5 for SOC mapping showed that both models tended to predict low SOC values across the study area, which is consistent with the predominantly low SOC content observed in most of the training data. This limitation constrains the ability of ML models to capture the full range of SOC variability, particularly for less frequent, slightly higher SOC values.

Variations in Soil Organic Carbon after Farmland Conversion to Apple Orchard

The Chinese Loess Plateau has undergone extensive revegetation to restore degraded land and enhance carbon sequestration. However, soil organic carbon (SOC) sequestrated in the soil profiles of deep-rooted plants has not been fully studied. Here, we investigated the SOC within a 0–23 m profile in farmlands and apple orchards converted from farmlands with different ages (A5, <5 years; A10, ~10 years; A15, ~15 years; A20, >20 years) and the controlling factors on three loess tablelands (Changwu, Qingyang, and Luochuan). The results show that SOC stocks among farmlands and orchards showed no significant difference (p = 0.88); however, SOC stocks showed a trend with tree ages, i.e., a decrease for A5 and A10 but an increase for A15 and A20. For the vertical variability, the SOC stock was the highest within 0–1 m, regardless of the standing age; however, the SOC stock in this layer only accounted for 8.8% of the total SOC stock (97.93 ± 9.18 kg m−2). Climate accounted for 82% of the variations and controlled the changes in SOC in the 0–1 m range, while soil texture dominated the SOC in the soil below 1 m, accounting for 57% of the SOC variations. The variations in SOC in the thick, unsaturated zones provide implications for future land use management and the sustainability of apple orchards in arid regions.

Three-dimensional spatiotemporal variation of soil organic carbon and its influencing factors at the basin scale

The variability of soil organic carbon (SOC) extends across three dimensions. However, quantitative analyses of the factors influencing spatiotemporal variations of SOC at continuous depths have been scarce. This study leverages legacy data from two soil surveys conducted in the Dongting Lake Basin during the 1980s and the 2010s, employing Random Forest models to generate three-dimensional SOC maps. Through correlation analysis and permutation importance, we identified the primary factors driving temporal and spatial changes of SOC. The results showed that in the 2010s, SOC storage up to a depth of 1 m in the Dongting Lake Basin was approximately 2.95 Pg, increasing at an average rate of 0.0047 Pg C per year since the 1980s. Regions with higher average SOC contents were predominantly found in the western, southern, and eastern parts of the basin, despite significant losses over the 30-year period. In contrast, the central and northern areas, which initially had lower SOC contents in the 1980s, exhibited increases by the 2010s. Soil depth was the most influential predictor of SOC patterns in both the 1980s and 2010s. Meanwhile, relief and organism factors were primarily responsible for spatial variations in SOC, with the influence of organism factors diminishing by the 2010s. The temporal variations of SOC were chiefly attributed to changes in soil conservation practices, extreme precipitation events, and grain production. Consequently, it is imperative to prioritize ecological restoration and conservation tillage practices to mitigate the impacts of extreme weather conditions and safeguard food security.

Multivariate and scale-dependent controls of deep soil carbon after afforestation in a typical loess-covered region

Afforestation is beneficial to improving soil carbon pools. However, due to the lack of deep databases, the variations in soil carbon and the combined effects of multiple factors after afforestation have yet to be adequately explored in >1 m deep soils, especially in areas with deep-rooted plants and thick vadose zones. This study examined the multivariate controls of soil organic carbon (SOC) and inorganic carbon (SIC) in 0–18 m deep under farmland, grassland, willow, and poplar in loess deposits. The novelty of this study is that the factors concurrently affecting deep soil carbon were investigated by multiwavelet coherence and structural equation models. On average, the SOC density (53.1 ± 5.0 kg m−2) was only 12% of SIC density (425.4 ± 13.8 kg m−2), with depth-dependent variations under different land use types. In the soil profiles, the variations in SOC were more obvious in the 0–6 m layer, while SIC variations were mainly observed in the 6–12 m layer. Compared with farmland (SOC: 17.0 kg m−2; SIC: 122.9 kg m−2), the plantation of deciduous poplar (SOC: 28.5 kg m−2; SIC: 144.2 kg m−2) increased the SOC and SIC density within the 0–6 m layer (p < 0.05), but grassland and evergreen willow impacted SOC and SIC density insignificantly. The wavelet coherence analysis showed that, at the large scale (>4 m), SOC and SIC intensities were affected by total nitrogen-magnetic susceptibility and magnetic susceptibility-water content, respectively. The structural equation model further identified that SOC density was directly controlled by total nitrogen (path coefficient = 0.64) and indirectly affected by magnetic susceptibility (path coefficient = 0.36). Further, SOC stimulated the SIC deposition by improving water conservation and electrical conductivity. This study provides new insights into afforestation-induced deep carbon cycles, which have crucial implications for forest management and enhancing ecosystem sustainability in arid regions.

The effects of elevated CO2 and temperature on soil organic carbon and total nitrogen contents and mineralization in the 0 to 50 cm paddy soil layer were masked by different land use history

Global warming can accelerate soil organic matter (SOM) decomposition resulting in faster carbon loss and positive climate-C feedback. Previous studies on response of SOM decomposition to climate change mainly focus on plow soil layer. However, the effects of elevated CO2 and soil warming on soil organic carbon (SOC) and total nitrogen (TN) contents and mineralization are rarely studied in subsoil layer. In this study, soil samples were collected from the 0–50-cm paddy soil layer of the Tsukuba free-air CO2 enrichment experimental site with elevated CO2 (+200 ppm) and soil warming (+2 °C), Japan, after 5-year rice growth season. The amounts of SOC, TN, δ13C, and δ15N were analyzed. A 4-week anaerobic incubation experiment was conducted to measure C decomposition and N mineralization potentials. Due to the intrinsic variation in SOC and TN contents in soil layers and fields, the effects of elevated CO2 and soil warming on C decomposition and N mineralization potentials could not be determined here. However, the effect of elevated CO2 on δ13C was only found in 0‒10-cm soil layer. In the 0–50-cm soil profiles, significant correlations were observed among SOC and TN, δ13C and δ15N, decomposed C and mineralized N, and δ13C in decomposed C. The variables associated with soil C and N pools, and dynamics showed large spatial heterogeneity within paddy field, due to variation in the original land use history. Therefore, great caution should be exercised when evaluating the effects of elevated CO2 and temperature on SOM decomposition and sequestration in paddy soil profiles.

Variability of soil organic carbon and nutrient content across land uses and agriculturally induced land use changes in the forest-savanna transition zone of Cameroon

Data expressing the effects of land use change on soil attributes is still very scarce in Cameroon as in most of Africa. In this regard, this study aimed to assess soil organic carbon (OC), nitrogen (N), phosphorus (P), and potassium (K) content across land uses and agricultural-induced land use changes in the forest-savanna transition zone of Cameroon. Nine land uses were identified in the study area showing five directions of land use changes namely the change from the native forest to cocoa agroforestry, native savannah to cocoa agroforestry, native savannah to cropland, savannah fallow to cropland, and transition zone fallow to cropland. The soil was sampled at 0–10 cm (upper layer) and 10–30 cm (lower layer) depths in three replicates for each land use and analyzed for physicochemical properties. There were significant differences across the land uses for OC (p < 0.02), N (p < 0.01), C/N (p < 0.01), pH (p < 0.02), soil organic carbon stocks (SOCS) (p < 0.01), and soil nitrogen stocks (SNS) (p < 0.01), with a relatively higher magnitude in the upper soil layer. Higher magnitudes of OC (26.1 to 22.5 g kg−1), N (2.5 to 1.6 g kg−1), SOCS (32.1 to 27.8 Mg ha−1), and SNS (2.9 to1.9 Mg ha−1) were observed in native lands and cocoa agroforestry with the highest in the native forest and the forest-based cocoa agroforestry. Meanwhile, the effect of land use change on soil properties was mainly significant in the change from native savannah to croplands at p < 0.05 for OC, N, SOCS, and SNS, and p < 0.02 for P. Therefore, agroforestry is an alternative to enhance the ecological resilience of lands affected by land use changes.

Negative correlation between soil salinity and soil organic carbon variability

Soil organic carbon (SOC) is vital for terrestrial ecosystems, affecting biogeochemical processes, and soil health. It is known that soil salinity impacts SOC content, yet the specific direction and magnitude of SOC variability in relation to soil salinity remain poorly understood. Analyzing 43,459 mineral soil samples (SOC < 150 g kg-1) collected across different land covers since 1992, we approximate a soil salinity increase from 1 to 5 dS m-1 in croplands would be associated with a decline in mineral soils SOC from 0.14 g kg-1 above the mean predicted SOC ([Formula: see text] = 18.47 g kg-1) to 0.46 g kg-1 below [Formula: see text] (~-430%), while for noncroplands, such decline is sharper, from 0.96 above [Formula: see text] = 35.96 g kg-1 to 4.99 below [Formula: see text] (~-620%). Although salinity's significance in explaining SOC variability is minor (<6%), we estimate a one SD increase in salinity of topsoil samples (0 to 7 cm) correlates with respective [Formula: see text] declines of ~4.4% and ~9.26%, relative to [Formula: see text] and [Formula: see text]. The [Formula: see text] decline in croplands is greatest in vegetation/cropland mosaics while lands covered with evergreen needle-leaved trees are estimated with the highest [Formula: see text] decline in noncroplands. We identify soil nitrogen, land cover, and precipitation Seasonality Index as the most significant parameters in explaining the SOC's variability. The findings provide insights into SOC dynamics under increased soil salinity, improving understanding of SOC stock responses to land degradation and climate warming.

Improving soil organic carbon mapping in farmlands using machine learning models and complex cropping system information

Obtaining accurate spatial maps of soil organic carbon (SOC) in farmlands is crucial for assessing soil quality and achieving precision agriculture. The cropping system is an important factor that affects the soil carbon cycle in farmlands, and different agricultural managements under different cropping systems lead to spatial heterogeneity of SOC. However, current research often ignores differences in the main controlling factors of SOC under different cropping systems, especially when the cropping pattern is complex, which is not conducive to farmland zoning management. This study aims to (i) obtain the spatial distribution map of six cropping systems by using multi-phase HJ-CCD satellite images; (ii) explore the stratified heterogeneous relationship between SOC and environmental variables under different cropping systems by using the Cubist model; and (iii) predict the spatial map of SOC. The Xiantao, Tianmen, and Qianjiang cities, which are the core agricultural areas of the Jianghan Plain, were selected as the study area. Results showed that the SOC content in rice–wheat rotation was the highest among the six cropping systems. The Cubist model outperformed random forest, ordinary kriging, and multiple linear regression in SOC mapping. The results of the Cubist model showed that cropping system, climate, soil attributes, and vegetation index were important influencing factors of SOC in farmlands. The main controlling factors of SOC under different cropping systems were different. Specifically, summer crop types had a greater influence on spatial variations in SOC than winter crops. Paddy–upland rotation was more affected by river distance and NDVI, while upland–upland rotation was more affected by irrigation-related factors. This work highlights the differentiated main controlling factors of SOC under different cropping systems and provides data support for farmland zoning management. The Cubist model can improve the prediction accuracy of SOC under complex cropping systems.

Spatial variation of soil organic carbon under major rubber planting regions in China

AbstractUnderstanding the dynamic relationships between soil organic carbon (SOC) and stand age are essential to quantify and predict the terrestrial carbon sequestration potential. However, the spatial patterns in the response of rubber plantation SOC to stand age and their driving factors remain unclear. Based on SOC and its components measurement at different soil depths (0–40 cm) in rubber plantations under five different age classes (0–5, 5–10, 10–20, 20–30, and &gt;30 years) in three major rubber cultivation regions in China, distribution pattern and controlling factors of SOC were investigated. We found that SOC and its components showed significant spatial variability vertically with soil depth and laterally across sampling sites. SOC contents in three major rubber cultivation regions range from 4.48 to 20.13 g kg−1 at a depth of 0–40 cm. Among the sampling sites, Jinghong had the highest SOC content at a depth of 0–10 cm (20.13 g kg−1). On a large‐scale, the relationship between SOC and stand age in rubber plantations did not show a consistent pattern among different sampling sites. Additionally, annual rainfall, soil moisture content, and soil pH had a stronger impact on SOC in rubber plantations compared to stand age. The results indicated that the spatial variability of SOC in rubber plantations with stand age could be influenced by specific soil properties and climate‐related variables at each sampling site. This study emphasized the significance of conducting multi‐site, multi‐scale studies to enhance our understanding of SOC dynamics and its influencing factors, and help to more accurately predict the dynamic changes of soil carbon storage in rubber plantations.

Temporal and depth‐dependent variations in soil aggregate‐associated organic carbon in reclaimed coastal poplar plantations

AbstractCoastal reclamation alters the ecological environment of wetlands and influences global carbon cycles. However, variations in soil organic carbon fractions and stability in the soil profile during reclamation, particularly in the subsoil, remain unclear. In this study, soil aggregate‐associated organic carbon and its stability were investigated in soil profiles (0–100 cm) at different reclamation times (0, 24, 44, and 64 years) in coastal poplar plantations in East China. Total soil organic carbon concentrations in the topsoil (0–40 cm) increased with increasing reclamation time but varied little in the subsoil (40–100 cm). In the topsoil, the soil organic carbon concentrations in different aggregate fractions tended to increase with increasing reclamation time, which was enhanced mainly by particulate organic carbon within macro‐aggregates. In the subsoil, soil organic carbon concentrations increased in the micro‐aggregate fraction and decreased in the silt and clay fraction with increasing reclamation time, whereas the opposite changes led to smaller variations in total soil organic carbon. This relative balance was regulated by micro‐aggregate formation via new organic matter input (e.g., root litter) and old mineral‐associated organic carbon depletion. Regardless of the soil horizon, soil aggregate stability increased with reclamation time, whereas the total particulate organic carbon/mineral‐associated organic carbon ratio increased with increasing reclamation time, implying that the soil organic carbon stability decreased, which may be attributed to an increase in the vulnerability of soil organic matter to mineralization as the reclamation progresses. These findings indicate that long‐term plantation development influences aggregate‐associated organic carbon accrual throughout the soil profile in reclaimed coastal land. Thus, effective management is required to improve soil organic carbon accrual in coastal woodland subsoil, which is crucial for increasing soil carbon sequestration.

Is the organic carbon-to-clay ratio a reliable indicator of soil health?

Climate action plans under the Paris Climate Agreement and other national commitments aimed at improving soil-based ecosystem services require the operational monitoring of soil carbon (C). The European Union is aiming to enhance soil health, and as part of the proposed Soil Monitoring Law, the European Commission recommends the monitoring of the soil C loss indicator among other soil health indicators. In this study, we evaluate the feasibility of the proposed soil C loss indicator by assessing its performance using the EU-wide 2009 LUCAS soil survey data. The proposed indicator is the soil organic carbon (SOC) to clay ratio, with a threshold value of 1:13. The results are also compared with the C stock changes reported by countries to the climate convention (UNFCCC). Our results reveal that the variation in SOC and clay content at European scale exceeds that of the data used to develop the proposed indicator. We also found that the variation in the SOC content was influenced not only by clay content but also by climate and land-use reflecting C input levels. Therefore, the defined threshold is inadequate for detecting degraded soils if the SOC and clay content are beyond the conditions used to establish the criteria. Furthermore, major discrepancies were observed between the soil carbon stock changes reported by the national greenhouse gas (GHG) inventories and the proportions of degraded soils identified by using the soil C loss indicator. We conclude that employing a single indicator such as SOC:Clay ratio with one threshold value for all soils across various land covers, management practices, and climatic conditions, as defined by the European Commission for the Soil Monitoring Law, is inappropriate for monitoring soil C loss.

Coastal reclamation alters soil organic carbon dynamics: A meta-analysis in China

As an important blue carbon pool, the content, dynamics, and related hydrological environment of coastal soil organic carbon (SOC) are extremely vulnerable to coastal reclamation; however, a full understanding of this is still lacking, mainly due to the heterogeneity in space. In this study, a dataset encompassing 680 samples gathered from 128 literatures related to SOC variation in China’s coastal areas has been constructed. Moreover, meta-analysis combined with structural equation model have been adopted to quantitatively explore the characteristics and causal mechanism of SOC change following reclamation. The results show that: (1) After reclamation, reclamation history has become an overriding control variable dominating all environmental factors, including soil physical and biochemical factors, and directly alters the content and dynamics of SOC. The SOC has tended to decrease substantially within first 10 years after reclamation and then increase significantly over time. After reclamation, forest and paddy generally have a positive effect on SOC. (2) In natural saltmarshes (before reclamation), soil biochemical factors are the dominant forces driving SOC. However, after reclamation, soil physical factors have played an increasingly important role in SOC variation, of which soil moisture is a relatively important contributor. Total nitrogen is another driving force controlling the variation of SOC acting as a gate valve role. (3) For coastal carbon sequestration, cultivating terricolous salt-tolerant vegetation to establish integrated high salinity eco-system in reclaimed zones, wetland silting promotion projects should be encouraged in natural salt marshes. And, land uses of forest and paddy should be popularized for promoting SOC in reclaimed zones.

Effects of Organic Matter Addition on Soil Carbon Contents, CO2 Emissions, and Bacterial Compositions in a Paddy Field in South China

Increasing soil organic carbon (SOC) contents and reducing carbon dioxide (CO2) emissions in paddy soil fields can result in positive impacts on climate change mitigation and soil quality. However, SOC accumulation and its microbial driving factors under enhanced fertilization strategies (e.g., organic matter application) are still unclear. Therefore, we investigated the effects of organic matter addition on SOC variations, CO2 fluxes, and their relationships with soil bacterial compositions and functions through a 6-year fertilizer experiment in rice fields involving two fertilization types, namely chemical fertilizer (NPK) and chemical fertilizer combined with organic matter (NPK+OM). The results showed significantly higher and lower SOC contents (p &lt; 0.05) in the 10–20 cm soil layer under the NPK+OM treatment before rice transplanting and after rice harvest, respectively, than those under the NPK treatment. The lower SOC contents after rice harvest might be due to the great nutrient consumption, resulting in higher rice yields in the NPK+OM than those in the NPK treatment by 6.68 to 32.35%. Compared with NPK, NPK+OM reduced the in-situ CO2 fluxes by 38.70–118.59%. However, the ex-situ SOC mineralization rates were not affected by NPK+OM in the 0–10 and 10–20 cm soil layers. The 16S rRNA sequence indicated a significant increase in the abundance of non-singleton amplicon sequence variants (ASVs) in the NPK+OM treatment scenario compared to those in the NPK treatment scenario. The top three most important soil bacterial phylum influenced by NPK+OM were LCP-89, BRC1, and Rokubacteria in April, as well as Firmicutes, Nitrospinae, and BRC1 in July. Soil Actinobacteria was negatively correlated with the SOC contents in April and July. The results of the present study demonstrate the economic and ecological benefits of the organic matter addition in rice production, as well as the contribution of soil bacteria to SOC accumulation and CO2 emission reduction.

Spatiotemporal Evolution and Prediction of Land Use and Carbon Stock in Shanghai

Soil organic carbon (SOC) constitutes a critical component of carbon reservoirs within terrestrial ecosystems. The ramifications of urban land use transitions on SOC dynamics, particularly in rapidly urbanizing regions such as Shanghai, remain insufficiently elucidated. This investigation synergizes a predictive land use change model (Logistic-CA-Markov) with an ecosystem service quantification framework (InVEST), aiming to delineate the interplay between SOC variability and Land Use and Land Cover Change (LUCC) under natural development and ecological protection scenarios. Empirical observations from 2010 to 2020 reveal a contraction in Shanghai’s agricultural land of 34,912.76 hectares, juxtaposed with an expansion of urban built-up areas of 36,048.24 hectares. Projections for 2030 under an ecological protection scenario indicate a moderated urban sprawl, reducing built-up area expansion by 13,518 hectares relative to the natural development scenario. Notably, the net carbon sequestration capacity of Shanghai is anticipated to diminish by approximately 0.418 million tons between 2020 and 2030. This trend is observed under both considered scenarios, forecasting a cumulative reduction in SOC stocks exceeding 1 million tons by 2030. The natural development pathway portends a more pronounced and accelerated depletion of SOC reserves. Although ecological conservation measures show the potential to decelerate this loss, they appear insufficient to reverse the ongoing decline in SOC stocks. This study advocates for strategic urban planning interventions focused on constraining the growth of building densities and augmenting the preservation and management of eco-lands. Such measures are imperative for bolstering Shanghai’s carbon sequestration capacity.

Effects of fresh-salt water interaction on spatial variations of soil organic carbon in reed wetland of Yellow River Estuary.

Estuarine wetlands exhibit significant interaction between fresh and salt water, with long-term carbon sequestration capability. We set up 60 sampling sites in the reed wetlands of the fresh-salt water interaction zone of the Yellow River Estuary, covering four different zones of the weak-intensity fresh-salt water interaction zone (WIZ), medium-intensity fresh-salt water interaction zone (MIZ), high-intensity interaction fresh-salt water zone (HIZ) and strong-intensity fresh-salt water interaction zone (SIZ). We investigated how fresh-salt water interaction affected the spatial variation of soil organic carbon (SOC) storage. The results showed that the area of reed wetland accounted for 17.8% of the total area of the fresh-salt water interaction zone the Yellow River Estuary, which mainly distributed in the WIZ and MIZ. The SOC content of reed wetland in the fresh-salt water interaction zone ranged from 1.09 to 3.65 g·kg-1, the SOC density was between 1.85-5.84 kg·m-2, and the SOC storage was (17.32±3.64)×104 t. The SOC content and SOC density decreased with increasing fresh-salt water interaction. There were significant differences in surface SOC content between different subzones of the fresh-salt water interaction zone. The surface SOC content decreased significantly with the increases of fresh-salt water interaction intensity. SOC density was positively correlated with SOC, TN, NH4+-N, and biomass, but negatively correlated with salt ions, soil bulk density, pH, and EC. SOC storage in the 0-30 cm soil layer accounted for 50.9%-64.2% of that in the 0-60 cm soil layer, while SOC storage in the 0-60 cm soil layer occupied 19.1%-37.7% of that in the 0-400 cm soil layer. The results could provide a scientific basis for accurately evaluating SOC storage of estuarine wetlands, improving carbon sink function and wetland management.

Predicting organic carbon in European soils: Only in Southern Ukraine can we expect an increase in humus content

Soil organic carbon comprises the majority of the terrestrial soil carbon pool and plays an important role in the global carbon cycle and balance. Even minor changes in soil organic carbon (SOC) can have a significant impact, not only on climate but also on ecosystem stability, due to its key role in soil-atmosphere carbon exchange, plant growth, and food production. In order to assess the feedbacks between the terrestrial carbon cycle and climate change, and to maintain ecosystem functions, it is crucial to understand the spatial and temporal changes in SOC and the drivers of these changes. The role of soil as a source or sink of atmospheric CO2 is primarily influenced by changes in climate and soil water content. Climate change, particularly global warming, can have a direct or indirect impact on the decomposition of organic matter by regulating soil microbes and fauna, enzyme activity, and soil respiration. A warming climate may increase the loss of soil carbon to the atmosphere because warming has a stronger effect on respiration than on photosynthesis, resulting in a positive soil carbon-climate feedback. Climate warming can significantly affect soil organic matter stocks, with the magnitude of the effect largely dependent on the initial organic matter stock size. Soil carbon content is a crucial aspect of terrestrial ecosystems that affects their functional properties and the climate. Conversely, climate also has an impact on soil organic carbon content. The spatial variability of soil organic carbon content and the predictions made for the west-central European region are also important considerations. The study identified the spatial variation of soil organic carbon throughout Europe and forecast its dynamics in the next 50–70 years, considering global climate change. Digital soil mapping enables a more precise representation of soil properties in space, including the spatial quantification of prediction errors. The accuracy of these predictions increases as more local observations, such as soil profiles, are available to construct the prediction model. Digital soil mapping allows flexible spatial development of soil property maps. Soil properties, such as nutrient concentration and stocks, carbon, heavy metals, pH, cation exchange capacity, and physical properties like particle size and bulk density, can be modelled at different depths and spatial resolutions depending on the project's objectives and available input data. The r GSOCmap project used a 1 km grid to model soil organic matter content. In Europe, the range of soil organic carbon content is from 0 to 750 t/ha, with a mean of 78.1 t/ha and a standard deviation of 50.1 t/ha. Climatic factors were found to account for 29% of the variation in soil organic carbon based on regression analysis. The study revealed that an increase in air temperature leads to a decrease in soil organic carbon content, while an increase in precipitation results in an increase in this indicator. Additionally, the content of soil organic matter is negatively impacted by an increase in the seasonality of precipitation. According to the forecast, global climate change will cause an increase of 1.0–1.1 t/ha in the organic carbon content of 3.6% of the continent's area over the next 70 years. On 7.6% of the area, the changes will be insignificant. The soil organic carbon content is expected to decrease on 88.9% of the area. Of this, 35.1% will experience a slight decrease in carbon content by 0–1 t/ha, 28.4% will experience a moderate decrease in soil organic carbon content by 1.0–1.1 t/ha, and 25.3% will experience a significant decrease by 1.1–1.3 t/ha. The Baltic countries, Belarus, and the Black Earth zone of Russia are at the highest risk. The risk of Russia becoming highly dependent on food imports is increased by this fact. The prospects for Ukraine are quite optimistic. Even in the northern Azov region, we can expect an intensification of humus accumulation processes in the near future, mainly due to increased precipitation. Precipitation in southern Ukraine is a limiting factor that significantly affects agricultural productivity. Increased precipitation and organic matter growth in the soil present positive prospects for agriculture in southern Ukraine, including the northern Azov, Black Sea, and Crimea. It is possible that the occupation of these territories, which are promising for agricultural production, is one of the goals of Russian armed aggression against Ukraine.

A high-resolution map of soil organic carbon in cropland of Southern China

An accurate and fine map of soil organic carbon (SOC) plays a vital role in understanding the global carbon cycle and achieving soil carbon sequestration potential. Although global and national maps of SOC are already available with various spatial resolutions, limited sample size, and relative coarse resolution hinder its accuracy and application in local regions. Here, we collected 13,424 soil samples and information of 45 environmental covariates from cropland in Jiangxi Province, Southern China during 2012 and 2013. Then, the optimal covariates were selected by a recursive feature elimination algorithm for mapping SOC. After that, we deployed the random forest (RF) to produce a fine map (30 m) of SOC in the cropland of Jiangxi Province and 100 times bootstrapping was performed to calculate the prediction uncertainty. Finally, we determined the impacts of various covariates on SOC variability using RF and partial least squares structural equation modeling. Our results showed that compared with the predictive model without soil management information, introducing soil management information improved the predictability of SOC with an increase in R2 by 7.35 % (0.73 vs 0.68) and decrease in RMSE by 7.03 % (2.91 vs 3.13 g kg−1). Our results well estimated the uncertainty of the predicted result with a PICP of 0.91 for a 90 % prediction interval. Soil properties and soil management activities make the largest contribution for modelling SOC. Specifically, the total nitrogen content, straw return amount, total potassium content, and multi-resolution valley bottom flatness were found as the most important factors for mapping SOC in the cropland of our study area. Overall, this study deepened our knowledge of the variation of SOC and also emphasizes that incorporating soil management information could help us to achieve more accurate predictions of SOC.

Selective uneven enrichment of soil organic carbon among different-sized sediments under a rain-induced overland flow: 13C stable isotope evidence

Soil organic carbon (SOC) enrichment varies among sediments of different sizes during rain-induced overland flow erosion. This selective transport of SOC is complex in conjunction with the exposure of labile and stable organic carbon (OC), accompanied by heterogeneous aggregate disintegration under raindrop effects. Utilizing the variations in δ13C values of SOC fractions, we traced this selective transport, linking it to aggregate-wrapped SOC changes during erosion. A modified soil pan facilitated the simultaneous monitoring of splash and sheet erosion via artificially simulated rainfall, with control over the intensity and slope. Aggregate composition, SOC distribution, and δ13C values in the erosion samples were analyzed. The results indicated that distinct sorting existed within the aggregate fragments. Along with SOC variation among different sediment sizes, the proportions of clay and fine silt within sediment aggregates increased as a function of slope and rainfall intensity, whereas particulate OC within aggregates decreased. The SOC enrichment ratios (ERocs) and δ13C values in splash-eroded sediments were positively correlated with those in sheet-eroded sediments. The ERocs in splash-eroded sediments were lower than those in sheet-eroded sediments, but δ13C values were the opposite. Moreover, δ13C values of SOC enriched in sediment particles of all sizes from aggregate stripping were lower than those of the original soil. This indicates that raindrop hits promote heavy C loss during sheet erosion, which is different for mineral-associated and particulate OC. As the slope and rainfall intensity increased, δ13C values for all sediment sizes decreased over the course of erosion. Interestingly, the highest δ13C values were observed under a rainfall intensity of 60 mm h−1, whereas the highest SOC concentrations were noted on a 5° slope. These observations suggest divergent mechanisms affect δ13C values and SOC concentrations in eroded sediments. All these results verified that selective sorting existed for the light SOC fraction. Finally, the internal selective transport of one SOC fraction may explain the enhanced mineralization and reaggregation capacity of the deposited sediments.

Spatial Variability and Statistical Analysis of Soil Properties in the Rice Wheat-Based Systems of North-West India

ABSTRACT There are limited reports about the impacts of long-term rice wheat cropping system (RWCS) on soil properties and nutrient stocks under smallholder farmer’s conditions in developing counties. The study was carried out in RWCS in Haryana (10 districts) of North-West India in order to map out some soil properties and assess their variability within the area. From the study area, a total of 150 surface soil samples (15 samples each district) were collected using Global Positioning System (GPS) after harvest of wheat crop. Then, soil properties, that is, pH, electrical conductivity (EC), soil organic carbon (SOC), carbonate content, cation exchange capacity (CEC), salinity content (Na+, K+, Ca2+ + Mg2+) soil available nutrients (NPK, Fe & Zn), and micronutrient fractions were measured in the laboratory. All soil properties significantly changed under RWCS, except for bulk density, SOC, and SAR variables. The SOC stock varied significantly among the majority of RWCS in north-western India but was not significantly different in total nitrogen (TN) stocks. After log-transformation of data, classical statistics were used to describe the soil properties, and one-way analysis of variance. The PCA chosen soil properties explained 81.37% of the soil quality variability among the RWCS. Such soil properties and nutrient stock variability among the RWCS suggested the introduction of suitable management practices that sustain the soil system of the RWCS with poor properties and nutrients. On the basis of the linear function, soil chemical properties (44.65%) contributed more to soil quality index (SQI) than physical ones.

Recovery of soil organic carbon storage driven by microbial communities during long-term natural restoration in wetland ecosystems

Natural restoration offers a positive strategy for maintaining biodiversity and addressing climate change. Wetland is an important “carbon sink”, yet the dynamic of soil organic carbon (SOC) storage and how it is driven by microbial communities and activities remain unclear during natural restoration. In this work, we investigated the variations of soil organic carbon (SOC) storage, bacterial and fungal communities, as well as microbial activities (including microbial biomass carbon, carbon mineralization rate and extracellular enzymes) in naturally restored wetlands with restoration years of 0 (rice field reclaimed from natural wetland), 15, 20 and 40 in the Poyang Lake wetland. Results showed that SOC storage had been restored to its natural level after 20 years of natural rejuvenation, which was driven by microbial communities via impacting oxidase (peroxidase), microbial biomass and microbial quotient. Fungal diversity and community composition had strong positive effects on SOC storage, while the role of bacteria was limited, emphasizing that fungi exerted a more important control over carbon stock during natural restoration. Fungal taxa Sordariomycetes and Eurotiomycetes were the dominant microbial predictors of SOC storage. Besides, natural restoration significantly shifted bacteria and fungi communities, as well as microbial activities toward a pattern similar to that of natural wetlands. To sum up, our results highlight the significance of natural restoration for recovering carbon storage, and the addition of microbial attributes can potentially improve our capacity to predict changes in SOC storage in wetland ecosystems.